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Filed Pursuant to Rule 424(b)(5)
Registration No. 333-223575

11,111,111 Shares

Ordinary Shares

We are offering 11,111,111 of our ordinary shares.

Our ordinary shares are listed on The Nasdaq Global Select Market under the symbol "SBBP." On September 15, 2020, the last reported sale price of our ordinary shares on The Nasdaq Global Select Market was $2.83 per share.

Investing in our ordinary shares involves a high degree of risk. See "Risk Factors" on page S-6 of this prospectus supplement and in the documents incorporated by reference into this prospectus supplement.

We are an "emerging growth company" as defined in the Jumpstart Our Business Startups Act of 2012, as amended, and, as such, we are subject to reduced public company reporting requirements. See "Prospectus Supplement Summary — Implications of Being an Emerging Growth Company and a Smaller Reporting Company."

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

For the avoidance of doubt, this document is not intended to be and is not a prospectus for the purposes of the Companies Act 2014 of Ireland, Regulation (EU) 2017/1129 of 14 June 2017 (as amended), the European Union (Prospectus) Regulations 2019, or the Central Bank (Investment Market Conduct) Rules (S.I. No. 366 of 2019); and the Central Bank of Ireland has not approved this document.

(1)

See "Underwriting" beginning on page S-51 for a description of compensation payable to the underwriters.

Delivery of the ordinary shares is expected to be made on or about September 21, 2020. We have granted the underwriters an option for a period of 30 days to purchase an additional 1,666,666 of our ordinary shares. If the underwriters exercise the option in full, the total underwriting discounts and commissions payable by us will be $1,725,000.

Joint Book-Running Managers

Lead Managers

Prospectus Supplement dated September 16, 2020

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ABOUT THIS PROSPECTUS SUPPLEMENT

This prospectus supplement and the accompanying prospectus are part of a "shelf" registration statement on Form S-3 that we initially filed with the U.S. Securities and Exchange Commission, or the SEC, on March 12, 2018, and that was declared effective by the SEC on March 27, 2018. This prospectus supplement and the accompanying prospectus relate to the offering of our ordinary shares. Before buying any of the ordinary shares that we are offering, we urge you to carefully read this prospectus supplement, the accompanying prospectus, any free writing prospectus that we have authorized for use in connection with this offering, and the information incorporated by reference as described under the headings "Where You Can Find More Information" and "Incorporation of Information by Reference" in this prospectus supplement. These documents contain important information that you should consider when making your investment decision.

This document is comprised of two parts. The first part is this prospectus supplement, which describes the specific terms of this offering and also adds to, and updates information contained in, the accompanying prospectus and the documents incorporated by reference into this prospectus supplement and the accompanying prospectus. The second part, the accompanying prospectus, including the documents incorporated by reference into the accompanying prospectus, provides more general information, some of which may not apply to this offering. Generally, when we refer to this prospectus, we are referring to the combined document consisting of this prospectus supplement and the accompanying prospectus. In this prospectus supplement, as permitted by law, we "incorporate by reference" information from other documents that we file with the SEC. This means that we can disclose important information to you by referring to those documents. The information incorporated by reference is considered to be a part of this prospectus supplement and the accompanying prospectus and should be read with the same care. When we make future filings with the SEC to update the information contained in documents that have been incorporated by reference, the information included or incorporated by reference in this prospectus supplement is considered to be automatically updated and superseded. In other words, in case of a conflict or inconsistency between information contained in this prospectus supplement and information in the accompanying prospectus or incorporated by reference into this prospectus supplement, you should rely on the information contained in the document that was filed later.

You should rely only on the information contained in, or incorporated by reference into, this prospectus supplement, the accompanying prospectus, and in any free writing prospectus that we have authorized for use in connection with this offering. We have not, and the underwriters have not, authorized any other person to provide you with different information. We are not, and the underwriters are not, making an offer to sell or soliciting an offer to buy our securities in any jurisdiction in which an offer or solicitation is not authorized or in which the person making that offer or solicitation is not qualified to do so or to anyone to whom it is unlawful to make an offer or solicitation. You should assume that the information appearing in this prospectus supplement, the accompanying prospectus, the documents incorporated by reference into this prospectus supplement and the accompanying prospectus, and in any free writing prospectus that we have authorized for use in connection with this offering, is accurate only as of the date of those respective documents. Our business, financial condition, results of operations, and prospects may have changed since those dates.

References in this prospectus supplement and the accompanying prospectus to the terms "we," "us," "our" or "Strongbridge" or other similar terms mean Strongbridge Biopharma plc and its consolidated subsidiaries, unless we state otherwise or the context indicates otherwise.

This prospectus supplement, the accompanying prospectus and the information incorporated by reference herein and therein includes our trademarks, trade names and service marks, such as "Strongbridge Biopharma" and "RECORLEV." This prospectus supplement, the accompanying prospectus and the information incorporated by reference herein and therein also contains references to trademarks belonging

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to other entities. Solely for convenience, trademarks and trade names referred to in this prospectus supplement, the accompanying prospectus and the information incorporated by reference herein and therein, including logos, artwork and other visual displays, may appear without the ^{<I 07>®</I 07 1>} or ^TM symbols, but such references are not intended to indicate, in any way, that we will not assert, to the fullest extent under applicable law, the rights of the applicable licensor to these trademarks and trade names. We do not intend our use or display of other companies' trade names or trademarks to imply a relationship with, or endorsement or sponsorship of us by, any other company.

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CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

Some of the statements in this prospectus supplement, the accompanying prospectus and incorporated herein and therein by reference constitute "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21E of the Exchange Act. These statements relate to future events concerning our business and to our future revenues, operating results and financial condition. In some cases, you can identify forward-looking statements by terminology such as "may," "will," "could," "would," "should," "expect," "plan," "anticipate," "intend," "believe," "estimate," "forecast," "predict," "propose," "potential" or "continue," or the negative of those terms or other comparable terminology. Forward-looking statements may include statements regarding:

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our ability to effectively manage our business through the ongoing COVID-19 pandemic;



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our ability to successfully commercialize Keveyis (dichlorphenamide);



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our ability to obtain and maintain regulatory approval for RECORLEV (levoketoconazole) or any other product candidate;



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our ability to successfully commercialize RECORLEV, if approved, and any other product candidate we receive approval for;



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the timing, progress and results of clinical and preclinical trials for our product candidates;



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our future borrowing capacity under our existing credit facility and our ability to secure additional financing when needed on acceptable terms;



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our ability to effectively manage our anticipated growth;



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our ability to develop our commercial organization and recruit and retain qualified sales representatives;



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our ability to successfully implement our business model, as well as strategic plans for our business, product candidates and technology;



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our ability to implement and execute our business strategy to in-license, acquire and develop new product candidates;



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our ability to retain our key personnel and our ability to recruit, retain and motivate additional qualified personnel;



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our ability to develop and maintain relationships with manufacturers, clinical research organizations and other important contractors and consultants;



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our ability to expand, protect and enforce our intellectual property rights;



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our ability to obtain and maintain orphan drug exclusivity for Keveyis or our product candidates;



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the impact of government laws and regulations in the United States and foreign countries; and



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our expected use of proceeds from this offering.

Any forward looking statements contained in this prospectus supplement, the accompanying prospectus or incorporated herein or therein by reference are only estimates or predictions of future events based on information currently available to our management and management's current beliefs about the potential outcome of future events. Whether these future events will occur as management anticipates, whether we will achieve our business objectives, and whether our revenues, operating results or financial condition will improve in future periods are subject to numerous risks. There are a number of important factors that could cause actual results to differ materially from the results anticipated by these forward-looking statements. These important factors include those that we discuss under the heading "Risk Factors" and in other sections of our Annual Report on Form 10-K for the year ended December 31, 2019, or the 2019 Annual Report, our Quarterly Report on Form 10-Q for the fiscal quarter ended June 30, 2020, or the Q2 2020 Quarterly Report, as well as in subsequent reports we file from time to time with the SEC, that are incorporated by reference into this prospectus supplement and the accompanying prospectus. You should read these factors and the other cautionary statements made in this prospectus supplement, the

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accompanying prospectus and in the documents we incorporate by reference herein and therein as being applicable to all related forward-looking statements wherever they appear in this prospectus supplement, the accompanying prospectus or the documents we incorporate by reference into this prospectus supplement and the accompanying prospectus. If one or more of these factors materialize, or if any underlying assumptions prove incorrect, our actual results, performance or achievements may vary materially from any future results, performance or achievements expressed or implied by these forward-looking statements. We undertake no obligation to publicly update any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law.

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RISK FACTORS

Investing in our ordinary shares involves a high degree of risk. Our business, prospects, financial condition or operating results could be materially adversely affected by the risks identified below, as well as other risks not currently known to us or that we currently consider immaterial. The trading price of our ordinary shares could decline due to any of these risks, and you may lose all or part of your investment. In assessing the risks described below, you should also refer to the information contained in the 2019 Annual Report, in the Q2 2020 Quarterly Report,and in the other documents which are incorporated by reference in this prospectus supplement and the accompanying prospectus in their entirety.

Risks Related to the Offering

Management will have broad discretion as to the use of the net proceeds from this offering, and we may not use the proceeds effectively.

Our management will have broad discretion as to the application of the net proceeds and could use them for purposes other than those contemplated at the time of this offering. Our shareholders may not agree with the manner in which our management chooses to allocate and spend the net proceeds. Moreover, our management may use the net proceeds for corporate purposes that may not increase our market value.

Investors in this offering will experience immediate and substantial dilution.

The public offering price of the ordinary shares offered pursuant to this prospectus supplement may be substantially higher than the pro forma net tangible book value per share of our ordinary shares. Therefore, if you purchase ordinary shares in this offering, you will incur immediate and substantial dilution in the pro forma net tangible book value per ordinary share from the price per share that you pay for such ordinary shares. If the holders of outstanding options, warrants or other securities convertible into our ordinary shares exercise those options, warrants or other such securities at prices below the public offering price, you will incur further dilution. See "Dilution" on page S-38 of this prospectus supplement for a more detailed discussion of the dilution you will incur in this offering.

Future sales of substantial amounts of our ordinary shares could adversely affect the market price of our ordinary shares.

Future sales of substantial amounts of our ordinary shares, or securities convertible or exchangeable into ordinary shares, into the public market, including ordinary shares issued upon exercise of options and warrants, or perceptions that those sales could occur, could adversely affect the prevailing market price of our ordinary shares and our ability to raise capital in the future.

We have never paid cash dividends, do not expect to pay dividends in the foreseeable future and our ability to pay dividends, or repurchase or redeem our ordinary shares, is limited by law.

We have not paid any dividends since our inception and do not anticipate paying any dividends on our ordinary shares in the foreseeable future. Even if future operations lead to significant levels of distributable profits, we currently intend that any earnings will be reinvested in our business and that dividends will not be paid until we have an established revenue stream to support continuing dividends. The proposal to pay future dividends to shareholders will in addition effectively be at the sole discretion of our board of directors after taking into account various factors our board of directors deems relevant, including our business prospects, capital requirements, financial performance and new product development. In addition, payment of future dividends is subject to certain limitations under the Irish Companies Act 2014 or the Irish Companies Act. The Irish Companies Act, among other requirements, requires Irish companies to have profits available for distribution equal to or greater than the amount of the proposed dividend. In addition, the terms of our existing debt agreement restrict our ability to pay dividends on our ordinary shares. Accordingly, investors cannot rely on dividend income from our ordinary shares and any returns on an investment in our ordinary shares will likely depend entirely upon any future appreciation in the price of our ordinary shares.

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USE OF PROCEEDS

We estimate that the net proceeds from the sale of ordinary shares by us in this offering will be approximately $23.1 million (or approximately $26.6 million if the underwriters exercise their option to purchase additional ordinary shares in full), after deducting the underwriting discounts and commissions and estimated offering expenses payable by us.

We intend to use the net proceeds from this offering to (i) continue development and regulatory activities, to facilitate commercial readiness, and to commercially launch RECORLEV primarily in the United States, (ii) support the life cycle management activities of Keveyis, and (iii) support other general corporate purposes, which may include working capital, capital expenditures, acquisition of additional technologies or other forms of intellectual property, acquisition of assets or businesses that are complementary to our existing business, and general and administrative expenses.

These expected uses of the net proceeds from this offering represent our intentions based upon our current financial condition, results of operations, business plans and conditions. As of the date of this prospectus, we cannot predict with certainty all of the particular uses for the net proceeds to be received upon the closing of this offering or the amounts that we will actually spend on the uses set forth above. The amounts and timing of our actual expenditures may vary significantly depending on numerous factors. As a result, our management will retain broad discretion over the allocation of the net proceeds from this offering.

Pending our use of the net proceeds from this offering as described above, we intend to invest the net proceeds in a variety of capital preservation investments, including short-term, investment-grade, interest-bearing instruments and U.S. government securities.

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DESCRIPTION OF SHARE CAPITAL

General

The following description of our share capital is qualified in its entirety by reference to, and is subject to, the detailed provisions of our memorandum and articles of association, which are incorporated herein by reference as an exhibit to the registration statement of which this prospectus supplement forms a part, and the relevant provisions of Irish law referred to therein, including in particular the Companies Act 2014 of Ireland (as amended), or Irish Companies Act.

Our authorized share capital consists of €40,000, divided into 40,000 deferred ordinary shares with a nominal value of €1.00 per share, and $7,000,000, divided into 600,000,000 ordinary shares with a nominal value of $0.01 per share and 100,000,000 preferred shares with a nominal value of $0.01 per share.

We may issue shares subject to the maximum authorized share capital contained in our Memorandum of Association. The authorized share capital may be increased or reduced by a resolution approved by a simple majority of the votes cast at a general meeting of our shareholders, referred to under Irish law as an "ordinary resolution." Our authorized share capital may be divided into shares of such nominal value as the resolution shall prescribe. As a matter of Irish law, the directors of a company may issue new ordinary or preferred shares without shareholder approval once authorized to do so by the memorandum and articles of association or by an ordinary resolution adopted by our shareholders at a general meeting. The authorization may be granted for a maximum period of five years, at which point it must be renewed by shareholders by an ordinary resolution. Accordingly, our Articles of Association, or Articles, authorize our board of directors to issue new ordinary or preferred shares without shareholder approval for a period of five years ending on August 7, 2020 and this authority was renewed by ordinary resolution at our 2020 annual general meeting held on May 14, 2020 for a period of five years from that date. The authority to issue preferred shares provides us with the flexibility to consider and respond to future business needs and opportunities as they arise from time to time, including in connection with capital raising, financing and acquisition transactions or opportunities.

We may, by ordinary resolution, reduce our authorized share capital in any way. We also may, by special resolution and subject to confirmation by the Irish High Court, reduce or cancel our issued share capital in any manner permitted by the Irish Companies Act.

As of June 30, 2020, we had 40,000 deferred ordinary shares outstanding, 54,355,957 ordinary shares outstanding and zero preferred shares outstanding. As of June 30, 2020, we also had outstanding options to acquire 10,499,222 ordinary shares, warrants to purchase an aggregate of 7,100,643 ordinary shares, and 1,090,300 ordinary shares issuable upon the vesting of restricted stock units.

The following description of our share capital and certain provisions of our Articles are summaries and are qualified by reference to our Articles.

Deferred Shares

The authorized and issued share capital includes 40,000 deferred ordinary shares, which are required in order to satisfy statutory minimum capital requirements of an Irish public limited company. The holders of the deferred ordinary shares are not entitled to receive any dividend or distribution, to attend, speak or vote at any general meeting, and have no effective rights to participate in the assets of our Company. The holders of our deferred ordinary shares are not entitled to a vote.

Ordinary Shares

Under our Articles, each holder of our ordinary shares is entitled to one vote for each ordinary share that he or she holds. Our ordinary shares do not have sinking fund provisions.

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Preferred Shares

Our board of directors is authorized to issue preferred shares on a non-pre-emptive basis, with discretion as to the terms attaching to the preferred shares, including as to voting, dividend and conversion rights and priority relative to other classes of shares with respect to dividends and upon a liquidation. This authority will expire on May 14, 2025.

Notwithstanding this authority, under the Irish Takeover Rules our board of directors would not be permitted to issue any of our shares, including preferred shares, during a period when an offer has been made for us or is believed to be imminent unless the issue is (i) approved by our shareholders at a general meeting; (ii) consented to by the Irish Takeover Panel on the basis it would not constitute action frustrating the offer; (iii) consented to by the Irish Takeover Panel and approved by the holders of more than 50% of our shares carrying voting rights; (iv) consented to by the Irish Takeover Panel in circumstances where a contract for the issue of the shares had been entered into prior to that period; or (v) consented to by the Irish Takeover Panel in circumstances where the issue of the shares was decided by our directors prior to that period and either action has been taken to implement the issuance (whether in part or in full) prior to such period or the issuance was otherwise in the ordinary course of business.

While we do not have any current specific plans, arrangements or understandings, written or oral, to issue any preferred shares for any purpose, we are continually evaluating our financial position and analyzing the possible benefits of issuing additional debt securities, equity securities, convertible securities or a combination thereof in connection with, among other things: (i) repaying indebtedness; (ii) financing acquisitions; or (iii) strengthening our balance sheet. The availability of preferred shares gives us flexibility to respond to future capital raising, financing and acquisition needs and opportunities without the delay and expense associated with holding an extraordinary general meeting of our shareholders to obtain further shareholder approval.

Preemption Rights

Under Irish law, unless otherwise authorized, when an Irish public limited company issues shares for cash to new shareholders, it is required first to offer those shares on the same or more favorable terms to existing shareholders of the company on a pro rata basis, commonly referred to as the statutory preemption right. However, we have opted out of these preemption rights in our Articles as permitted under Irish law for a period of five years ending on August 7,2020. Irish law requires this opt-out to be renewed every five years by a special resolution of our shareholders, which requires the approval of not less than 75% of the votes of our shareholders cast at a general meeting. This opt-out was renewed by special resolution at our 2020 annual general meeting held on May 14, 2020 for a period of five years from that date. If the opt-out is not renewed, shares issued for cash after the expiry of the opt-out will have to be offered to pre-existing shareholders of Strongbridge pro rata to their existing shareholding before the shares can be issued to any new shareholders. The statutory preemption rights do not apply where shares are issued for non-cash consideration and do not apply to the issue of non-equity shares (that is, shares that have the right to participate only up to a specified amount in any income or capital distribution).

Dividends

Under Irish law, dividends and distributions may only be made from distributable reserves. Distributable reserves generally means accumulated realized profits less accumulated realized losses and includes reserves created by way of capital reduction. In addition, no distribution or dividend may be made unless our net assets are equal to, or in excess of, the aggregate of our called up share capital plus undistributable reserves and the distribution does not reduce our net assets below such aggregate. Undistributable reserves include undenominated capital and the amount by which our accumulated unrealized profits, so far as not previously utilized by any capitalization, exceed our accumulated unrealized losses, so far as not previously written off in a reduction of capital approved by the Irish High Court without restriction, or a reorganization of capital.

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The determination as to whether or not we have sufficient distributable reserves to fund a dividend must be made by reference to our "relevant financial statements." The "relevant financial statements" will be either the last set of unconsolidated annual audited financial statements or other financial statements properly prepared in accordance with the Irish Companies Act, which give a "true and fair view" of our unconsolidated financial position and accord with accepted accounting practice.

The mechanism as to who declares a dividend and when a dividend shall become payable is governed by our Articles. Our Articles authorize our board of directors to declare dividends without shareholder approval to the extent they appear justified by profits lawfully available for distribution. Our board of directors may also recommend a dividend to be approved and declared by the shareholders at a general meeting. Our board of directors may direct that the payment be made by distribution of assets, shares or cash, and no dividend issued may exceed the amount recommended by our board of directors. Dividends may be declared and paid in the form of cash or non-cash assets and may be paid in dollars or any other currency.

Our board of directors may deduct from any dividend payable to any shareholder any amounts payable by such shareholder to us in relation to our ordinary shares.

Our board of directors may also authorize us to issue shares with preferred rights to participate in dividends we declare. The holders of preferred shares may, depending on their terms, rank senior to the ordinary shares in terms of dividend rights or be entitled to claim arrears of a declared dividend out of subsequently declared dividends in priority to ordinary shareholders.

Bonus Shares

Under our Articles, our board of directors may resolve to capitalize any amount credited to any reserve, including our undenominated capital, or credited to the profit and loss account, and use such amount for the issuance to shareholders of shares as fully paid bonus shares on the same basis of entitlement as would apply in respect of a dividend distribution.

Share Repurchases and Redemptions

Overview

Our Articles provide that any ordinary share that we have agreed to acquire shall be deemed to be a redeemable share. Accordingly, for Irish law purposes, the repurchase of ordinary shares by us may technically be effected as a redemption of those shares as described under "—Repurchases and Redemptions." If our Articles did not contain such provision, repurchases by us would be subject to many of the same rules that apply to purchases of ordinary shares by subsidiaries described under "—Purchases by Subsidiaries," including the shareholder approval requirements described below, and the requirement that any purchases on market be effected on a "recognized stock exchange," which, for purposes of Irish law, includes Nasdaq.

Repurchases and Redemptions

Under Irish law, subject to the conditions summarized below, a company may issue redeemable shares and may only redeem them out of distributable reserves or the proceeds of a new issue of shares for that purpose. We do not expect to have any distributable reserves for the foreseeable future. We may only issue redeemable shares if the nominal value of the issued share capital that is not redeemable is not less than 10% of the nominal value of our total issued share capital. All redeemable shares must also be fully paid and the terms of redemption of the shares must provide for payment on redemption. Redeemable shares may, upon redemption, be cancelled or held in treasury. Based on the provision of our Articles described above, shareholder approval will not be required to redeem our ordinary shares.

We may also be given an additional general authority to purchase our own shares on market, which would take effect on the same terms and be subject to the same conditions as applicable to purchases by our subsidiaries as described below.

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Our board of directors may also issue preferred shares, which may be redeemed at the option of either us or the shareholder, depending on the terms of such preferred shares. Please see "—Authorized Share Capital" above for additional information on preferred shares.

Repurchased and redeemed shares may be cancelled or held as treasury shares. The nominal value of treasury shares held by us at any time must not exceed 10% of the nominal value of our issued share capital. We may not exercise any voting rights in respect of any shares held as treasury shares. Treasury shares may be cancelled by us or re-issued subject to certain conditions.

Purchases by Subsidiaries

Under Irish law, an Irish or non-Irish subsidiary may purchase our ordinary shares either on market or off market. For one of our subsidiaries to make purchases on market of our ordinary shares, our shareholders must provide general authorization for such purchase by way of ordinary resolution. However, as long as this general authority has been granted, no specific shareholder authority for a particular on market purchase by a subsidiary of our ordinary shares is required. For a purchase by a subsidiary off market, the proposed purchase contract must be authorized by special resolution of our shareholders before the contract is entered into. The person whose ordinary shares are to be bought back cannot vote in favor of the special resolution and the purchase contract must be on display or must be available for inspection by our shareholders at our registered office from the date of the notice of the meeting at which the resolution approving the contract is to be proposed.

In order for one of our subsidiaries to make an on market purchase of our ordinary shares, such shares must be purchased on a "recognized stock exchange." Nasdaq is specified as a recognized stock exchange for this purpose by Irish law.

The number of ordinary shares held by our subsidiaries at any time will count as treasury shares and will be included in any calculation of the permitted treasury share threshold of 10% of the nominal value of our issued share capital. While a subsidiary holds any of our shares, it cannot exercise any voting rights in respect of those shares. The acquisition of our ordinary shares by a subsidiary must be funded out of distributable reserves of the subsidiary.

Lien on Shares, Calls on Shares and Forfeiture of Shares

Our Articles provide that we will have a first and paramount lien on every share that is not a fully paid share for all amounts payable at a fixed time or called in respect of that share. Subject to the terms of their allotment, directors may call for any unpaid amounts in respect of any shares to be paid, and if payment is not made, the shares may be forfeited. These provisions are customary in the articles of association of an Irish public company limited by shares such as our company and will only be applicable to shares that have not been fully paid.

Anti-Takeover Provisions

Business Combinations with Interested Shareholders

Our Articles include a provision similar to Section 203 of the Delaware General Corporation Law, which generally prohibits us from engaging in a business combination with an interested shareholder for a period of three years following the date the person became an interested shareholder, unless, in general:

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our board of directors approved the transaction which resulted in the shareholder becoming an interested shareholder;



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upon consummation of the transaction which resulted in the shareholder becoming an interested shareholder, the shareholder owned at least 85% of the voting shares outstanding at the time of commencement of such transaction, excluding for purposes of determining the number of voting shares outstanding (but not the outstanding voting shares owned by the interested shareholder), voting shares owned by persons who are directors and also officers and by certain employee share plans; or

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the business combination is approved by our board of directors and authorized at an annual or extraordinary general meeting of shareholders by the affirmative vote of the holders of at least 75% of the outstanding voting shares that are not owned by the interested shareholder.

A "business combination" is generally defined as a merger, asset or stock sale or other transaction resulting in a financial benefit to the interested shareholder. An "interested shareholder" is generally defined as a person who, together with affiliates and associates, owns or, within three years prior to the date in question, owned 15% or more of our outstanding voting shares.

Irish Takeover Rules and Substantial Acquisition Rules

A transaction in which a third party seeks to acquire 30% or more of our voting rights and any other acquisitions of our securities will be governed by the Irish Takeover Panel Act 1997 and the Irish Takeover Rules made thereunder, or the Irish Takeover Rules, and will be regulated by the Irish Takeover Panel. The "General Principles" of the Irish Takeover Rules and certain important aspects of the Irish Takeover Rules are described below.

General Principles

The Irish Takeover Rules are built on the following General Principles which will apply to any transaction regulated by the Irish Takeover Panel:

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in the event of an offer, all holders of securities of the target company must be afforded equivalent treatment and, if a person acquires control of a company, the other holders of securities must be protected;



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the holders of securities in the target company must have sufficient time and information to enable them to reach a properly informed decision on the offer; where it advises the holders of securities, the board of directors of the target company must give its views on the effects of the implementation of the offer on employment, employment conditions and the locations of the target company's place of business;



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a target company's board of directors must act in the interests of that company as a whole and must not deny the holders of securities the opportunity to decide on the merits of the offer;



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false markets must not be created in the securities of the target company, the bidder or any other company concerned by the offer in such a way that the rise or fall of the prices of the securities becomes artificial and the normal functioning of the markets is distorted;



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a bidder can only announce an offer after ensuring that he or she can fulfill in full the consideration offered, if such is offered, and after taking all reasonable measures to secure the implementation of any other type of consideration;



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a target company may not be hindered in the conduct of its affairs longer than is reasonable by an offer for its securities; and



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a "substantial acquisition" of securities, whether such acquisition is to be effected by one transaction or a series of transactions, shall take place only at an acceptable speed and shall be subject to adequate and timely disclosure.

Mandatory Bid

Under certain circumstances, a person who acquires shares, or other voting securities, of a company may be required under the Irish Takeover Rules to make a mandatory cash offer for the remaining outstanding voting securities in that company at a price not less than the highest price paid for the securities by the acquiror, or any parties acting in concert with the acquiror, during the previous 12 months. This mandatory bid requirement is triggered if an acquisition of securities would increase the aggregate holding of an acquiror, including the holdings of any parties acting in concert with the acquiror, to securities representing 30% or more of the voting rights in a company, unless the Irish Takeover Panel otherwise consents. An acquisition of securities by a person holding, together with its concert parties, securities representing between 30% and 50% of the voting rights in a company would also trigger the mandatory bid requirement if, after giving effect to the acquisition, the percentage of the voting rights held by that person, together

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with its concert parties, would increase by 0.05% within a 12-month period. Any person, excluding any parties acting in concert with the holder, holding securities representing more than 50% of the voting rights of a company is not subject to these mandatory offer requirements in purchasing additional securities.

Voluntary Bid; Requirements to Make a Cash Offer and Minimum Price Requirements

If a person makes a voluntary offer to acquire our outstanding ordinary shares, the offer price must not be less than the highest price paid for our ordinary shares by the bidder or its concert parties during the three-month period prior to the commencement of the offer period. The Irish Takeover Panel has the power to extend the "look back" period to 12 months if the Irish Takeover Panel, taking into account the General Principles, believes it is appropriate to do so.

If the bidder or any of its concert parties has acquired our ordinary shares (1) during the 12-month period prior to the commencement of the offer period that represent more than 10% of our total ordinary shares or (2) at any time after the commencement of the offer period, the offer must be in cash or accompanied by a full cash alternative and the price per ordinary share must not be less than the highest price paid by the bidder or its concert parties during, in the case of clause (1), the 12-month period prior to the commencement of the offer period or, in the case of (2), the offer period. The Irish Takeover Panel may apply this Rule to a bidder who, together with its concert parties, has acquired less than 10% of our total ordinary shares in the 12-month period prior to the commencement of the offer period if the Irish Takeover Panel, taking into account the General Principles, considers it just and proper to do so.

An offer period will generally commence from the date of the first announcement of the offer or proposed offer.

Substantial Acquisition Rules

The Irish Takeover Rules also contain rules governing substantial acquisitions of shares and other voting securities which restrict the speed at which a person may increase his or her holding of shares and rights over shares to an aggregate of between 15% and 30% of the voting rights of the company. Except in certain circumstances, an acquisition or series of acquisitions of shares or rights over shares representing 10% or more of the voting rights of the company is prohibited, if such acquisition(s), when aggregated with shares or rights already held, would result in the acquirer holding 15% or more but less than 30% of the voting rights of the company and such acquisitions are made within a period of seven days. These rules also require accelerated disclosure of acquisitions of shares or rights over shares relating to such holdings.

Frustrating Action

Under the Irish Takeover Rules, our board of directors is not permitted to take any action that might frustrate an offer for our shares once our board of directors has received an approach that may lead to an offer or has reason to believe that such an offer is or may be imminent, subject to certain exceptions. Potentially frustrating actions such as 1) the issue of shares, options, restricted share units or convertible securities, (2) material acquisitions or disposals, (3) entering into contracts other than in the ordinary course of business or (4) any action, other than seeking alternative offers, which may result in frustration of an offer, are prohibited during the course of an offer or at any earlier time during which our board of directors has reason to believe an offer is or may be imminent. Exceptions to this prohibition are available where:

§

the action is approved by our shareholders at a general meeting; or



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the Irish Takeover Panel has given its consent, where:



§

it is satisfied the action would not constitute frustrating action;



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our shareholders holding more than 50% of the voting rights state in writing that they approve the proposed action and would vote in favor of it at a general meeting;



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the action is taken in accordance with a contract entered into prior to the announcement of the offer, or any earlier time at which our board of directors considered the offer to be imminent; or



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the decision to take such action was made before the announcement of the offer and either has been at least partially implemented or is in the ordinary course of business.

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Shareholders' Rights Plan

Irish law does not expressly authorize or prohibit companies from issuing share purchase rights or adopting a shareholder rights plan as an anti-takeover measure. However, there is no directly relevant case law on the validity of such plans under Irish law. In addition, such a plan would be subject to the Irish Takeover Rules and the General Principles underlying the Irish Takeover Rules. Our Articles allow our board of directors to adopt a shareholder rights plan upon such terms and conditions as our board of directors deems expedient and in the best interests of us, subject to applicable law.

Subject to the Irish Takeover Rules, our board of directors also has power to issue any of our authorized and unissued shares on such terms and conditions as it may determine and any such action should be taken in our best interests. It is possible, however, that the terms and conditions of any issue of preferred shares could discourage a takeover or other transaction that holders of some or a majority of the ordinary shares believe to be in their best interests or in which holders might receive a premium for their shares over the then-market price of the shares.

Disclosure of Interests in Shares

Under the Irish Companies Act, our shareholders must notify us if, as a result of a transaction, the shareholder will become interested in three percent or more of our voting shares, or if as a result of a transaction a shareholder who was interested in three percent or more of our voting shares ceases to be so interested. Where a shareholder is interested in three percent or more of our voting shares, the shareholder must notify us of any alteration of his or her interest that brings his or her total holding through the nearest whole percentage number, whether an increase or a reduction. The relevant percentage figure is calculated by reference to the aggregate nominal value of the voting shares in which the shareholder is interested as a proportion of the entire nominal value of our issued share capital (or any such class of share capital in issue). Where the percentage level of the shareholder's interest does not amount to a whole percentage, this figure may be rounded down to the next whole number. We must be notified within five business days of the transaction or alteration of the shareholder's interests that gave rise to the notification requirement. If a shareholder fails to comply with these notification requirements, the shareholder's rights in respect of any of our shares it holds will not be enforceable, either directly or indirectly. However, such person may apply to the High Court of Ireland to have the rights attaching to such shares reinstated.

In addition to these disclosure requirements, we, under the Irish Companies Act, may, by notice in writing, require a person whom we know or have reasonable cause to believe to be, or at any time during the three years immediately preceding the date on which such notice is issued to have been, interested in shares comprised in our relevant share capital to (i) indicate whether or not it is the case and (ii) where such person holds or has during that time held an interest in our shares, to provide additional information, including the person's own past or present interests in our shares. If the recipient of the notice fails to respond within the reasonable time period specified in the notice, we may apply to the Irish court for an order directing that the affected shares be subject to certain restrictions, as prescribed by the Irish Companies Act, as follows:

§

any transfer of those shares or, in the case of unissued shares, any transfer of the right to be issued with shares and any issue of shares, shall be void;



§

no voting rights shall be exercisable in respect of those shares;



§

no further shares shall be issued in right of those shares or in pursuance of any offer made to the holder of those shares; and



§

no payment shall be made of any sums due from us on those shares, whether in respect of capital or otherwise.

The court may also order that shares subject to any of these restrictions be sold with the restrictions terminating upon the completion of the sale.

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In the event we are in an offer period pursuant to the Irish Takeover Rules, accelerated disclosure provisions apply for persons holding an interest in our securities of one percent or more.

Listing

Our ordinary shares are listed on The Nasdaq Global Select Market under the symbol "SBBP."

Transfer Agent and Registrar

The transfer agent and registrar for our ordinary shares is Computershare, Inc. The transfer agent and registrar's address is 480 Washington Blvd., 26^th Floor, Jersey City, NJ 07310.

Differences in Corporate Law Between Ireland and the State of Delaware

As a public limited company incorporated under the laws of Ireland, the rights of our shareholders are governed by applicable Irish law, including the Irish Companies Act, and not by the law of any U.S. state. As a result, our directors and shareholders are subject to different responsibilities, rights and privileges than are applicable to directors and shareholders of U.S. corporations. We have set below a summary of the differences between the provisions of the Irish Companies Act applicable to us and the Delaware General Corporation Law relating to stockholders' rights and protections. This summary is not intended to be a complete discussion of the respective rights and it is qualified in its entirety by reference to Irish law, Delaware law and our Articles. Before investing, you should consult your legal advisor regarding the impact of Irish law on your specific circumstances and reasons for investing. The summary below does not include a description of rights or obligations under the U.S. federal securities laws or NASDAQ listing requirements. You are also urged to carefully read the relevant provisions of the Delaware General Corporation Law and the Irish Companies Act for a more complete understanding of the differences between Delaware and Irish law.

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DILUTION

If you invest in our ordinary shares in this offering, your ownership interest will be immediately diluted to the extent of the difference between the public offering price per ordinary share and the as adjusted net tangible book value per ordinary share immediately after this offering.

At June 30, 2020, we had a net tangible book value of approximately $18.0 million, corresponding to a net tangible book value of $0.33 per ordinary share, based upon 54,355,957 ordinary shares outstanding as of that date. Net tangible book value per ordinary share represents the amount of our total assets less our total liabilities, excluding intangible assets, divided by the total number of our ordinary shares outstanding at such date.

After giving effect to the sale of 11,111,111 ordinary shares in this offering at the offering price of $2.25 per share, and after deducting underwriting discounts and commissions and estimated offering expenses payable by us, our as adjusted net tangible book value as of June 30, 2020 would have been approximately $41.1 million, or $0.63 per ordinary share. This amount represents an immediate increase in as adjusted net tangible book value of $0.30 per share to our existing shareholders, and an immediate dilution in adjusted net tangible book value of $1.62 per share to new investors purchasing shares of ordinary shares in this offering.

Dilution in net tangible book value per share represents the difference between the amount per share of our ordinary shares paid by purchasers in this offering and the as adjusted net tangible book value per ordinary share after this offering. The following table illustrates this dilution:

The foregoing discussion and table do not take into account further dilution to new investors that could occur upon the exercise of the underwriters' option to purchase up to an additional 1,666,666 ordinary shares within 30 days of the date of this prospectus supplement. If the underwriters exercise in full their option to purchase additional shares, the as adjusted net tangible book value per ordinary share after giving effect to the offering would be $0.67 per ordinary share, the increase in the net tangible book value per ordinary share to existing shareholders would be $0.34 per ordinary share and the dilution to new investors would be $1.58 per ordinary share.

The number of ordinary shares shown above to be outstanding after this offering is based on 54,355,957 ordinary shares outstanding as of June 30, 2020, and excludes:

§

10,499,222 ordinary shares issuable upon the exercise of stock options outstanding as of June 30, 2020, with a weighted-average exercise price of $5.28 per ordinary share;



§

7,100,643 ordinary shares issuable upon the exercise of warrants outstanding as of June 30, 2020, with a weighted-average exercise price of $4.06 per ordinary share;



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1,090,300 ordinary shares issuable upon the vesting of 1,090,300 restricted stock units outstanding as of June 30, 2020;

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71,029 ordinary shares reserved for future issuance under our Non-Employee Director Equity Compensation Plan as of June 30, 2020;



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332,429 ordinary shares reserved for future issuance under our 2015 Equity Compensation Plan as of June 30, 2020;



§

1,373,903 ordinary shares reserved for future issuance under our 2017 Inducement Plan as of June 30, 2020;



§

shares issuable upon the conversion of up to $3.0 million of the aggregate principal amount of any loans outstanding under the term loan agreement with Avenue, at Avenue's discretion, at a price per share equal to the lower of (a) $2.24, or (b) 20% above the effective price of any bona fide equity financing prior to December 31, 2020;



§

18,000 ordinary shares issuable upon the exercise of stock options outstanding, which were granted after June 30, 2020 with a weighted average exercise price of $3.99 per ordinary share;



§

315,000 ordinary shares issuable upon the vesting of 315,000 restricted stock units outstanding, which were granted after June 30, 2020; and



§

1,400,000 ordinary shares issued under our Equity Distribution Agreement with JMP Securities LLC since June 30, 2020.

In addition, we may choose to raise additional capital due to market conditions or strategic considerations, even if we believe we have sufficient funds for our current or future operating plans. To the extent that we raise additional capital by issuing equity securities or convertible debt, your ownership will be further diluted.

To the extent that any outstanding options or warrants are exercised, outstanding restricted stock units vest, new options or restricted stock units are issued under our share-based compensation plans or we are required to issue additional warrants to Avenue, pursuant to the terms of our term loan agreement with Avenue, there will be further dilution to investors participating in this offering.

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TAXATION

The following summary contains a description of the material Irish and U.S. federal income tax consequences of the acquisition, ownership and disposition of our ordinary shares, but it does not purport to be a comprehensive description of all the tax considerations that may be relevant. The summary is based upon the tax laws of Ireland and regulations thereunder and on the tax laws of the United States and regulations thereunder as of the date hereof, which are subject to change.

The tax consequences to you of an investment in our ordinary shares will depend, in part, on your own tax circumstances. You are urged to consult with your own tax advisor about the federal, state, local and foreign tax consequences particular to your circumstances.

Irish Tax Considerations

Scope of Discussion

The following is a summary of the material Irish tax considerations applicable to certain investors who are the beneficial owners of our ordinary shares. This summary is based on existing Irish tax law and our understanding of the practices of the Irish Revenue Commissioners in effect on the date of this prospectus supplement. Legislative, administrative or judicial changes may modify the tax consequences described in this summary, possibly with retroactive effect. Furthermore, we can provide no assurances that the tax consequences contained in this summary will not be challenged by the Irish Revenue Commissioners or will be sustained by an Irish court if they were to be challenged.

This summary does not constitute tax advice and is intended only as a general guide. This summary is not exhaustive and shareholders should consult their own tax advisers about the Irish tax consequences (and the tax consequences under the laws of other relevant jurisdictions), which may arise as a result of being a shareholder in our company including the acquisition, ownership and disposal of our ordinary shares. Furthermore, this summary applies only to shareholders who will hold our ordinary shares as capital assets and does not apply to all categories of shareholders, such as dealers in securities, trustees, insurance companies, collective investment schemes, pension funds or shareholders who have, or who are deemed to have, acquired their shares by virtue of an office or employment performed or carried on in Ireland.

Irish Tax on Chargeable Gains

Non-Resident Shareholders

The current rate of tax on chargeable gains (where applicable) in Ireland is 33%.

Shareholders who are not residents or ordinarily residents in Ireland for Irish tax purposes should not be liable to Irish tax on chargeable gains realized on a disposal of our ordinary shares unless such shares are used, held or acquired for the purpose of a trade or business carried on by such a shareholder in Ireland through a branch or an agency.

A shareholder who is an individual and who is temporarily not resident in Ireland may, under Irish anti-avoidance legislation, still be liable to Irish tax on any chargeable gain realized on a disposal of our ordinary shares during the period in which the individual is a non-resident.

Irish Dividend Withholding Tax

Our company does not anticipate paying dividends for the foreseeable future. However, if in the future we were to pay a dividend or make a distribution to our shareholders, that distribution may be subject to dividend withholding tax, or DWT, at the standard rate of Irish income tax (currently 25%) unless one of the exemptions described below applies.

For DWT and Irish income tax purposes, a dividend includes any distribution made to shareholders, including cash dividends, non-cash dividends and any additional shares taken in lieu of a cash dividend. Where an exemption from DWT does not apply in respect of a distribution made to a particular shareholder,

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we are responsible for withholding DWT at source in respect of the distributions made and remitting the tax withheld to the Irish Revenue Commissioners.

General Exemptions

Certain shareholders, both individual and corporate, are entitled to an exemption from DWT. In particular, dividends paid to a non-Irish resident shareholder will not be subject to DWT where the shareholder is beneficially entitled to the dividend and is:

§

an individual shareholder that is resident for tax purposes in a "relevant territory" (including the United States) and the individual is neither resident nor ordinarily resident in Ireland;



§

a corporate shareholder that is resident for tax purposes in a "relevant territory" (including the United States), and is not under the control, whether directly or indirectly, of a person or persons who is or are resident in Ireland;



§

a corporate shareholder that is not resident for tax purposes in Ireland and that is ultimately controlled, directly or indirectly, by persons resident in a "relevant territory" (including the United States) and who is not controlled, directly or indirectly, by persons who are not resident in a "relevant territory";



§

a corporate shareholder that is not a resident for tax purposes in Ireland and whose principal class of shares, or those of its 75% direct or indirect parent, is substantially and regularly traded on a stock exchange in Ireland, on a recognized share exchange in a "relevant territory" or on such other share exchange as may be approved by the Irish Minister for Finance; or



§

a corporate shareholder that is not resident for tax purposes in Ireland and is wholly-owned, directly or indirectly, by two or more companies where the principal class of shares of each of such companies is substantially and regularly traded on a stock exchange in Ireland, on a recognized share exchange in a "relevant territory" or on such other share exchange as may be approved by the Irish Minister for Finance;

and provided, in all cases noted above (but subject to "Shares Held by U.S. Resident Shareholders" below), Strongbridge Biopharma plc or, in respect of Strongbridge Biopharma plc shares held through a Depositary Trust Company, or DTC, any qualifying intermediary appointed by Strongbridge Biopharma plc, has received from the shareholder, where required, the relevant Irish DWT declaration forms prior to the payment of the dividend. In practice, in order to ensure sufficient time to process the receipt of relevant Irish DWT declaration forms, the Strongbridge Biopharma plc shareholder where required should furnish the relevant Irish DWT declaration forms to:

§

its broker (and the relevant information is further transmitted to any qualifying intermediary appointed by Strongbridge Biopharma plc) before the record date for the dividend (or such later date before the dividend payment date as may be notified to the shareholder by the broker) if its shares are held through DTC; or



§

Strongbridge Biopharma plc's transfer agent at least seven business days before the record date for the dividend if its shares are held outside of DTC.

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A list of "relevant territories" for the purposes of DWT (as of the date of this prospectus supplement), is set forth below and this list is subject to change:

It is the responsibility of each individual shareholder to determine whether or not they are a "resident" for tax purposes in a "relevant territory."

Irish DWT declaration forms are available at: http://www.revenue.ie/en/tax/dwt/forms/index.html. The information on such website does not constitute a part of, and is not incorporated by reference into, this prospectus supplement.

Prior to paying any future dividend, our company will enter into an agreement with an institution which is recognized by the Irish Revenue Commissioners as a "qualifying intermediary" and which satisfies the requirements for dividends to be paid to certain shareholders free from DWT where such shareholders hold their shares through DTC, as described below. The agreement will generally provide for certain arrangements relating to distributions in respect of those shares that are held through DTC, which are referred to as the "deposited securities".. The agreement will provide that the "qualifying intermediary" shall distribute or otherwise make available to Cede & Co., as nominee for DTC, any cash dividend or other cash distribution to be made to holders of the deposited securities, after we deliver or cause to be delivered to the "qualifying intermediary" the cash to be distributed.

We will rely on the information received directly or indirectly from brokers and their transfer agent in determining where shareholders reside and whether they have furnished the required U.S. tax information, as described below, and whether they have provided the required Irish DWT declaration forms. Shareholders who are required to furnish Irish DWT declaration forms in order to receive their dividends without DWT should note that those declarations forms are only valid until 31 December of the fifth year after the year of issue/certification of the forms and new DWT declarations forms must be completed and filed before the expiration of that period to enable the shareholder continue to receive dividends without DWT.

Shares Held by U.S. Resident Shareholders

Dividends paid on our ordinary shares that are owned by residents of the United States should not be subject to DWT, subject to the completion and delivery of the relevant forms to us.

Residents of the United States who hold their shares through DTC should be entitled to receive dividends without DWT provided that the address of the beneficial owner of the shares in the records of the broker holding such shares is in the United States (and such broker has further transmitted the relevant information to a qualifying intermediary appointed by us). We would strongly recommend that such

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shareholders ensure that their information has been properly recorded by their brokers so that such brokers can further transmit the relevant information to a qualifying intermediary appointed by us.

Residents of the United States who hold their shares outside of DTC will be entitled to receive dividends without DWT provided that the shareholder has completed the relevant Irish DWT declaration form and this declaration form remains valid. Such shareholders must provide the relevant Irish DWT declaration form to our transfer agent at least seven business days before the record date of the dividend payment to which they are entitled. We would strongly recommend that such shareholders complete the relevant Irish DWT declaration form and provide them to our transfer agent as soon as possible after acquiring shares in our company.

If a U.S. resident shareholder is entitled to an exemption from DWT, but receives a dividend subject to DWT, that shareholder may be entitled to claim a refund of DWT from the Irish Revenue Commissioners, subject to certain time limits and provided the shareholder is beneficially entitled to the dividend.

Shares Held by Residents of "Relevant Territories" Other Than the United States

Shareholders who are residents of "relevant territories" other than the United States, and who are entitled to one of the exemptions from DWT referred to above under the heading "General Exemptions", must complete the relevant Irish DWT declaration form in order to receive dividends without DWT.

Shareholders must provide the relevant Irish DWT declaration form to their brokers so that such brokers can further transmit the relevant information to a qualifying intermediary appointed by us before the record date of the dividend to which they are entitled, in the case of shares held through DTC, or to our transfer agent at least seven business days before such record date, in the case of shares held outside of DTC. We would strongly recommend that such shareholders complete the relevant Irish DWT declaration form and provide that form to their brokers or our transfer agent as soon as possible after acquiring shares in our company.

If a shareholder who is resident in a "relevant territory" and is entitled to an exemption from DWT receives a dividend subject to DWT, that shareholder may be entitled to claim a refund of DWT from the Irish Revenue Commissioners, subject to certain time limits and provided the shareholder is beneficially entitled to the dividend.

Notwithstanding the foregoing, the General Exemptions from DWT referred to above do not apply to an individual shareholder that is resident or ordinarily resident in Ireland or to a corporate entity that is resident in Ireland or that is under the control, whether directly or indirectly, of a person or persons who is or who are resident in Ireland. However, other exemptions from DWT may still be available to such shareholder.

In addition, it may also be possible for certain shareholders to rely on a double tax treaty to limit the applicable DWT.

Shares Held by Other Persons

A shareholder that does not fall within one of the categories specifically mentioned above may nonetheless fall within other exemptions from DWT provided that the shareholder has completed the relevant Irish DWT declaration form and this declaration form remains valid.

If any such shareholder is exempt from DWT but receives a dividend subject to DWT, that shareholder may be entitled to claim a refund of DWT from the Irish Revenue Commissioners, subject to certain time limits.

Distributions paid in respect of our shares held through DTC that are owned by a partnership formed under the laws of a "relevant territory" and where all the underlying partners are resident in a "relevant territory" will be entitled to exemption from DWT if all of the partners complete the appropriate Irish DWT declaration forms and provide them to their brokers (so that such brokers can further transmit the relevant information to a qualifying intermediary appointed by us) before the record date for the distribution (or such later date before the distribution payment date as may be notified to the shareholder by the broker) If any partner is

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not a resident of a "relevant territory", no part of the partnership's position is entitled to exemption from DWT.

Income Tax on Dividends Paid

Irish income tax may arise for certain shareholders in respect of any dividends received from us.

Non-Irish Resident Shareholders

A shareholder that is not resident or ordinarily resident in Ireland for Irish tax purposes and who is entitled to an exemption from DWT generally has no liability to Irish income tax or other similar charges with respect to any dividends received from us. An exception to this position may apply where a shareholder holds our ordinary shares through a branch or agency in Ireland through which a trade is carried on.

A shareholder that is not resident or ordinarily resident in Ireland for Irish tax purposes and who is not entitled to an exemption from DWT generally has no additional liability to Irish income tax or other similar charges on any dividends received from us. In these circumstances, the shareholder's liability to Irish tax is effectively limited to the amount of DWT withheld by us. An exception to this position may apply where a shareholder holds our ordinary shares through a branch or an agency in Ireland through which a trade is carried on.

Capital Acquisitions Tax

Capital acquisitions tax, or CAT, consists principally of gift tax and inheritance tax. A gift or inheritance of our ordinary shares, including where such shares are held in DTC, may attract a charge to CAT irrespective of the place of residence, ordinary residence or domicile of the transferor or the transferee of the shares. This is because a charge to CAT may arise on a gift or inheritance which comprises of property situated in Ireland. Our ordinary shares are regarded as property situated in Ireland for CAT purposes because our share register must be retained in Ireland. The person who receives the gift or inheritance is primarily liable for any CAT that may arise.

CAT is levied at a rate of 33% above certain tax-free thresholds. The appropriate tax-free threshold is dependent upon (1) the relationship between the donor and the donee and (2) the aggregation of the values of previous gifts and inheritances received by the donee from persons within the same group threshold. Gifts and inheritances passing between spouses are exempt from CAT, as are gifts to certain charities. Shareholders should consult their own tax advisers as to whether CAT is creditable or deductible in computing any domestic tax liabilities.

Irish Stamp Duty

The rate of Irish stamp duty, where applicable, on the transfer of shares in an Irish incorporated company is 1% of the price paid or the market value of the shares acquired, whichever is greater. Where a charge to Irish stamp duty applies it is generally a liability for the transferee. However, in the case of a gift or transfer at less than fair market value, all parties to the transfer are jointly and severally liable. Irish stamp duty may, depending on the manner in which our ordinary shares are held, be payable in respect of the transfer of our ordinary shares.

Shares held through DTC

On the basis that most of our shares are expected to be held through DTC, or through brokers who hold shares on behalf of their customers through DTC, the transfer of such shares should be exempt from Irish stamp duty based on established practice of Irish Revenue Commissioners. We received written confirmation from the Irish Revenue Commissioners on June 22, 2015 that a transfer of our shares held through DTC and transferred by means of a book-entry interest would be exempt from Irish stamp duty.

Shares Held Outside of DTC or Transferred Into or Out of DTC

A transfer of our ordinary shares where any of the parties to the transfer hold the shares outside of DTC may be subject to Irish stamp duty. A shareholder should be entitled to transfer our ordinary shares into, or out of, DTC without giving rise to Irish stamp duty provided (1) there is no change in beneficial ownership of

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the shares and (2) the transfer into, or out of, DTC, is not effected in contemplation of a subsequent sale of such shares by the beneficial owner to a third party.

To avoid Irish stamp duty on transfers of our ordinary shares any directly registered shareholder may wish to consider opening a broker account, and any person who wishes to acquire our ordinary shares may wish to consider holding such shares through DTC.

DTC Requirement

In order for DTC, Cede & Co. and National Securities Clearing Corporation, or NSCC, which provides clearing services for securities that are eligible for the depository and book-entry transfer services provided by DTC and registered in the name of Cede & Co., which entities are referred to collectively as the DTC Parties, to agree to provide services with respect to our ordinary shares, we have entered into a composition agreement with the Irish Revenue Commissioners under which we have agreed to pay or procure the payment of any obligation for any Irish stamp duty or similar Irish transfer or documentary tax with respect to our ordinary shares, on (1) transfers to which any of the DTC Parties is a party or (2) which may be processed through the services of any of the DTC Parties and the DTC Parties have received confirmation from the Irish Revenue Commissioners that during the period that such composition agreement remains in force, the DTC Parties shall not be liable for any Irish stamp duty with respect to our ordinary shares.

In addition, to assure the DTC Parties that they will not be liable for any Irish stamp duty or similar Irish transfer or documentary tax with respect to our ordinary shares under any circumstances, including as a result of a change in applicable law, and to make other provisions with respect to our ordinary shares required by the DTC Parties, we and our transfer agent have entered into a Special Eligibility Agreement for Securities with DTC, Cede & Co. and NSCC, or the DTC Eligibility Agreement.

The DTC Eligibility Agreement provides for certain indemnities of the DTC Parties by us and Computershare, Inc. (as to which we indemnify Computershare, Inc.) and provides that DTC may impose a global lock on our ordinary shares or otherwise limit transactions in the shares, or cause the shares to be withdrawn, and NSCC may, in its sole discretion, exclude our ordinary shares from its continuous net settlement service or any other service, and any of the DTC Parties may take other restrictive measures with respect to our ordinary shares as it may deem necessary and appropriate, without any liability on the part of any of the DTC Parties, (1) at any time that it may appear to any of the DTC Parties, in any such party's sole discretion, that to continue to hold or process transactions in our ordinary shares will give rise to any Irish stamp duty or similar Irish transfer or documentary tax liability with respect to our ordinary shares on the part of any of the DTC Parties or (2) otherwise as DTC's rules or NSCC's rules provide.

Notwithstanding our entry into a composition agreement with the Irish Revenue Commissioners and the indemnities given pursuant to the DTC Eligibility Agreement, any stamp duty liability resulting from a transfer of our shares will be for the "accountable person" under Irish law (generally the transferee) and, to the extent we or a subsidiary of our company discharges such liability, on any transferee's behalf, we will seek payment or reimbursement of such liability.

THE IRISH TAX CONSIDERATIONS SUMMARIZED ABOVE ARE FOR GENERAL INFORMATION ONLY. EACH SHAREHOLDER SHOULD CONSULT HIS OR HER OWN TAX ADVISOR AS TO THE PARTICULAR TAX CONSEQUENCES THAT MAY APPLY TO SUCH SHAREHOLDER.

Material U.S. Federal Income Tax Considerations for U.S. Holders

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consequences that may be relevant in light of the U.S. Holder's particular circumstances, including alternative minimum tax consequences and the Medicare net investment income tax, any state or local tax considerations, any U.S. federal gift, estate or generation-skipping transfer tax consequences and tax consequences applicable to U.S. Holders subject to special rules, such as:

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certain financial institutions;



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brokers;



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dealers or traders in securities who use a mark-to-market method of tax accounting;



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real estate investment trusts;



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insurance companies;



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persons holding ordinary shares as part of a hedging transaction, straddle, wash sale, conversion transaction or integrated transaction or persons entering into a constructive sale with respect to the ordinary shares;



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regulated investment companies;



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persons whose functional currency for U.S. federal income tax purposes is not the U.S. dollar;



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entities classified as partnerships or other pass-through entities for U.S. federal income tax purposes, including persons that will hold our ordinary shares through such an entity;



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tax-exempt entities, including an "individual retirement account" or "Roth IRA;"



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persons that own, directly, indirectly or through attribution, ten percent or more of our voting power or value;



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persons that are U.S. expatriates;



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persons subject to section 451(b) of the Code;



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persons who acquired our ordinary shares pursuant to the exercise of an employee stock option or otherwise as compensation; or



§

persons holding shares in connection with a trade or business conducted outside of the United States.

If an entity or arrangement that is classified as a partnership for U.S. federal income tax purposes holds ordinary shares, the U.S. federal income tax consequences relating to an investment in the ordinary shares will depend in part upon the status and activities of such entity or arrangement and the particular partners thereof. Any such entity or arrangement, and partners in such entities or arrangements, should consult their tax advisers as to their particular U.S. federal income tax consequences of holding and disposing of the ordinary shares.

This discussion is based on the Code, administrative pronouncements, judicial decisions, and final, temporary and proposed U.S. Treasury regulations, all as of the date hereof, any of which is subject to change, possibly with retroactive effect.

As used in this discussion, a "U.S. Holder" is a holder who, for U.S. federal income tax purposes, is a beneficial owner of ordinary shares who is:

§

an individual who is a citizen or resident of the United States;



§

a corporation, or other entity taxable as a corporation, created or organized in or under the laws of the United States, any state therein or the District of Columbia;



§

an estate whose income is includible in gross income for U.S. federal income tax purposes regardless of its source; or



§

a trust if (1) a U.S. court is able to exercise primary supervision over the administration of the trust and one or more U.S. persons have authority to control all substantial decisions of the trust or (2) the trust has a valid election in effect under applicable Treasury Regulations to be treated as a U.S. person.

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U.S. Holders should consult their tax advisers concerning the U.S. federal, state, local and foreign tax consequences of owning and disposing of ordinary shares in their particular circumstances.

Passive Foreign Investment Company Rules

In general, a non-U.S. corporation will be considered a passive foreign investment company, or a PFIC, for any taxable year in which (1) 75% or more of its gross income consists of passive income or (2) 50% or more of the average quarterly value of its assets consists of assets that produce, or are held for the production of, passive income. For purposes of the above calculations, a non-U.S. corporation that directly or indirectly owns at least 25% by value of the shares of another corporation is treated as if it held its proportionate share of the assets of the other corporation and received directly its proportionate share of the income of the other corporation. Passive income generally includes, among other things, dividends, interest, rents, royalties and certain gains from the sale or exchange of property that gives rise to passive income. Assets that produce or are held for the production of passive income generally include cash, even if held as working capital or raised in a public offering, marketable securities, and other assets that may produce passive income.

Our status as a PFIC will depend on the nature and composition of our income and the nature, composition and value of our assets (which will generally be determined based on the fair market value of each asset, with the value of goodwill and going concern value being determined in large part by reference to the market value of the ordinary shares, which may be volatile). Based on an analysis of the value of our assets, including any goodwill, and the nature and composition of our income, we believe that we were not a PFIC for our taxable year ending December 31, 2019 and that we will not be classified as a PFIC for our current taxable year ending December 31, 2020. We note, however, that our determination is not binding on the Internal Revenue Service, and it is possible that the Internal Revenue Service will take the position that we are properly classified as a PFIC in either or both such years. In addition, we may be classified as a PFIC in future taxable years. We must determine our PFIC status annually based on tests which are factual in nature, and our status will depend on our income, assets and activities each year.

If we are a PFIC for any taxable year during which a U.S. Holder holds our ordinary shares, the U.S. Holder could be liable for additional taxes and interest charges under the PFIC "excess distribution" regime upon (i) a distribution paid during a taxable year that is greater than 125% of the average annual distributions paid in the three preceding taxable years, or, if shorter, the U.S. Holder's holding period for the ordinary shares, and (ii) any gain recognized on a sale, exchange or other disposition, including a pledge, of the ordinary shares, whether or not we continue to be a PFIC. Under the PFIC excess distribution regime, the tax on such distribution or gain would be determined by allocating the distribution or gain ratably over the U.S. Holder's holding period for the ordinary shares. The amounts allocated to the taxable year in which the distribution occurs or the gain is recognized and to years before we became a PFIC will be taxed as ordinary income. The amounts allocated to each other taxable year will be subject to tax at the highest rate in effect for that taxable year for individuals or corporations, as appropriate, applicable to ordinary income, and an interest charge will be imposed on the tax attributable to the allocated amounts.

If we are a PFIC for any year during which a U.S. Holder holds ordinary shares, we generally will continue to be treated as a PFIC with respect to the holder for all succeeding years during which the U.S. Holder holds ordinary shares, even if we cease to meet the threshold requirements for PFIC status, unless we cease to meet the requirements for PFIC status and the U.S. Holder makes a "deemed sale" election with respect to the ordinary shares. U.S. Holders should consult their tax advisers regarding the potential availability of a "deemed sale" election that would allow them to eliminate this continuing PFIC status under certain circumstances.

If we are a PFIC for any taxable year during which a U.S. Holder holds ordinary shares, and one of our non-U.S. corporate subsidiaries is also a PFIC (i.e., a lower tier PFIC), such U.S. Holder would be treated as owning a proportionate amount (by value) of the shares of the lower tier PFIC and would be taxed under the PFIC excess distribution regime on distributions by the lower tier PFIC and on gain from the disposition of

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shares of the lower tier PFIC even though such U.S. Holder would not receive the proceeds of those distributions or dispositions. Each U.S. Holder is advised to consult its tax advisors regarding the application of the PFIC rules to our non-U.S. subsidiaries.

If the ordinary shares are "regularly traded" on a "qualified exchange," a U.S. Holder may make a mark-to-market election that would result in tax treatment different from the general tax treatment for PFICs described above. The ordinary shares will be treated as "regularly traded" in any calendar year in which more than a de minimis quantity of the ordinary shares is traded on a qualified exchange on at least 15 days during each calendar quarter. The ordinary shares are listed on the Nasdaq Global Select Market, which is a qualified exchange for this purpose. U.S. If a mark-to-market election is in effect, a U.S. Holder generally would take into account, as ordinary income for each taxable year of the U.S. Holder, the excess of the fair market value of the ordinary shares held at the end of such taxable year over the adjusted tax basis of such ordinary shares. The U.S. Holder would also take into account, as an ordinary loss each year, the excess of the adjusted tax basis of such ordinary shares over their fair market value at the end of the taxable year, but only to the extent of the excess of amounts previously included in income over ordinary losses deducted as a result of the mark-to-market election. The U.S. Holder's tax basis in ordinary shares would be adjusted to reflect any income or loss recognized as a result of the mark-to-market election. Any gain from a sale, exchange or other disposition of ordinary shares in any taxable year in which we are a PFIC would be treated as ordinary income and any loss from such sale, exchange or other disposition would be treated first as ordinary loss (to the extent of any net mark-to-market gains previously included in income) and thereafter as capital loss.

A mark-to-market election will not apply to ordinary shares for any taxable year during which we are not a PFIC, but will remain in effect with respect to any subsequent taxable year in which we become a PFIC. Such election will not apply to any of our non-U.S. subsidiaries. Accordingly, a U.S. Holder may continue to be subject to tax under the PFIC excess distribution regime with respect to any of our lower-tier PFICs as described above, notwithstanding the U.S. Holder's mark-to-market election for the ordinary shares. U.S. Holders should consult their tax advisers regarding the availability and advisability of making a mark-to-market election in their particular circumstances.

Alternatively, a U.S. Holder can make an election, if we provide the necessary information, to treat us and each lower-tier PFIC as a qualified electing fund, a QEF Election, in the first taxable year that we are treated as a PFIC with respect to the U.S. Holder. A U.S. Holder must make the QEF Election for each PFIC by attaching a separate properly completed IRS Form 8621 for each PFIC to the U.S. Holder's timely filed U.S. federal income tax return. U.S. Holders should be aware that there can be no assurances that we will satisfy the record keeping requirements that apply to a QEF, or that we will supply U.S. Holders with information that such U.S. Holders are required to report under the QEF rules, in the event that we are a PFIC. Thus, U.S. Holders may not be able to make a QEF Election with respect to their ordinary shares. Further, no assurance can be given that such QEF information will be available for any lower-tier PFICs. Each U.S. Holder should consult its own tax advisers regarding the availability of, and procedure for making, a QEF Election.

If a U.S. Holder makes a QEF Election with respect to a PFIC, the holder will be taxed on a current basis on its pro rata share of the PFIC's ordinary earnings and net capital gain (at ordinary income and capital gain rates, respectively) for each taxable year that the entity is classified as a PFIC and for which the QEF election is in place and properly maintained. If a U.S. Holder makes a QEF Election with respect to us, any distributions paid by us out of our earnings and profits that were previously included in the U.S. Holder's income under the QEF Election would not be taxable to the U.S. Holder. A U.S. Holder will increase its tax basis in its ordinary shares by an amount equal to any income included under the QEF Election and will decrease its tax basis by any amount distributed on the ordinary shares that is not included in the U.S. Holder's income. In addition, a U.S. Holder will recognize capital gain or loss on the disposition of ordinary shares in an amount equal to the difference between the amount realized and the U.S. Holder's adjusted

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tax basis in the ordinary shares. U.S. Holders should note that if they make QEF Elections with respect to us and lower-tier PFICs, they may be required to pay U.S. federal income tax with respect to their ordinary shares for any taxable year significantly in excess of any cash distributions received on the shares for such taxable year. U.S. Holders should consult their tax advisers regarding making QEF Elections in their particular circumstances.

If we are a PFIC for any taxable year during which a U.S. Holder holds ordinary shares, such U.S. Holder would be required to file an annual information report with such U.S. Holder's U.S. Federal income tax return on IRS Form 8621.

U.S. Holders should consult their tax advisers concerning our PFIC status and the tax considerations relevant to an investment in a PFIC.

Taxation of Distributions

Subject to the PFIC rules described above, a U.S. Holder that receives distributions on ordinary shares, other than certain pro rata distributions of ordinary shares, will be required to include the gross amount of such distributions (before reduction for any amounts withheld in respect of French withholding tax) in income as a dividend when actually or constructively received to the extent of the U.S. Holder's pro rata share of our current or accumulated earnings and profits (as determined under U.S. federal income tax principles). Distributions in excess of earnings and profits will be nontaxable to the U.S. Holder to the extent of, and will be applied against and reduce (but not below zero), the U.S. Holder's adjusted tax basis in the ordinary shares. Distributions in excess of earnings and profits and such adjusted tax basis will generally be taxable to the U.S. Holder as described below under "Sale or other Disposition of Ordinary Shares." However, because we do not maintain calculations of our earnings and profits under U.S. federal income tax principles, it is expected that distributions generally will be reported to U.S. Holders as dividends. The amount of the dividend will be treated as foreign-source dividend income to U.S. Holders and will not be eligible for the dividends-received deduction generally available to U.S. corporations under the Code. The amount of any dividend income paid in Euros will be the U.S. dollar amount calculated by reference to the exchange rate in effect on the date of actual or constructive receipt, regardless of whether the payment is in fact converted into U.S. dollars. If the dividend is converted into U.S. dollars on the date of actual or constructive receipt, a U.S. Holder should not be required to recognize foreign currency gain or loss in respect of the dividend income. A U.S. Holder may have foreign currency gain or loss if the dividend is converted into U.S. dollars after the date of actual or constructive receipt, which foreign currency gain or loss will be "U.S. source" ordinary income or loss.

Dividends paid by a "qualified foreign corporation" are eligible for taxation to non-corporate U.S. Holders at a reduced capital gains rate rather than the marginal tax rates generally applicable to ordinary income provided that certain requirements are met, including holding period and the absence of certain risk reduction transaction requirements. A non-United States corporation (other than a corporation that is classified as a PFIC for the taxable year in which the dividend is paid or the preceding taxable year) generally will be considered to be a qualified foreign corporation (a) if it is eligible for the benefits of a comprehensive tax treaty with the United States which the Secretary of Treasury of the United States determines is satisfactory for purposes of this provision and which includes an exchange of information provision, or (b) with respect to any dividend it pays on ordinary shares that are readily tradable on an established securities market in the United States. The ordinary shares will be treated as readily tradable on an established securities market in the United States if they are listed on Nasdaq Global Select Market, which we intend them to be. However, if we are classified as a PFIC for the taxable year in which we pay a dividend or the prior taxable year, we will not be treated as a foreign qualified corporation and the preferential tax rate with respect to dividends paid to certain non-corporate U.S. Holders would not apply. U.S. Holders should consult their own tax advisors regarding the availability of the lower rate for dividends paid with respect to the ordinary shares.

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Subject to applicable limitations, some of which vary depending upon the U.S. Holder's circumstances, Irish income taxes withheld from dividends on ordinary shares may be creditable against the U.S. Holder's U.S. federal income tax liability. The rules governing foreign tax credits are complex, and U.S. Holders should consult their tax advisers regarding the creditability of foreign taxes in their particular circumstances. In lieu of claiming a foreign tax credit, U.S. Holders may, at their election, deduct foreign taxes, including the Irish tax, in computing their taxable income, subject to generally applicable limitations under U.S. law. An election to deduct foreign taxes instead of claiming foreign tax credits applies to all foreign taxes paid or accrued in the taxable year.

U.S. Holders should consult their tax advisers concerning the tax impact of the receipt of distributions from us.

Sale or Other Disposition of Ordinary Shares

Subject to the PFIC rules described above, for U.S. federal income tax purposes, gain or loss realized on the sale or other disposition of ordinary shares will be capital gain or loss, and will be long-term capital gain or loss if, on the date of the sale or other disposition, the U.S. Holder held the ordinary shares for more than one year. The amount of the gain or loss will equal the difference between the amount realized by the U.S. Holder on the disposition (i.e., the amount of cash plus the fair market value of any other property received) and the U.S. Holder's tax basis in the ordinary shares disposed of in each case as determined in U.S. dollars. This gain or loss will generally be U.S.-source gain or loss for foreign tax credit purposes. Non-corporate U.S. Holders (including individuals) generally will be subject to U.S. federal income tax on long-term capital gains at preferential rates. The deductibility of capital losses is subject to limitations.

Net Investment Income Tax

U.S. Holders that are individuals or estates or trusts that do not fall into a special class of trusts that is exempt from such tax, will be required to pay an additional 3.8% tax on the lesser of (1) the U.S. Holder's "net investment income" for the relevant taxable year and (2) the excess of the U.S. Holder's modified adjusted gross income for the taxable year over a certain threshold (which in the case of individuals will be between US $125,000 and US $250,000, depending on the individual's circumstances). A U.S. Holder's "net investment income" will generally include, among other things, dividends and capital gains. Such tax will apply to dividends and to capital gains from the sale or other disposition of the ordinary shares, unless derived in the ordinary course of the conduct of a trade or business (other than a trade or business that consists of certain passive or trading activities). Special rules apply and certain elections are available for certain U.S. Holders that are subject to the 3.8% tax on net investment income and hold shares in a PFIC. Potential investors should consult with their own tax advisers regarding the application of the net investment income tax to them as a result of their investment in our ordinary shares.

Information Reporting and Backup Withholding

Payments of dividends and sales proceeds that are made within the United States or through certain U.S.-related financial intermediaries generally are subject to information reporting, and may be subject to backup withholding, unless (1) the U.S. Holder is a corporation or other exempt recipient or (2) in the case of backup withholding, the U.S. Holder provides a correct taxpayer identification number and certifies that it is not subject to backup withholding.

Backup withholding is not an additional tax. Amounts withheld as backup withholding may be credited against such holder's U.S. federal income tax liability, and such holder may obtain a refund of any excess amounts withheld under the backup withholding rules by filing an appropriate claim for refund with the IRS and furnishing any required information in a timely manner. U.S. Holders of ordinary shares should consult their tax advisers regarding the application of the U.S. information reporting and backup withholding rules.

Information With Respect to Foreign Financial Assets

Certain U.S. Holders who are individuals (and, under proposed regulations, certain entities) may be required to report information relating to an interest in our ordinary shares on IRS Form 8938 (Statement of Specified Foreign Financial Assets), subject to certain exceptions (including an exception for ordinary shares held in accounts maintained by certain U.S. financial institutions). U.S. Holders should consult their tax advisers regarding the effect, if any, of this requirement on their ownership and disposition of the ordinary shares.

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UNDERWRITING

Subject to the terms and conditions set forth in the underwriting agreement, among us and Jefferies LLC and Stifel, Nicolaus & Company, Incorporated, as the representatives of the underwriters named below and the joint book-running managers of this offering, we have agreed to sell to the underwriters, and each of the underwriters has agreed, severally and not jointly, to purchase from us, the respective number of ordinary shares shown opposite its name below:

The underwriting agreement provides that the obligations of the several underwriters are subject to certain conditions precedent such as the receipt by the underwriters of officers' certificates and legal opinions and approval of certain legal matters by their counsel. The underwriting agreement provides that the underwriters will purchase all of the ordinary shares if any of them are purchased. If an underwriter defaults, the underwriting agreement provides that the purchase commitments of the nondefaulting underwriters may be increased or the underwriting agreement may be terminated. We have agreed to indemnify the underwriters and certain of their controlling persons against certain liabilities, including liabilities under the Securities Act, and to contribute to payments that the underwriters may be required to make in respect of those liabilities.

The underwriters have advised us that, following the completion of this offering, they currently intend to make a market in the ordinary shares as permitted by applicable laws and regulations. However, the underwriters are not obligated to do so, and the underwriters may discontinue any market-making activities at any time without notice in their sole discretion. Accordingly, no assurance can be given as to the liquidity of the trading market for the ordinary shares, that you will be able to sell any of the ordinary shares held by you at a particular time or that the prices that you receive when you sell will be favorable.

The underwriters are offering the ordinary shares subject to their acceptance of the ordinary shares from us and subject to prior sale. The underwriters reserve the right to withdraw, cancel or modify offers to the public and to reject orders in whole or in part.

Commission and Expenses

The underwriters have advised us that they propose to offer the ordinary shares to the public at the public offering price set forth on the cover page of this prospectus and to certain dealers, which may include the underwriters, at that price less a concession not in excess of $0.081 per ordinary share. After the offering, the public offering price, concession and reallowance to dealers may be reduced by the representatives. No such reduction will change the amount of proceeds to be received by us as set forth on the cover page of this prospectus.

The following table shows the public offering price, the underwriting discounts and commissions that we are to pay the underwriters and the proceeds, before expenses, to us in connection with this offering. Such

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amounts are shown assuming both no exercise and full exercise of the underwriters' option to purchase additional ordinary shares.

We have also agreed to pay MTS Health Partners, LP, or MTS, a fee of $250,000 for financial advisory services provided to us in respect of this offering. MTS is not acting as an underwriter in this offering.

We estimate expenses payable by us in connection with this offering, other than the underwriting discounts and commissions referred to above, will be approximately $385,000 (including the fee to MTS described above).

Listing

Our ordinary shares is listed on the Nasdaq Global Select Market under the trading symbol "SBBP".

Option to Purchase Additional Shares

We have granted to the underwriters an option, exercisable for 30 days from the date of this prospectus, to purchase, from time to time, in whole or in part, up to an aggregate of 1,666,666 ordinary shares from us at the public offering price set forth on the cover page of this prospectus, less underwriting discounts and commissions. If the underwriters exercise this option, each underwriter will be obligated, subject to specified conditions, to purchase a number of additional ordinary shares proportionate to that underwriter's initial purchase commitment as indicated in the table above.

No Sales of Similar Securities

We and our officers and directors have agreed, subject to specified exceptions, not to directly or indirectly:

§

sell, offer, contract or grant any option to sell (including any short sale), pledge, transfer, establish an open "put equivalent position" within the meaning of Rule 16a-l(h) under the Securities Exchange Act of 1934, as amended,



§

otherwise dispose of any ordinary shares, options or warrants to acquire ordinary shares or securities exchangeable or exercisable for or convertible into ordinary shares currently or hereafter owned either of record or beneficially, or



§

publicly announce an intention to do any of the foregoing for a period of 90 days after the date of this prospectus without the prior written consent of Jefferies LLC and Stifel, Nicolaus & Company, Incorporated.

This restriction terminates after the close of trading of the ordinary shares on and including the 90^th day after the date of this prospectus supplement.

Jefferies LLC and Stifel, Nicolaus & Company, Incorporated may, in their sole discretion and at any time or from time to time before the termination of the 90-day period release all or any portion of the securities subject to lock-up agreements. There are no existing agreements between the underwriters and any of our

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officers and directors who will execute a lock-up agreement, providing consent to the sale of ordinary shares prior to the expiration of the lock-up period.

Stabilization

The underwriters have advised us that they may engage in short sale transactions, stabilizing transactions, syndicate covering transactions or the imposition of penalty bids in connection with this offering. These activities may have the effect of stabilizing or maintaining the market price of the ordinary shares at a level above that which might otherwise prevail in the open market. Establishing short sales positions may involve either "covered" short sales or "naked" short sales.

"Covered" short sales are sales made in an amount not greater than the underwriters' option to purchase additional shares of our ordinary shares in this offering. The underwriters may close out any covered short position by either exercising their option to purchase additional ordinary shares in the open market. In determining the source of ordinary shares to close out the covered short position, the underwriters will consider, among other things, the price of ordinary shares available for purchase in the open market as compared to the price at which they may purchase ordinary shares through the option to purchase additional ordinary shares.

"Naked" short sales are sales in excess of the option to purchase additional ordinary shares. The underwriters must close out any naked short position by purchasing ordinary shares in the open market. A naked short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of our ordinary shares in the open market after pricing that could adversely affect investors who purchase in this offering.

A stabilizing bid is a bid for the purchase of ordinary shares on behalf of the underwriters for the purpose of fixing or maintaining the price of the ordinary shares. A syndicate covering transaction is the bid for or the purchase of ordinary shares on behalf of the underwriters to reduce a short position incurred by the underwriters in connection with the offering. Similar to other purchase transactions, the underwriter's purchases to cover the syndicate short sales may have the effect of raising or maintaining the market price of our ordinary shares or preventing or retarding a decline in the market price of our ordinary shares. As a result, the price of our ordinary shares may be higher than the price that might otherwise exist in the open market. A penalty bid is an arrangement permitting the underwriters to reclaim the selling concession otherwise accruing to a syndicate member in connection with the offering if the ordinary shares originally sold by such syndicate member are purchased in a syndicate covering transaction and therefore have not been effectively placed by such syndicate member.

Neither nor any of the underwriters make any representation or prediction as to the direction or magnitude of any effect that the transactions described above may have on the price of our ordinary shares. The underwriters are not obligated to engage in these activities and, if commenced, any of the activities may be discontinued at any time.

The underwriters may also engage in passive market making transactions in our ordinary shares on the Nasdaq Global Select Market in accordance with Rule 103 of Regulation M during a period before the commencement of offers or sales of ordinary shares in this offering and extending through the completion of distribution. A passive market maker must display its bid at a price not in excess of the highest independent bid of that security. However, if all independent bids are lowered below the passive market maker's bid, that bid must then be lowered when specified purchase limits are exceeded.

Electronic Distribution

A prospectus in electronic format may be made available by e-mail or on the web sites or through online services maintained by one or more of the underwriters or their affiliates. In those cases, prospective investors may view offering terms online and may be allowed to place orders online. The underwriters may

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agree with us to allocate a specific number of ordinary shares for sale to online brokerage account holders. Any such allocation for online distributions will be made by the underwriters on the same basis as other allocations. Other than the prospectus in electronic format, the information on the underwriters' web sites and any information contained in any other web site maintained by any of the underwriters is not part of this prospectus, has not been approved and/or endorsed by us or the underwriters and should not be relied upon by investors.

Other Activities and Relationships

The underwriters and certain of their respective affiliates are full service financial institutions engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory, investment management, investment research, principal investment, hedging, financing and brokerage activities. The underwriters and certain of their respective affiliates have, from time to time, performed, and may in the future perform, various commercial and investment banking and financial advisory services for us and our affiliates, for which they received or will receive customary fees and expenses. We entered into an equity distribution agreement with JMP Securities LLC on April 28, 2017 for the sale of up to $40 million of our ordinary shares through JMP Securities LLC, acting as our sales agent. As of the date of this prospectus, we have sold approximately $14 million in ordinary shares pursuant to this agreement. Accordingly, JMP Securities LLC has received and may in the future receive customary fees and commissions for these transactions.

In the ordinary course of their various business activities, the underwriters and certain of their respective affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers, and such investment and securities activities may involve securities and/or instruments issued by us and our affiliates. If the underwriters or their respective affiliates have a lending relationship with us, they routinely hedge their credit exposure to us consistent with their customary risk management policies. The underwriters and their respective affiliates may hedge such exposure by entering into transactions which consist of either the purchase of credit default swaps or the creation of short positions in our securities or the securities of our affiliates, including potentially the ordinary shares offered hereby. Any such short positions could adversely affect future trading prices of the ordinary shares offered hereby. The underwriters and certain of their respective affiliates may also communicate independent investment recommendations, market color or trading ideas and/or publish or express independent research views in respect of such securities or instruments and may at any time hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

Disclaimers About Non-U.S. Jurisdictions

Australia

This prospectus is not a disclosure document for the purposes of Australia's Corporations Act 2001 (Cth) of Australia, or Corporations Act, has not been lodged with the Australian Securities & Investments Commission and is only directed to the categories of exempt persons set out below. Accordingly, if you receive this prospectus in Australia:

You confirm and warrant that you are either:

§

a "sophisticated investor" under section 708(8)(a) or (b) of the Corporations Act;



§

a "sophisticated investor" under section 708(8)(c) or (d) of the Corporations Act and that you have provided an accountant's certificate to the Company which complies with the requirements of section 708(8)(c)(i) or (ii) of the Corporations Act and related regulations before the offer has been made;



§

a person associated with the Company under Section 708(12) of the Corporations Act; or



§

a "professional investor" within the meaning of section 708(11)(a) or (b) of the Corporations Act.

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To the extent that you are unable to confirm or warrant that you are an exempt sophisticated investor, associated person or professional investor under the Corporations Act any offer made to you under this prospectus is void and incapable of acceptance.

You warrant and agree that you will not offer any of the securities issued to you pursuant to this prospectus supplement for resale in Australia within 12 months of those securities being issued unless any such resale offer is exempt from the requirement to issue a disclosure document under section 708 of the Corporations Act.

Canada

Resale Restrictions

The distribution of our ordinary shares in Canada is being made only in the provinces of Ontario, Quebec, Alberta and British Columbia on a private placement basis exempt from the requirement that we prepare and file a prospectus with the securities regulatory authorities in each province where trades of these securities are made. Any resale of the ordinary sharesin Canada must be made under applicable securities laws which may vary depending on the relevant jurisdiction, and which may require resales to be made under available statutory exemptions or under a discretionary exemption granted by the applicable Canadian securities regulatory authority. Purchasers are advised to seek legal advice prior to any resale of the securities.

Representations of Canadian Purchasers

By purchasing ordinary shares in Canada and accepting delivery of a purchase confirmation, a purchaser is representing to us and the dealer from whom the purchase confirmation is received that:

§

the purchaser is entitled under applicable provincial securities laws to purchase the ordinary shares without the benefit of a prospectus qualified under those securities laws as it is an "accredited investor" as defined under National Instrument 45-106 — Prospectus Exemptions,



§

the purchaser is a "permitted client" as defined in National Instrument 31-103 — Registration Requirements, Exemptions and Ongoing Registrant Obligations,



§

where required by law, the purchaser is purchasing as principal and not as agent, and



§

the purchaser has reviewed the text above under "— Resale Restrictions."

Conflicts of Interest

Canadian purchasers are hereby notified that the underwriters are relying on the exemption set out in section 3A.3 or 3A.4, if applicable, of National Instrument 33-105 — Underwriting Conflicts from having to provide certain conflict of interest disclosure in this document.

Statutory Rights of Action

Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if the prospectus (including any amendment thereto) such as this document contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser's province or territory. The purchaser of these securities in Canada should refer to any applicable provisions of the securities legislation of the purchaser's province or territory for particulars of these rights or consult with a legal advisor.

Enforcement of Legal Rights

All of our directors and officers as well as the experts named herein may be located outside of Canada and, as a result, it may not be possible for Canadian purchasers to effect service of process within Canada upon us or those persons. All or a substantial portion of our assets and the assets of those persons may be located outside of Canada and, as a result, it may not be possible to satisfy a judgment against us or those persons in Canada or to enforce a judgment obtained in Canadian courts against us or those persons outside of Canada.

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Taxation and Eligibility for Investment

Canadian purchasers of our ordinary shares should consult their own legal and tax advisors with respect to the tax consequences of an investment in the ordinary shares in their particular circumstances and about the eligibility of the ordinary shares for investment by the purchaser under relevant Canadian legislation.

European Economic Area and the United Kingdom

In relation to each member state of the European Economic Area and the United Kingdom, or each, a Relevant State, an offer to the public of any securities which are the subject of the offering contemplated by this prospectus supplement and the accompanying prospectus may not be made in that Relevant State except that an offer to the public in that Relevant State of any securities may be made at any time under the following exemptions under the Prospectus Regulation:

§

to any legal entity which is a "qualified investor" as defined in the Prospectus Regulation;



§

to fewer than 150 natural or legal persons (other than qualified investors as defined in the Prospectus Regulation), as permitted under the Prospectus Regulation, subject to obtaining the prior consent of the underwriters or the underwriters nominated by us for any such offer; or



§

in any other circumstances falling within Article 1(4) of the Prospectus Regulation,

provided that no such offer of securities shall require us or any of the underwriters to publish a prospectus pursuant to Article 3 of the Prospectus Regulation or supplement a prospectus pursuant to Article 23 of the Prospectus Regulation.

For the purposes of this provision, the expression "offer to the public" in relation to any securities in any Relevant State means the communication in any form and by any means of sufficient information on the terms of the offer and the securities to be offered so as to enable an investor to decide to purchase or subscribe the securities, and the expression "Prospectus Regulation" means Regulation (EU) 2017/1129.

Hong Kong

No securities have been offered or sold, and no securities may be offered or sold, in Hong Kong, by means of any document, other than to persons whose ordinary business is to buy or sell shares or debentures, whether as principal or agent; or to "professional investors" as defined in the Securities and Futures Ordinance (Cap. 571) of Hong Kong, or SFO, and any rules made under that Ordinance; or in other circumstances which do not result in the document being a "prospectus" as defined in the Companies Ordinance (Cap. 32) of Hong Kong, or CO, or which do not constitute an offer or invitation to the public for the purpose of the CO or the SFO. No document, invitation or advertisement relating to the securities has been issued or may be issued or may be in the possession of any person for the purpose of issue (in each case whether in Hong Kong or elsewhere), which is directed at, or the contents of which are likely to be accessed or read by, the public of Hong Kong (except if permitted under the securities laws of Hong Kong) other than with respect to securities which are or are intended to be disposed of only to persons outside Hong Kong or only to "professional investors" as defined in the SFO and any rules made under that Ordinance.

This prospectus has not been registered with the Registrar of Companies in Hong Kong. Accordingly, this prospectus may not be issued, circulated or distributed in Hong Kong, and the securities may not be offered for subscription to members of the public in Hong Kong. Each person acquiring the securities will be required, and is deemed by the acquisition of the securities, to confirm that he is aware of the restriction on offers of the securities described in this prospectus and the relevant offering documents and that he is not acquiring, and has not been offered any securities in circumstances that contravene any such restrictions.

Israel

This document does not constitute a prospectus under the Israeli Securities Law, 5728-1968, or the Securities Law, and has not been filed with or approved by the Israel Securities Authority. In Israel, this prospectus is being distributed only to, and is directed only at, and any offer of the ordinary sharesis

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directed only at, (i) a limited number of persons in accordance with the Israeli Securities Law and (ii) investors listed in the first addendum, or the Addendum, to the Israeli Securities Law, consisting primarily of joint investment in trust funds, provident funds, insurance companies, banks, portfolio managers, investment advisors, members of the Tel Aviv Stock Exchange, underwriters, venture capital funds, entities with equity in excess of NIS 50 million and "qualified individuals," each as defined in the Addendum (as it may be amended from time to time), collectively referred to as qualified investors (in each case, purchasing for their own account or, where permitted under the Addendum, for the accounts of their clients who are investors listed in the Addendum). Qualified investors are required to submit written confirmation that they fall within the scope of the Addendum, are aware of the meaning of same and agree to it.

Japan

The offering has not been and will not be registered under the Financial Instruments and Exchange Law of Japan (Law No. 25 of 1948 of Japan, as amended), or FIEL, and the Initial Purchaser will not offer or sell any securities, directly or indirectly, in Japan or to, or for the benefit of, any resident of Japan (which term as used herein means any person resident in Japan, including any corporation or other entity organized under the laws of Japan), or to others for re-offering or resale, directly or indirectly, in Japan or to, or for the benefit of, any resident of Japan, except pursuant to an exemption from the registration requirements of, and otherwise in compliance with, the FIEL and any other applicable laws, regulations and ministerial guidelines of Japan.

MiFID II Product Governance

Any distributor subject to MiFID II that is offering, selling or recommending the ordinary shares is responsible for undertaking its own target market assessment in respect of the ordinary shares and determining its own distribution channels for the purposes of the MiFID product governance rules under Commission Delegated Directive (EU) 2017/593, or the Delegated Directive. Neither we nor the underwriters make any representations or warranties as to a distributor's compliance with the Delegated Directive.

Singapore

This prospectus has not been and will not be lodged or registered as a prospectus with the Monetary Authority of Singapore. Accordingly, this prospectus and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the notes may not be circulated or distributed, nor may the notes be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than (i) to an institutional investor under Section 274 of the Securities and Futures Act, Chapter 289 of Singapore, or the SFA, (ii) to a relevant person pursuant to Section 275(1), or any person pursuant to Section 275(1A), and in accordance with the conditions specified in Section 275, of the SFA, or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA.

Where the notes are subscribed or purchased under Section 275 of the SFA by a relevant person which is:

§

a corporation (which is not an accredited investor (as defined in Section 4A of the SFA)) the sole business of which is to hold investments and the entire share capital of which is owned by one or more individuals, each of whom is an accredited investor; or



§

a trust (where the trustee is not an accredited investor) whose sole purpose is to hold investments and each beneficiary of the trust is an individual who is an accredited investor,



§

securities (as defined in Section 239(1) of the SFA) of that corporation or the beneficiaries' rights and interest (howsoever described) in that trust shall not be transferred within six months after that corporation or that trust has acquired the notes pursuant to an offer made under Section 275 of the SFA except:



§

to an institutional investor or to a relevant person defined in Section 275(2) of the SFA, or to any person arising from an offer referred to in Section 275(1A) or Section 276(4)(i)(B) of the SFA;

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§

where no consideration is or will be given for the transfer;



§

where the transfer is by operation of law;



§

as specified in Section 276(7) of the SFA; or



§

as specified in Regulation 32 of the Securities and Futures (Offers of Investments) (Shares and Debentures) Regulations 2005 of Singapore.

Switzerland

The securities may not be publicly offered in Switzerland and will not be listed on the SIX Swiss Exchange, or SIX, or on any other stock exchange or regulated trading facility in Switzerland. This prospectus has been prepared without regard to the disclosure standards for issuance prospectuses under art. 652a or art. 1156 of the Swiss Code of Obligations or the disclosure standards for listing prospectuses under art. 27 ff. of the SIX Listing Rules or the listing rules of any other stock exchange or regulated trading facility in Switzerland. Neither this prospectus nor any other offering or marketing material relating to the securities or the offering may be publicly distributed or otherwise made publicly available in Switzerland.

Neither this prospectus nor any other offering or marketing material relating to the offering, the Company or the securities have been or will be filed with or approved by any Swiss regulatory authority. In particular, this prospectus will not be filed with, and the offer of securities will not be supervised by, the Swiss Financial Market Supervisory Authority FINMA, and the offer of securities has not been and will not be authorized under the Swiss Federal Act on Collective Investment Schemes, or CISA. The investor protection afforded to acquirers of interests in collective investment schemes under the CISA does not extend to acquirers of securities.

Selling restrictions addressing additional United Kingdom securities laws

This prospectus is only being distributed to, and is only directed at, persons in the United Kingdom that are qualified investors within the meaning of the Prospectus Regulation that are also (i) investment professionals falling within Article 19(5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005, as amended, or the Order, and/or (ii) high net worth entities falling within Article 49(2)(a) to (d) of the Order and other persons to whom it may lawfully be communicated, each such person being referred to as a "relevant person".

This prospectus and its contents are confidential and should not be distributed, published or reproduced (in whole or in part) or disclosed by recipients to any other persons in the United Kingdom. Any person in the United Kingdom that is not a relevant person should not act or rely on this document or any of its contents.

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LEGAL MATTERS

The validity of the ordinary shares and certain other matters of Irish law will be passed upon for us by Arthur Cox, Dublin, Ireland. Certain matters of U.S. federal and New York State law will be passed upon for us by Reed Smith LLP, New York, New York. The underwriters are being represented by Cooley LLP, New York, New York.

EXPERTS

The consolidated financial statements of Strongbridge Biopharma plc at December 31, 2019 and 2018, and for each of the three years in the period ended December 31, 2019, incorporated by reference in this prospectus supplement, the accompanying prospectus and the related registration statement, have been audited by Ernst & Young LLP, independent registered public accounting firm, as set forth in its report thereon incorporated elsewhere herein by reference and are incorporated herein in reliance upon such report given on the authority of such firm as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

As required by the Securities Act, we have filed with the SEC a registration statement on Form S-3, of which this prospectus is a part, with respect to the securities offered hereby. This prospectus does not contain all of the information included in the registration statement. Statements in this prospectus concerning the provisions of any document are not necessarily complete. You should refer to the copies of the documents filed as exhibits to the registration statement or otherwise filed by us with the SEC for a more complete understanding of the matter involved. Each statement concerning these documents is qualified in its entirety by such reference.

We file annual, quarterly and current reports, proxy statements and other information with the SEC. We also make available, free of charge, on or through our Internet web site (www.strongbridgebio.com) our Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K, Proxy Statements on Schedule 14A and, if applicable, amendments to those reports filed or furnished pursuant to Section 13(a) of the Exchange Act, as soon as reasonably practicable after we electronically file such material with, or furnish it to, the SEC. Please note, however, that we have not incorporated any other information by reference from our Internet web site, other than the documents listed below under the heading "Incorporation of Information by Reference."

Also, the SEC maintains an Internet web site that contains reports, proxy and information statements, and other information regarding issuers, including us, that file electronically with the SEC. The public can obtain any documents that we file electronically with the SEC at http://www.sec.gov.

INCORPORATION OF INFORMATION BY REFERENCE

The SEC allows us to "incorporate by reference" in this prospectus supplement and the accompanying prospectus the information that we file with them. This means that we can disclose important information to you in this document by referring you to other filings we have made with the SEC. The information incorporated by reference is considered to be part of this prospectus supplement and the accompanying prospectus, and later information we file with the SEC will update and supersede this information. We incorporate by reference the documents listed below and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act. We are not incorporating by reference any

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documents or portions thereof, whether specifically listed below or filed in the future, that are not deemed "filed" with the SEC (including the Current Reports on Form 8-K listed below), unless otherwise specified.

§

Our Annual Report on Form 10-K for the fiscal year ended December 31, 2019, filed with the SEC on February 28, 2020;



§

Our Quarterly Reports on Form 10-Q for the fiscal quarters ended March 31, 2020 and June 30, 2020, filed with the SEC on May 6, 2020 and August 4, 2020, respectively;



§

Our Definitive Proxy Statement on Schedule 14A, filed with the SEC on April 1, 2020;



§

The Current Reports on Form 8-K filed with the SEC on May 14, 2020, May 20, 2020, July 7, 2020 and September 8, 2020; and



§

The description of our securities contained in our Registration Statement on Form 8-A (File No. 001-37569), filed with the SEC on September 25, 2015 pursuant to Section 12(b) of the Exchange Act, including any amendment or report filed for the purpose of updating such description.

Pursuant to Rule 412 under the Securities Act, any statement contained in the documents incorporated or deemed to be incorporated by reference in this prospectus supplement and the accompanying prospectus shall be deemed to be modified, superseded or replaced for purposes of this prospectus supplement and the accompanying prospectus to the extent that a statement contained herein or in any other subsequently filed document which also is incorporated or deemed to be incorporated by reference in this prospectus supplement and the accompanying prospectusmodifies, supersedes or replaces such statement. Any such statement so modified, superseded or replaced shall not be deemed, except as so modified, superseded or replaced, to constitute a part of this prospectus supplement or the accompanying prospectus. Investors should review these reports as they may disclose a change in our business, prospects, financial condition or other affairs after the date of this prospectus.

Upon your written or oral request, we will provide at no cost to you a copy of any and all of the information that is incorporated by reference in this prospectus. Requests for such documents should be directed to:

Stephen Long, Esq.
Chief Legal Officer
Strongbridge Biopharma plc
900 Northbrook Drive, Suite 200
Trevose, PA 19053

You may also access the documents incorporated by reference in this prospectus supplement and the accompanying prospectus through our website www.strongbridgebio.com. Except for the specific incorporated documents listed above, no information available on or through our website shall be deemed to be incorporated in this prospectus s supplement or the accompanying prospectus.

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PROSPECTUS

$91,174,535

ORDINARY SHARES
PREFERRED SHARES
DEBT SECURITIES
WARRANTS
RIGHTS
UNITS

        This prospectus will allow us to issue, from time to time at prices and on terms to be determined at or prior to the time of the offering, up to $91,174,535 of any combination of the securities described in this prospectus, either individually or in units, less the aggregate dollar amount of all securities previously sold hereunder. We may also offer ordinary shares or preferred shares upon conversion of or exchange for the debt securities; or ordinary shares, preferred shares or debt securities upon the exercise of warrants or rights.

        This prospectus describes the general terms of these securities and the general manner in which these securities will be offered. We will provide you with the specific terms of any offering in one or more supplements to this prospectus. The prospectus supplements will also describe the specific manner in which these securities will be offered and may also supplement, update or amend information contained in this document. You should read this prospectus and any prospectus supplement, as well as any documents incorporated by reference into this prospectus or any prospectus supplement, carefully before you invest.

        Our securities may be sold directly by us to you, through agents designated from time to time or to or through underwriters or dealers. For additional information on the methods of sale, you should refer to the section entitled "Plan of Distribution" in this prospectus and in the applicable prospectus supplement. If any underwriters or agents are involved in the sale of our securities with respect to which this prospectus is being delivered, the names of such underwriters or agents and any applicable fees, commissions or discounts and over-allotment options will be set forth in a prospectus supplement. The price to the public of such securities and the net proceeds that we expect to receive from such sale will also be set forth in a prospectus supplement.

        Our ordinary shares are listed on the Nasdaq Global Select Market, under the symbol "SBBP." On March 21, 2018, the last reported sale price of our ordinary shares on the Nasdaq Global Select Market was $8.20 per share.

        Investing in our securities involves a high degree of risk. Before deciding whether to invest in our securities, you should consider carefully the risks that we have described on page 4 of this prospectus under the caption "Risk Factors" and in the "Risk Factors" section of our periodic reports filed with the U.S. Securities and Exchange Commission. We may include specific risk factors in supplements to this prospectus under the caption "Risk Factors."

        We are an "emerging growth company" as defined by the Jumpstart Our Business Startups Act of 2012 and, as such, we have elected to comply with certain reduced public company reporting requirements for this prospectus supplement and future filings.

        Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is March 29, 2018

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ABOUT THIS PROSPECTUS

        This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission ("SEC"), utilizing a "shelf" registration process. Under this shelf registration process, we may offer ordinary shares, preferred shares, various series of debt securities and/or warrants, or rights to purchase any of such securities, either individually or in units, in one or more offerings, with a total value of up to $91,174,535. This prospectus provides you with a general description of the securities we may offer. Each time we offer a type or series of securities under this prospectus, we will provide a prospectus supplement that will contain specific information about the terms of that offering.

        The prospectus supplement may also add, update or change information contained or incorporated by reference in this prospectus. However, no prospectus supplement will offer a security that is not registered and described in this prospectus at the time of its effectiveness. This prospectus, together with the applicable prospectus supplements and the documents incorporated by reference into this prospectus, includes all material information relating to the offering of securities under this prospectus. You should carefully read this prospectus, the applicable prospectus supplement, the information and documents incorporated herein by reference and the additional information under the headings "Where You Can Find More Information" and "Incorporation of Information By Reference" before making an investment decision.

        You should rely only on the information we have provided or incorporated by reference in this prospectus or any prospectus supplement. We have not authorized anyone to provide you with information different from that contained or incorporated by reference in this prospectus. No dealer, salesperson or other person is authorized to give any information or to represent anything not contained or incorporated by reference in this prospectus. You must not rely on any unauthorized information or representation. This prospectus is an offer to sell only the securities offered hereby, but only under circumstances and in jurisdictions where it is lawful to do so. You should assume that the information in this prospectus or any prospectus supplement is accurate only as of the date on the front of the document and that any information we have incorporated herein by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus or any sale of a security.

        We further note that the representations, warranties and covenants made by us in any agreement that is filed as an exhibit to any document that is incorporated by reference in the accompanying prospectus were made solely for the benefit of the parties to such agreement, including, in some cases, for the purpose of allocating risk among the parties to such agreements, and should not be deemed to be a representation, warranty or covenant to you. Moreover, such representations, warranties or covenants were accurate only as of the date when made. Accordingly, such representations, warranties and covenants should not be relied on as accurately representing the current state of our affairs.

        This prospectus may not be used to consummate sales of our securities, unless it is accompanied by a prospectus supplement. To the extent there are inconsistencies between any prospectus supplement, this prospectus and any documents incorporated by reference, the document with the most recent date will control.

        Other than in the United States, no action has been taken by us or any underwriters that would permit a public offering of the securities offered by this prospectus in any jurisdiction where action for that purpose is required. The securities offered by this prospectus may not be offered or sold, directly or indirectly, nor may this prospectus or any other offering material or advertisements in connection with the offer and sale of any such securities be distributed or published in any jurisdiction, except under circumstances that will result in compliance with the applicable rules and regulations of that jurisdiction. Persons into whose possession this prospectus comes are advised to inform themselves about and to observe any restrictions relating to the offering and the distribution of this prospectus. This prospectus does not constitute an offer to sell or a solicitation of an offer to buy any securities offered by this prospectus in any jurisdiction in which such an offer or a solicitation is unlawful.

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CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

        Some of the statements in this prospectus and in any prospectus supplement we may file constitute "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21E of the Securities Exchange Act of 1934 as amended, or the Exchange Act. These statements relate to future events concerning our business and to our future revenues, operating results and financial condition. In some cases, you can identify forward-looking statements by terminology such as "may," "will," "could," "would," "should," "expect," "plan," "anticipate," "intend," "believe," "estimate," "forecast," "predict," "propose," "potential" or "continue," or the negative of those terms or other comparable terminology.

        Any forward looking statements contained in this prospectus or any prospectus supplement are only estimates or predictions of future events based on information currently available to our management and management's current beliefs about the potential outcome of future events. Whether these future events will occur as management anticipates, whether we will achieve our business objectives, and whether our revenues, operating results or financial condition will improve in future periods are subject to numerous risks. There are a number of important factors that could cause actual results to differ materially from the results anticipated by these forward-looking statements. These important factors include those that we discuss under the heading "Risk Factors" and in other sections of our Annual Report on Form 10-K for the year ended December 31, 2017, as well as in our other reports filed on from time to time with the SEC, that are incorporated by reference into this prospectus. You should read these factors and the other cautionary statements made in this prospectus and in the documents we incorporate by reference into this prospectus as being applicable to all related forward-looking statements wherever they appear in this prospectus or the documents we incorporate by reference into this prospectus. If one or more of these factors materialize, or if any underlying assumptions prove incorrect, our actual results, performance or achievements may vary materially from any future results, performance or achievements expressed or implied by these forward-looking statements. We undertake no obligation to publicly update any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law.

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RISK FACTORS

        Investing in our securities involves significant risks. You should review carefully the risks and uncertainties described under the heading "Risk Factors" contained in, or incorporated into, the applicable prospectus supplement and any related free writing prospectus, and under similar headings in the other documents that are incorporated by reference herein or therein. Each of the referenced risks and uncertainties could adversely affect our business, operating results and financial condition, as well as adversely affect the value of an investment in our securities. Additional risks not known to us or that we believe are immaterial may also adversely affect our business, operating results and financial condition and the value of an investment in our securities.

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CONSOLIDATED RATIO OF EARNINGS TO FIXED CHARGES AND EARNINGS TO COMBINED FIXED CHARGES AND PREFERENCE DIVIDENDS

        The following table sets forth our ratio of earnings to fixed charges for each of the periods indicated. You should read this table in conjunction with the consolidated financial statements and notes incorporated by reference in this prospectus.

        The ratio of earnings to combined fixed charges and preference dividends for the periods presented is the same as the ratio of earnings to fixed charges since we have no outstanding preferred shares and, therefore, no dividend requirements.

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USE OF PROCEEDS

        We cannot assure you that we will receive any proceeds in connection with securities which may be offered pursuant to this prospectus. Unless otherwise indicated in the applicable prospectus supplement, we intend to use any net proceeds from the sale of securities under this prospectus for our operations and for other general corporate purposes, including, but not limited to, our internal research and development programs and the development of new programs, general working capital and possible future acquisitions. We have not determined the amounts we plan to spend on any of the areas listed above or the timing of these expenditures. As a result, our management will have broad discretion to allocate the net proceeds, if any, we receive in connection with securities offered pursuant to this prospectus for any purpose. Pending application of the net proceeds as described above, we may initially invest the net proceeds in short-term, investment-grade, interest-bearing securities or apply them to the reduction of short-term indebtedness.

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PLAN OF DISTRIBUTION

General Plan of Distribution

        We may offer securities under this prospectus from time to time pursuant to underwritten public offerings, negotiated transactions, block trades or a combination of these methods. We may sell the securities (1) through underwriters or dealers, (2) through agents or (3) directly to one or more purchasers, or through a combination of such methods. We may distribute the securities from time to time in one or more transactions at:

•

a fixed price or prices, which may be changed from time to time;



•

market prices prevailing at the time of sale;



•

prices related to the prevailing market prices; or



•

negotiated prices.

        We may directly solicit offers to purchase the securities being offered by this prospectus. We may also designate agents to solicit offers to purchase the securities from time to time. We will name in a prospectus supplement any underwriter or agent involved in the offer or sale of the securities.

        If we utilize a dealer in the sale of the securities being offered by this prospectus, we will sell the securities to the dealer, as principal. The dealer may then resell the securities to the public at varying prices to be determined by the dealer at the time of resale.

        If we utilize an underwriter in the sale of the securities being offered by this prospectus, we will execute an underwriting agreement with the underwriter at the time of sale, and we will provide the name of any underwriter in the prospectus supplement which the underwriter will use to make re-sales of the securities to the public. In connection with the sale of the securities, we, or the purchasers of the securities for whom the underwriter may act as agent, may compensate the underwriter in the form of underwriting discounts or commissions. The underwriter may sell the securities to or through dealers, and the underwriter may compensate those dealers in the form of discounts, concessions or commissions.

        With respect to underwritten public offerings, negotiated transactions and block trades, we will provide in the applicable prospectus supplement information regarding any compensation we pay to underwriters, dealers or agents in connection with the offering of the securities, and any discounts, concessions or commissions allowed by underwriters to participating dealers. Underwriters, dealers and agents participating in the distribution of the securities may be deemed to be underwriters within the meaning of the Securities Act of 1933, as amended, or the Securities Act, and any discounts and commissions received by them and any profit realized by them on resale of the securities may be deemed to be underwriting discounts and commissions. We may enter into agreements to indemnify underwriters, dealers and agents against civil liabilities, including liabilities under the Securities Act, or to contribute to payments they may be required to make in respect thereof.

        If so indicated in the applicable prospectus supplement, we will authorize underwriters or other persons acting as our agents to solicit offers by certain institutions to purchase securities from us pursuant to delayed delivery contracts providing for payment and delivery on the date stated in the prospectus supplement. Each contract will be for an amount not less than, and the aggregate amount of securities sold pursuant to such contracts shall not be less nor more than, the respective amounts stated in the prospectus supplement. Institutions with whom the contracts, when authorized, may be made include commercial and savings banks, insurance companies, pension funds, investment companies,

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educational and charitable institutions and other institutions, but shall in all cases be subject to our approval. Delayed delivery contracts will not be subject to any conditions except that:

•

the purchase by an institution of the securities covered under that contract shall not at the time of delivery be prohibited under the laws of the jurisdiction to which that institution is subject; and



•

if the securities are also being sold to underwriters acting as principals for their own account, the underwriters shall have purchased such securities not sold for delayed delivery. The underwriters and other persons acting as our agents will not have any responsibility in respect of the validity or performance of delayed delivery contracts.

        Ordinary shares sold pursuant to the registration statement of which this prospectus is a part will be authorized for quotation and trading on the Nasdaq Global Select Market. The applicable prospectus supplement will contain information, where applicable, as to any other listing, if any, on the Nasdaq Global Select Market or any securities market or other securities exchange of the securities covered by the prospectus supplement. We can make no assurance as to the liquidity of or the existence of trading markets for any of the securities.

        In order to facilitate the offering of the securities, certain persons participating in the offering may engage in transactions that stabilize, maintain or otherwise affect the price of the securities. This may include over-allotments or short sales of the securities, which involve the sale by persons participating in the offering of more securities than we sold to them. In these circumstances, these persons would cover such over-allotments or short positions by making purchases in the open market or by exercising their over-allotment option. In addition, these persons may stabilize or maintain the price of the securities by bidding for or purchasing the applicable security in the open market or by imposing penalty bids, whereby selling concessions allowed to dealers participating in the offering may be reclaimed if the securities sold by them are repurchased in connection with stabilization transactions. The effect of these transactions may be to stabilize or maintain the market price of the securities at a level above that which might otherwise prevail in the open market. These transactions may be discontinued at any time.

        The underwriters, dealers and agents may engage in other transactions with us, or perform other services for us, in the ordinary course of their business.

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DESCRIPTION OF SHARE CAPITAL

General

        Our authorized share capital consists of €40,000, divided into 40,000 deferred ordinary shares with a nominal value of €1.00 per share, and $7,000,000, divided into 600,000,000 ordinary shares with a nominal value of $0.01 per share and 100,000,000 preferred shares with a nominal value of $0.01 per share.

        We may issue shares subject to the maximum authorized share capital contained in our Memorandum of Association. The authorized share capital may be increased or reduced by a resolution approved by a simple majority of the votes cast at a general meeting of our shareholders, referred to under Irish law as an "ordinary resolution." Our authorized share capital may be divided into shares of such nominal value as the resolution shall prescribe. As a matter of Irish law, the directors of a company may issue new ordinary or preferred shares without shareholder approval once authorized to do so by the memorandum and articles of association or by an ordinary resolution adopted by our shareholders at a general meeting. The authorization may be granted for a maximum period of five years, at which point it must be renewed by shareholders by an ordinary resolution. Accordingly, our Articles of Association, or Articles, authorize our board of directors to issue new ordinary or preferred shares without shareholder approval for a period of five years from the date of the adoption of our Articles on September 9, 2015. The authority to issue preferred shares provides us with the flexibility to consider and respond to future business needs and opportunities as they arise from time to time, including in connection with capital raising, financing and acquisition transactions or opportunities.

        We may, by ordinary resolution, reduce our authorized share capital in any way. We also may, by special resolution and subject to confirmation by the Irish High Court, reduce or cancel our issued share capital in any manner permitted by the Irish Companies Act.

        As of March 21, 2018, we had 40,000 deferred ordinary shares outstanding, 45,531,827 ordinary shares outstanding and zero preferred shares outstanding. As of March 21, 2018, we also had outstanding options to acquire 8,006,527 ordinary shares of our share capital, having a weighted-average exercise price of $7.33 per share, warrants to purchase an aggregate of 8,803,253 ordinary shares, and 173,400 ordinary shares issuable upon the vesting of restricted stock units.

        The following description of our share capital and certain provisions of our Articles are summaries and are qualified by reference to our Articles.

Deferred Shares

        The authorized and issued share capital includes 40,000 deferred ordinary shares, which are required in order to satisfy statutory minimum capital requirements of an Irish public limited company. The holders of the deferred ordinary shares are not entitled to receive any dividend or distribution, to attend, speak or vote at any general meeting, and have no effective rights to participate in the assets of our Company. The holders of our deferred ordinary shares are not entitled to a vote.

Ordinary Shares

        Under our Articles, each holder of our ordinary shares is entitled to one vote for each ordinary share that he or she holds. Our ordinary shares do not have sinking fund provisions.

Preferred Shares

        Under our Articles, our board of directors is authorized to issue preferred shares on a non-pre-emptive basis, with discretion as to the terms attaching to the preferred shares, including as to voting, dividend and conversion rights and priority relative to other classes of shares with respect to

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dividends and upon a liquidation. As noted above, this authority extends until five years from the date of the adoption of our Articles on September 9, 2015, at which time it will expire unless renewed by our shareholders.

        Notwithstanding this authority, under the Irish Takeover Rules our board of directors would not be permitted to issue any of our shares, including preferred shares, during a period when an offer has been made for us or is believed to be imminent unless the issue is (i) approved by our shareholders at a general meeting; (ii) consented to by the Irish Takeover Panel on the basis it would not constitute action frustrating the offer; (iii) consented to by the Irish Takeover Panel and approved by the holders of more than 50% of our shares carrying voting rights; (iv) consented to by the Irish Takeover Panel in circumstances where a contract for the issue of the shares had been entered into prior to that period; or (v) consented to by the Irish Takeover Panel in circumstances where the issue of the shares was decided by our directors prior to that period and either action has been taken to implement the issuance (whether in part or in full) prior to such period or the issuance was otherwise in the ordinary course of business.

        While we do not have any current specific plans, arrangements or understandings, written or oral, to issue any preferred shares for any purpose, we are continually evaluating our financial position and analyzing the possible benefits of issuing additional debt securities, equity securities, convertible securities or a combination thereof in connection with, among other things: (i) repaying indebtedness; (ii) financing acquisitions; or (iii) strengthening our balance sheet. The availability of preferred shares gives us flexibility to respond to future capital raising, financing and acquisition needs and opportunities without the delay and expense associated with holding an extraordinary general meeting of our shareholders to obtain further shareholder approval.

Preemption Rights

        Under Irish law, unless otherwise authorized, when an Irish public limited company issues shares for cash to new shareholders, it is required first to offer those shares on the same or more favorable terms to existing shareholders of the company on a pro rata basis, commonly referred to as the statutory preemption right. However, we have opted out of these preemption rights in our Articles as permitted under Irish law. Because Irish law requires this opt-out to be renewed every five years by a special resolution of the shareholders, our Articles provide that this opt-out will lapse five years after the adoption of our current Articles on September 9, 2015. A special resolution requires not less than 75% of the votes of our shareholders cast at a general meeting. If the opt-out is not renewed, shares issued for cash must be offered to pre-existing shareholders of Strongbridge pro rata to their existing shareholding before the shares can be issued to any new shareholders. The statutory preemption rights do not apply where shares are issued for non-cash consideration and do not apply to the issue of non-equity shares (that is, shares that have the right to participate only up to a specified amount in any income or capital distribution).

Dividends

        Under Irish law, dividends and distributions may only be made from distributable reserves. Distributable reserves generally means accumulated realized profits less accumulated realized losses and includes reserves created by way of capital reduction. In addition, no distribution or dividend may be made unless our net assets are equal to, or in excess of, the aggregate of our called up share capital plus undistributable reserves and the distribution does not reduce our net assets below such aggregate. Undistributable reserves include undenominated capital and the amount by which our accumulated unrealized profits, so far as not previously utilized by any capitalization, exceed our accumulated unrealized losses, so far as not previously written off in a reduction of capital approved by the Irish High Court without restriction, or a reorganization of capital.

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        The determination as to whether or not we have sufficient distributable reserves to fund a dividend must be made by reference to our "relevant financial statements." The "relevant financial statements" will be either the last set of unconsolidated annual audited financial statements or other financial statements properly prepared in accordance with the Irish Companies Act, which give a "true and fair view" of our unconsolidated financial position and accord with accepted accounting practice.

        The mechanism as to who declares a dividend and when a dividend shall become payable is governed by our Articles. Our Articles authorize our board of directors to declare dividends without shareholder approval to the extent they appear justified by profits lawfully available for distribution. Our board of directors may also recommend a dividend to be approved and declared by the shareholders at a general meeting. Our board of directors may direct that the payment be made by distribution of assets, shares or cash, and no dividend issued may exceed the amount recommended by our board of directors. Dividends may be declared and paid in the form of cash or non-cash assets and may be paid in dollars or any other currency.

        Our board of directors may deduct from any dividend payable to any shareholder any amounts payable by such shareholder to us in relation to our ordinary shares.

        Our board of directors may also authorize us to issue shares with preferred rights to participate in dividends we declare. The holders of preferred shares may, depending on their terms, rank senior to the ordinary shares in terms of dividend rights or be entitled to claim arrears of a declared dividend out of subsequently declared dividends in priority to ordinary shareholders.

Bonus Shares

        Under our Articles, our board of directors may resolve to capitalize any amount credited to any reserve, including our undenominated capital, or credited to the profit and loss account, and use such amount for the issuance to shareholders of shares as fully paid bonus shares on the same basis of entitlement as would apply in respect of a dividend distribution.

Share Repurchases and Redemptions

Overview

        Our Articles provide that any ordinary share that we have agreed to acquire shall be deemed to be a redeemable share. Accordingly, for Irish law purposes, the repurchase of ordinary shares by us may technically be effected as a redemption of those shares as described under "—Repurchases and Redemptions." If our Articles did not contain such provision, repurchases by us would be subject to many of the same rules that apply to purchases of ordinary shares by subsidiaries described under "—Purchases by Subsidiaries," including the shareholder approval requirements described below, and the requirement that any purchases on market be effected on a "recognized stock exchange," which, for purposes of the Irish Companies Act, includes Nasdaq.

Repurchases and Redemptions

        Under Irish law, subject to the conditions summarized below, a company may issue redeemable shares and may only redeem them out of distributable reserves or the proceeds of a new issue of ordinary shares for that purpose. We do not expect to have any distributable reserves for the foreseeable future. We may only issue redeemable shares if the nominal value of the issued share capital that is not redeemable is not less than 10% of the nominal value of our total issued share capital. All redeemable shares must also be fully paid and the terms of redemption of the shares must provide for payment on redemption. Redeemable shares may, upon redemption, be cancelled or held in treasury. Based on the provision of our Articles described above, shareholder approval will not be required to redeem our ordinary shares.

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        We may also be given an additional general authority to purchase our own shares on market, which would take effect on the same terms and be subject to the same conditions as applicable to purchases by our subsidiaries as described below.

        Our board of directors may also issue preferred shares, which may be redeemed at the option of either us or the shareholder, depending on the terms of such preferred shares. Please see "—Authorized Share Capital" above for additional information on preferred shares.

        Repurchased and redeemed shares may be cancelled or held as treasury shares. The nominal value of treasury shares held by us at any time must not exceed 10% of the nominal value of our issued share capital. We may not exercise any voting rights in respect of any shares held as treasury shares. Treasury shares may be cancelled by us or re-issued subject to certain conditions.

Purchases by Subsidiaries

        Under Irish law, an Irish or non-Irish subsidiary may purchase our ordinary shares either on market or off market. For one of our subsidiaries to make purchases on market of our ordinary shares, the shareholders must provide general authorization for such purchase by way of ordinary resolution. However, as long as this general authority has been granted, no specific shareholder authority for a particular on market purchase by a subsidiary of our ordinary shares is required. For a purchase by a subsidiary off market, the proposed purchase contract must be authorized by special resolution of our shareholders before the contract is entered into. The person whose ordinary shares are to be bought back cannot vote in favor of the special resolution and the purchase contract must be on display or must be available for inspection by our shareholders at our registered office from the date of the notice of the meeting at which the resolution approving the contract is to be proposed.

        In order for one of our subsidiaries to make an on market purchase of our ordinary shares, such shares must be purchased on a "recognized stock exchange." Nasdaq is specified as a recognized stock exchange for this purpose by Irish law.

        The number of ordinary shares held by our subsidiaries at any time will count as treasury shares and will be included in any calculation of the permitted treasury share threshold of 10% of the nominal value of our issued share capital. While a subsidiary holds any of our shares, it cannot exercise any voting rights in respect of those shares. The acquisition of our ordinary shares by a subsidiary must be funded out of distributable reserves of the subsidiary.

Lien on Shares, Calls on Shares and Forfeiture of Shares

        Our Articles provide that we will have a first and paramount lien on every share that is not a fully paid share for all amounts payable at a fixed time or called in respect of that share. Subject to the terms of their allotment, directors may call for any unpaid amounts in respect of any shares to be paid, and if payment is not made, the shares may be forfeited. These provisions are customary in the articles of association of an Irish public company limited by shares such as our company and will only be applicable to shares that have not been fully paid.

Anti-Takeover Provisions

Business Combinations with Interested Shareholders

        Our Articles include a provision similar to Section 203 of the Delaware General Corporation Law, which generally prohibits us from engaging in a business combination with an interested shareholder for

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a period of three years following the date the person became an interested shareholder, unless, in general:

•

our board of directors approved the transaction which resulted in the shareholder becoming an interested shareholder;



•

upon consummation of the transaction which resulted in the shareholder becoming an interested shareholder, the shareholder owned at least 85% of the voting shares outstanding at the time of commencement of such transaction, excluding for purposes of determining the number of voting shares outstanding (but not the outstanding voting shares owned by the interested shareholder), voting shares owned by persons who are directors and also officers and by certain employee share plans; or



•

the business combination is approved by our board of directors and authorized at an annual or extraordinary general meeting of shareholders by the affirmative vote of the holders of at least 75% of the outstanding voting shares that are not owned by the interested shareholder.

        A "business combination" is generally defined as a merger, asset or stock sale or other transaction resulting in a financial benefit to the interested shareholder. An "interested shareholder" is generally defined as a person who, together with affiliates and associates, owns or, within three years prior to the date in question, owned 15% or more of our outstanding voting shares.

Irish Takeover Rules and Substantial Acquisition Rules

        A transaction in which a third party seeks to acquire 30% or more of our voting rights and any other acquisitions of our securities will be governed by the Irish Takeover Panel Act 1997 and the Irish Takeover Rules made thereunder, or the Irish Takeover Rules, and will be regulated by the Irish Takeover Panel. The "General Principles" of the Irish Takeover Rules and certain important aspects of the Irish Takeover Rules are described below.

General Principles

        The Irish Takeover Rules are built on the following General Principles which will apply to any transaction regulated by the Irish Takeover Panel:

•

in the event of an offer, all holders of securities of the target company must be afforded equivalent treatment and, if a person acquires control of a company, the other holders of securities must be protected;



•

the holders of securities in the target company must have sufficient time and information to enable them to reach a properly informed decision on the offer; where it advises the holders of securities, the board of directors of the target company must give its views on the effects of the implementation of the offer on employment, employment conditions and the locations of the target company's place of business;



•

a target company's board of directors must act in the interests of that company as a whole and must not deny the holders of securities the opportunity to decide on the merits of the offer;



•

false markets must not be created in the securities of the target company, the bidder or any other company concerned by the offer in such a way that the rise or fall of the prices of the securities becomes artificial and the normal functioning of the markets is distorted;



•

a bidder can only announce an offer after ensuring that he or she can fulfill in full the consideration offered, if such is offered, and after taking all reasonable measures to secure the implementation of any other type of consideration;

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a target company may not be hindered in the conduct of its affairs longer than is reasonable by an offer for its securities; and



•

a "substantial acquisition" of securities, whether such acquisition is to be effected by one transaction or a series of transactions, shall take place only at an acceptable speed and shall be subject to adequate and timely disclosure.

Mandatory Bid

        Under certain circumstances, a person who acquires shares, or other voting securities, of a company may be required under the Irish Takeover Rules to make a mandatory cash offer for the remaining outstanding voting securities in that company at a price not less than the highest price paid for the securities by the acquiror, or any parties acting in concert with the acquiror, during the previous 12 months. This mandatory bid requirement is triggered if an acquisition of securities would increase the aggregate holding of an acquiror, including the holdings of any parties acting in concert with the acquiror, to securities representing 30% or more of the voting rights in a company, unless the Irish Takeover Panel otherwise consents. An acquisition of securities by a person holding, together with its concert parties, securities representing between 30% and 50% of the voting rights in a company would also trigger the mandatory bid requirement if, after giving effect to the acquisition, the percentage of the voting rights held by that person, together with its concert parties, would increase by 0.05% within a 12-month period. Any person, excluding any parties acting in concert with the holder, holding securities representing more than 50% of the voting rights of a company is not subject to these mandatory offer requirements in purchasing additional securities.

Voluntary Bid; Requirements to Make a Cash Offer and Minimum Price Requirements

        If a person makes a voluntary offer to acquire our outstanding ordinary shares, the offer price must not be less than the highest price paid for our ordinary shares by the bidder or its concert parties during the three-month period prior to the commencement of the offer period. The Irish Takeover Panel has the power to extend the "look back" period to 12 months if the Irish Takeover Panel, taking into account the General Principles, believes it is appropriate to do so.

        If the bidder or any of its concert parties has acquired our ordinary shares (1) during the 12-month period prior to the commencement of the offer period that represent more than 10% of our total ordinary shares or (2) at any time after the commencement of the offer period, the offer must be in cash or accompanied by a full cash alternative and the price per ordinary share must not be less than the highest price paid by the bidder or its concert parties during, in the case of clause (1), the 12-month period prior to the commencement of the offer period or, in the case of (2), the offer period. The Irish Takeover Panel may apply this Rule to a bidder who, together with its concert parties, has acquired less than 10% of our total ordinary shares in the 12-month period prior to the commencement of the offer period if the Irish Takeover Panel, taking into account the General Principles, considers it just and proper to do so.

        An offer period will generally commence from the date of the first announcement of the offer or proposed offer.

Substantial Acquisition Rules

        The Irish Takeover Rules also contain rules governing substantial acquisitions of shares and other voting securities which restrict the speed at which a person may increase his or her holding of shares and rights over shares to an aggregate of between 15% and 30% of the voting rights of the company. Except in certain circumstances, an acquisition or series of acquisitions of shares or rights over shares representing 10% or more of the voting rights of the company is prohibited, if such acquisition(s), when aggregated with shares or rights already held, would result in the acquirer holding 15% or more

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but less than 30% of the voting rights of the company and such acquisitions are made within a period of seven days. These rules also require accelerated disclosure of acquisitions of shares or rights over shares relating to such holdings.

Frustrating Action

        Under the Irish Takeover Rules, our board of directors is not permitted to take any action that might frustrate an offer for our shares once our board of directors has received an approach that may lead to an offer or has reason to believe that such an offer is or may be imminent, subject to certain exceptions. Potentially frustrating actions such as 1) the issue of shares, options, restricted share units or convertible securities, (2) material acquisitions or disposals, (3) entering into contracts other than in the ordinary course of business or (4) any action, other than seeking alternative offers, which may result in frustration of an offer, are prohibited during the course of an offer or at any earlier time during which our board of directors has reason to believe an offer is or may be imminent. Exceptions to this prohibition are available where:

•

the action is approved by our shareholders at a general meeting; or



•

the Irish Takeover Panel has given its consent, where:



•

it is satisfied the action would not constitute frustrating action;



•

our shareholders holding more than 50% of the voting rights state in writing that they approve the proposed action and would vote in favor of it at a general meeting;



•

the action is taken in accordance with a contract entered into prior to the announcement of the offer, or any earlier time at which our board of directors considered the offer to be imminent; or



•

the decision to take such action was made before the announcement of the offer and either has been at least partially implemented or is in the ordinary course of business.

Shareholders' Rights Plan

        Irish law does not expressly authorize or prohibit companies from issuing share purchase rights or adopting a shareholder rights plan as an anti-takeover measure. However, there is no directly relevant case law on the validity of such plans under Irish law. In addition, such a plan would be subject to the Irish Takeover Rules and the General Principles underlying the Irish Takeover Rules. Our Articles allow our board of directors to adopt a shareholder rights plan upon such terms and conditions as our board of directors deems expedient and in the best interests of us, subject to applicable law.

        Subject to the Irish Takeover Rules, our board of directors also has power to issue any of our authorized and unissued shares on such terms and conditions as it may determine and any such action should be taken in our best interests. It is possible, however, that the terms and conditions of any issue of preferred shares could discourage a takeover or other transaction that holders of some or a majority of the ordinary shares believe to be in their best interests or in which holders might receive a premium for their shares over the then-market price of the shares.

Disclosure of Interests in Shares

        Under the Irish Companies Act, our shareholders must notify us if, as a result of a transaction, the shareholder will become interested in three percent or more of our voting shares, or if as a result of a transaction a shareholder who was interested in three percent or more of our voting shares ceases to be so interested. Where a shareholder is interested in three percent or more of our voting shares, the shareholder must notify us of any alteration of his or her interest that brings his or her total holding through the nearest whole percentage number, whether an increase or a reduction. The relevant

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percentage figure is calculated by reference to the aggregate nominal value of the voting shares in which the shareholder is interested as a proportion of the entire nominal value of our issued share capital (or any such class of share capital in issue). Where the percentage level of the shareholder's interest does not amount to a whole percentage, this figure may be rounded down to the next whole number. We must be notified within five business days of the transaction or alteration of the shareholder's interests that gave rise to the notification requirement. If a shareholder fails to comply with these notification requirements, the shareholder's rights in respect of any of our shares it holds will not be enforceable, either directly or indirectly. However, such person may apply to the court to have the rights attaching to such shares reinstated.

        In addition to these disclosure requirements, we, under the Irish Companies Act, may, by notice in writing, require a person whom we know or have reasonable cause to believe to be, or at any time during the three years immediately preceding the date on which such notice is issued to have been, interested in shares comprised in our relevant share capital to (i) indicate whether or not it is the case and (ii) where such person holds or has during that time held an interest in our shares, to provide additional information, including the person's own past or present interests in our shares. If the recipient of the notice fails to respond within the reasonable time period specified in the notice, we may apply to the Irish court for an order directing that the affected shares be subject to certain restrictions, as prescribed by the Irish Companies Act, as follows:

•

any transfer of those shares or, in the case of unissued shares, any transfer of the right to be issued with shares and any issue of shares, shall be void;



•

no voting rights shall be exercisable in respect of those shares;



•

no further shares shall be issued in right of those shares or in pursuance of any offer made to the holder of those shares; and



•

no payment shall be made of any sums due from us on those shares, whether in respect of capital or otherwise.

        The court may also order that shares subject to any of these restrictions be sold with the restrictions terminating upon the completion of the sale.

        In the event we are in an offer period pursuant to the Irish Takeover Rules, accelerated disclosure provisions apply for persons holding an interest in our securities of one percent or more.

Listing

        Our ordinary shares are listed on The Nasdaq Global Select Market under the symbol "SBBP."

Transfer Agent and Registrar

        The transfer agent and registrar for our ordinary shares is Computershare, Inc. The transfer agent and registrar's address is 250 Royall Street, Canton, MA 02021.

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Differences in Corporate Law Between Ireland and the State of Delaware

        As a public limited company incorporated under the laws of Ireland, the rights of our shareholders are governed by applicable Irish law, including the Irish Companies Act, and not by the law of any U.S. state. As a result, our directors and shareholders are subject to different responsibilities, rights and privileges than are applicable to directors and shareholders of U.S. corporations. We have set below a summary of the differences between the provisions of the Irish Companies Act applicable to us and the Delaware General Corporation Law relating to stockholders' rights and protections. This summary is not intended to be a complete discussion of the respective rights and it is qualified in its entirety by reference to Irish law, Delaware law and our Articles. Before investing, you should consult your legal advisor regarding the impact of Irish corporate law on your specific circumstances and reasons for investing. The summary below does not include a description of rights or obligations under the U.S. federal securities laws or NASDAQ listing requirements. You are also urged to carefully read the relevant provisions of the Delaware General Corporation Law and the Irish Companies Act for a more complete understanding of the differences between Delaware and Irish law.

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