HORIZON THERAPEUTICS PUBLIC LIMITED COMPANY

ANNUAL GENERAL MEETING OF SHAREHOLDERS

July 27, 2023

NOTICE AND PROXY STATEMENT

June 30, 2023

Dear Fellow Shareholder:

2022 marked another impressive year for Horizon, with double-digit net sales growth across our commercial portfolio and significant progress executing on our strategy to maximize the value of our medicines, expand our global presence and advance our pipeline.

Furthermore, on December 12, 2022, we announced that we had entered into a transaction agreement (the Transaction Agreement) with Amgen Inc. (Amgen) and Pillartree Limited, a wholly owned subsidiary of Amgen. Under the Transaction Agreement, all outstanding shares of Horizon would be acquired for $116.50 per share in cash (the Transaction).⁽¹⁾ At a special meeting held on February 24, 2023, our shareholders voted on and overwhelmingly approved the Transaction. Subject to the closing of the Transaction, Horizon will become a wholly owned subsidiary of Amgen and cease to be a publicly traded company.

Over the past 15 years, Horizon has built one of the fastest growing and most respected companies in the biotechnology industry. We have accomplished a tremendous amount for patients, their families and our customers, and created significant value for our shareholders. These accomplishments are all rooted in the deep commitment, dedication and personal passion that Horizon employees have for those impacted by rare, autoimmune and severe inflammatory diseases. We go to incredible lengths to make the world a better place by addressing unmet medical needs and by building healthier communities, urgently and responsibly. We believe that Amgen is aligned with that commitment and passion, and that it will continue to maximize the value of our current portfolio and pipeline, as well as having the potential to accelerate the availability of our important rare disease medicines to more patients worldwide.

We and Amgen remain committed to closing the Transaction as soon as possible. Because the Transaction is still pending, the 2023 Annual General Meeting of Shareholders has been scheduled in order to ensure that we remain in compliance with Irish law.

The compensation information included in the Proxy Statement reflects compensation paid to or earned by our directors and named executive officers in 2022. Most of this information was previously disclosed in Part III of our Annual Report on Form 10-K for the fiscal year ended December 31, 2022, and filed with the U.S. Securities and Exchange Commission (SEC) on March 1, 2023.

You are cordially invited to attend our Annual General Meeting of Shareholders on Thursday, July 27, 2023, at 9:00 a.m. local time at our corporate headquarters, located at 70 St. Stephen’s Green, Dublin 2, D02 E2X4, Ireland. Whether or not you plan to attend, it is important that your shares be represented and voted. Please take a moment now to vote your shares using the instructions found on the proxy card and in this Proxy Statement. Your vote is important, and we appreciate your support of Horizon.

Sincerely,

Timothy P. Walbert

Chairman, President and Chief Executive Officer

Horizon Therapeutics Public Limited Company

70 St. Stephen’s Green, Dublin 2, D02 E2X4, Ireland

NOTICE OF ANNUAL GENERAL MEETING OF SHAREHOLDERS TO BE HELD ON JULY 27, 2023

Dear Shareholder:

We will be holding the Annual General Meeting of Shareholders of Horizon Therapeutics Public Limited Company on Thursday, July 27, 2023, at 9:00 a.m. local time at our corporate headquarters located at 70 St. Stephen’s Green, Dublin 2, D02 E2X4, Ireland, for the following purposes:

These items of business are more fully described in the Proxy Statement accompanying this Notice.

The Board recommends that you vote FOR each of the nominees for director named herein and FOR Proposals 2 and 3. The accompanying Proxy Statement contains additional information and should be carefully reviewed by shareholders.

Our Irish statutory financial statements for the fiscal year ended December 31, 2022, including the reports of the directors and statutory auditors thereon, will be presented at the Annual General Meeting. There is no requirement under Irish law that such statements be approved by the shareholders and no such approval will be sought at the Annual General Meeting.

For the purposes of our Articles of Association, Proposals 1 and 2 and the receipt and consideration of the Irish statutory financial statements by us at the Annual General Meeting are deemed to be ordinary business and Proposal 3 is deemed to be special business. Shareholders of record as of June 2, 2023, the record date for the Annual General Meeting, are entitled to notice of the Annual General Meeting and to vote at the Annual General Meeting or any adjournment or postponement thereof.

By Order of the Board of Directors

David Caraher

Company Secretary

Dublin, Ireland

June 30, 2023

If you are a shareholder of record on June 2, 2023, you are cordially invited to attend the Annual General Meeting in person. Whether or not you expect to attend the meeting, please complete, date, sign and return the enclosed proxy card or vote over the telephone or the internet as instructed in these materials, as promptly as possible in order to ensure your representation at the meeting. Even if you have voted by proxy, you may still vote in person if you attend the meeting. A return envelope (which is postage prepaid if mailed in the United States) has been provided for your convenience. Please note, however, that if your shares are held of record by a broker, bank or other nominee and you wish to vote at the meeting, you must obtain a proxy issued in your name from that record holder.

TABLE OF CONTENTS

QUESTIONS AND ANSWERS ABOUT THESE PROXY MATERIALS AND VOTING

This Proxy Statement contains important information regarding the Annual General Meeting of Shareholders, the proposals on which you are being asked to vote, information you may find useful in determining how to vote and voting procedures. You are invited to attend the Annual General Meeting to vote on the proposals described in this Proxy Statement. However, you do not need to attend the meeting to vote your shares.

Why am I receiving these materials?

We have sent you these proxy materials because our Board is soliciting your proxy to vote at the Annual General Meeting, including at any adjournments or postponements of the meeting. You are invited to attend the Annual General Meeting in person to vote on the proposals described in this Proxy Statement. However, you do not need to attend the meeting to vote your shares. Instead, you may simply complete, sign and return the enclosed proxy card or follow the instructions below to submit your proxy over the telephone or through the internet.

We intend to mail these proxy materials on or about June 30, 2023 to all shareholders of record as of June 2, 2023, who are entitled to vote at the Annual General Meeting.

Why is Horizon holding the Annual General Meeting?

On December 12, 2022, we announced that we had entered into a transaction agreement (the Transaction Agreement) with Amgen Inc. (Amgen) and Pillartree Limited, a wholly owned subsidiary or Amgen. Under the Transaction Agreement, all outstanding shares of Horizon would be acquired for $116.50 per share In cash (the Transaction).¹ At a special meeting held on February 24, 2023, our shareholders voted on and overwhelmingly approved the Transaction. Subject to the closing of the Transaction, Horizon will become a wholly owned subsidiary or Amgen and cease to be a publicly traded company.

On May 16, 2023, the U.S. Federal Trade Commission (the FTC) filed a complaint in the U.S. District Court for the Northern District of Illinois seeking a temporary restraining order and preliminary injunction enjoining the Transaction. In connection therewith, Horizon, Amgen and the FTC jointly proposed a temporary restraining order providing that Horizon and Amgen would not close the Transaction until the earlier of October 31, 2023 or the second business day after the court rules on the FTC’s request for a preliminary injunction (the Stipulated TRO).

Although we and Amgen remain committed to closing the Transaction as soon as possible, based on the FTC’s filing of its complaint and the related Stipulated TRO, we do not expect to close the Transaction prior to July 27, 2023, which is the latest date we may hold the Annual General Meeting under Irish law. Accordingly, we are holding the Annual General Meeting in order to ensure that-we remain in compliance with this Irish law requirement.

How do I attend the Annual General Meeting?

The meeting will be held on Thursday, July 27, 2023, at 9:00 a.m. local time at our corporate headquarters located at 70 St. Stephen’s Green, Dublin 2, D02 E2X4, Ireland. Directions to the Annual General Meeting may be found at https://www.google.com/maps/place/70+St+Stephen’s+Green,+Saint+Kevin’s,+Dublin,+Ireland. Information on how to vote in person at the Annual General Meeting is provided below. However, you do not need to attend the Annual General Meeting to vote your ordinary shares.

Who can vote at the Annual General Meeting?

Only shareholders of record at the close of business on June 2, 2023, will be entitled to vote at the Annual General Meeting. On this record date, there were 228,925,986 of our ordinary shares outstanding and entitled to vote.

Shareholder of Record (shares registered in your name). If on June 2, 2023, your shares were registered directly in your name in our Register of Members, which is maintained by our transfer agent, Computershare Shareowner Services LLC, then you are a shareholder of record. As a shareholder of record, you may vote in person at the meeting or vote by proxy. Whether or not you plan to attend the meeting, we urge you to fill out and return the enclosed proxy card, vote by proxy over the telephone or vote by proxy through the internet as discussed below to ensure your vote is counted.

Beneficial Owner (shares registered in the name of a broker or bank). If on June 2, 2023, your shares were not registered in your name in our Register of Members, but rather held in an account at a brokerage firm, bank, dealer or other similar organization,

then you are the beneficial owner of shares held in “street name” and these proxy materials are being forwarded to you by that organization. The organization holding your account is considered to be the shareholder of record for purposes of voting at the Annual General Meeting. As a beneficial owner, you have the right to direct your broker or other agent regarding how to vote the shares in your account. You are also invited to attend the Annual General Meeting. However, since you are not the shareholder of record, you may not vote your shares in person at the meeting unless you request and obtain a valid proxy from your broker, bank or other agent.

What am I voting on?

There are three matters scheduled for a vote:

What if another matter is properly brought before the meeting?

The Board knows of no other matters that will be presented for consideration at the Annual General Meeting. If any other matters are properly brought before the meeting, it is the intention of the persons named in the accompanying proxy to vote on those matters in accordance with their best judgment.

How do I vote?

You may vote “For” or “Against” each Class III director nominee or you may abstain from voting for all or any of the nominees. For each of the other matters to be voted on, you may vote “For” or “Against” or abstain from voting.

The procedures for voting are fairly simple:

Shareholder of Record. If you are a shareholder of record, you may vote in person at the Annual General Meeting, vote by proxy using the enclosed proxy card, vote by proxy over the telephone or vote by proxy through the internet as instructed below. Whether or not you plan to attend the meeting, we urge you to vote by proxy to ensure your vote is counted. You may still attend the meeting and vote in person even if you have already voted by proxy.

We provide internet proxy voting to allow you to vote your shares online, with procedures designed to ensure the authenticity and correctness of your proxy vote instructions. However, please be aware that you must bear any costs associated with your internet access, such as usage charges from internet access providers and telephone companies.

Beneficial Owner. If you are a beneficial owner of shares registered in the name of your broker, bank or other agent, you should have received a voting instruction form with these proxy materials from that organization rather than from Horizon. To vote prior to the meeting, simply complete and mail the voting instruction form to ensure that your vote is counted. Alternatively, you may vote by telephone or through the internet as instructed by your broker, bank or other agent. To vote in person at the Annual General Meeting, you must obtain a valid proxy from your broker, bank or other agent. Follow the instructions from your broker, bank or other agent included with these proxy materials, or contact that organization to request a proxy form.

Joint Holders. In the case of joint holders of record, any one of such holders may vote either in person or by proxy in respect thereof as if he or she were the sole holder thereof, but the vote of the senior holder who tenders a vote, whether in person or by proxy, shall be accepted to the exclusion of the votes of the other joint holders, and for this purpose seniority shall be determined by the order in which the names stand in our Register of Members.

How many votes do I have?

On each matter to be voted upon, you have one vote for each ordinary share you own as of June 2, 2023.

What happens if I do not vote?

Shareholder of Record. If you are a shareholder of record and do not vote by completing your proxy card, by telephone, through the internet or in person at the Annual General Meeting, your shares will not be voted.

Beneficial Owner. If you are a beneficial owner and do not instruct your broker, bank or other agent how to vote your shares, the question of whether your broker or nominee will still be able to vote your shares depends on whether the New York Stock Exchange (NYSE) deems the particular proposal to be a “routine” matter. Brokers and nominees can use their discretion to vote “uninstructed” shares with respect to matters that are considered to be “routine,” but not with respect to “non-routine” matters. Under the rules and interpretations of the NYSE, “non-routine” matters are matters that may substantially affect the rights or privileges of shareholders, such as mergers, shareholder proposals, elections of directors (even if not contested), executive compensation (including any advisory shareholder votes on executive compensation) and certain corporate governance proposals, even if management-supported. We understand that under NYSE rules, your broker or nominee may not vote your shares on Proposals 1 or 3 without your instructions but may vote your shares on Proposal 2.

What if I return a proxy card or otherwise vote but do not make specific choices?

If you return a signed and dated proxy card or otherwise vote without marking voting selections, then our designated proxy holders (one of the individuals named on your proxy card) will vote your shares in the manner recommended by our Board on all matters presented in this Proxy Statement and as the proxy holders may determine in their discretion regarding any other matters properly presented for a vote at the meeting. If any other matter is properly presented at the meeting, your proxy holder will vote your shares using his or her best judgment.

Who is paying for this proxy solicitation?

The cost of soliciting proxies incurred by us, including the preparation, assembly and mailing of proxy materials, as well as the cost of forwarding such material to beneficial owners of our ordinary shares, will be borne by us. Our directors, officers and other employees may, without compensation other than their regular remuneration, solicit proxies personally or by telephone.

What does it mean if I receive more than one set of proxy materials?

If you receive more than one set of proxy materials, your shares may be registered in more than one name or in different accounts. Please follow the voting instructions on the proxy cards in the proxy materials to ensure that all of your shares are voted.

Can I change my vote after submitting my proxy?

Shareholder of Record. Yes, you may revoke your proxy at any time before the final vote at the meeting. If you are the record holder of your shares, you may revoke your proxy in any one of the following ways:

Your most current proxy card or telephone or internet proxy is the one that is counted.

Beneficial Owner. If your shares are held by your broker or bank as a nominee or agent, you should follow the instructions provided by your broker or bank.

Do I need a ticket to attend the Annual General Meeting?

Yes, you will need an admission ticket or proof of ownership of ordinary shares to enter the Annual General Meeting. If you are a shareholder of record, your admission ticket is attached to the proxy card sent to you. Please bring your proxy card and valid photo identification with you to the Annual General Meeting. If your shares are held in the name of a bank, broker or other holder of record, your admission ticket is on your voting instruction form. If you do not bring your admission ticket, you will need proof of ownership of ordinary shares to be admitted to the Annual General Meeting. A recent brokerage statement or letter from a bank or broker is an example of proof of ownership. If you arrive at the Annual General Meeting without an admission ticket or proof of ownership of ordinary shares, we will admit you only if we are able to verify that you are one of our shareholders.

How are votes counted?

Votes will be counted by the inspector of election appointed for the meeting, who will separately count, with respect to the proposal to elect directors, votes “For,” “Against,” abstentions and broker non-votes; and, with respect to other proposals, votes “For” and “Against,” abstentions and, as applicable, broker non-votes. Abstentions and broker non-votes will be treated as shares present for the purpose of determining the presence of a quorum for the transaction of business at the Annual General Meeting. Abstentions and broker non-votes will not, however, be considered votes cast at the Annual General Meeting. Because the approval of all of the proposals is based on the votes cast at the Annual General Meeting, abstentions and broker non-votes will not have any effect on the outcome of voting on the proposals.

What are “broker non-votes”?

As discussed above, when a beneficial owner of shares held in “street name” does not give instructions to the broker or nominee holding the shares as to how to vote on matters deemed by the NYSE to be “non-routine,” the broker or nominee cannot vote the shares. These un-voted shares are counted as “broker non-votes.”

What is the quorum requirement?

A quorum of shareholders is necessary to hold a valid meeting. A quorum will be present if shareholders holding a majority of the issued and outstanding ordinary shares entitled to vote are present at the meeting in person or represented by proxy. On the record date, there were 228,925,986 ordinary shares outstanding and entitled to vote. Thus, the holders of 114,462,994 ordinary shares must be present in person or represented by proxy at the meeting to have a quorum.

Your shares will be counted towards the quorum only if you submit a valid proxy (or one is submitted on your behalf by your broker, bank or other nominee) or, provided that you are a shareholder of record, if you vote in person at the meeting. Abstentions and broker non-votes will be counted towards the quorum requirement. If there is no quorum, within one hour of the time appointed for the Annual General Meeting, the Annual General Meeting will stand adjourned to August 3, 2023, at 9:00 a.m. local time at the same location, or such other time or place as the Board may determine.

Assuming there is a quorum of shares present at the Annual General Meeting, how many votes are needed to approve each proposal?

How can I find out the results of the voting at the Annual General Meeting?

Preliminary voting results will be announced at the Annual General Meeting. In addition, final voting results will be published in a current report on Form 8-K that we expect to file within four business days after the Annual General Meeting. If final voting results are not available to us in time to file a Form 8-K within four business days after the meeting, we intend to file a Form 8-K to publish preliminary results and, within four business days after the final results are known to us, file an additional Form 8-K to publish the final results.

What are the Irish statutory financial statements?

We are presenting our Irish statutory financial statements, including the reports of the directors and the statutory auditors thereon, at the Annual General Meeting and are making a copy available for download on the Annual Reports / Proxy Statements

page in the Investors section of our website (www.horizontherapeutics.com) on or before July 5, 2023. As an Irish company, we are required to prepare Irish statutory financial statements under applicable Irish company law and to deliver those accounts to shareholders of record in connection with our Annual General Meetings. The Irish statutory financial statements cover the results of our operations and financial position for the year ended December 31, 2022.

Irish law requires the directors to prepare financial statements for each financial year giving a true and fair view of the state of the group’s and parent company’s affairs at the end of the financial year and of the group’s profit or loss for the financial year. Under that law, the directors have prepared the group’s consolidated financial statements in accordance with U.S. accounting standards, as defined in Section 279 of the Irish Companies Act 2014, to the extent that the use of those accounting standards in the preparation of the consolidated financial statements does not contravene any provision of the Irish Companies Act 2014 or of any regulations made thereunder and have prepared Horizon’s parent company’s Irish statutory financial statements in accordance with accounting standards issued by the Financial Reporting Council and promulgated by the Institute of Chartered Accountants in Ireland (Generally Accepted Accounting Practice in Ireland).

What proxy materials are available on the internet?

This Proxy Statement, our Annual Report on Form 10-K for the fiscal year ended December 31, 2022, and our annual report to shareholders are available on the Annual Reports / Proxy Statements page in the Investors section of our website (www.horizontherapeutics.com). The Irish statutory financial statements will be available on the Annual Reports / Proxy Statements page in the Investors section of our website (www.horizontherapeutics.com) on or before July 5, 2023. We will mail without charge, upon written request, a copy of these materials to shareholders of record or beneficial owners of our ordinary shares. Requests should be sent to: Horizon Therapeutics plc, Attention: Company Secretary, 70 St. Stephen’s Green, Dublin 2, D02 E2X4, Ireland.

PROPOSAL 1

ELECTION OF DIRECTORS

The Board is divided into three classes. Each class consists, as nearly as possible, of one-third of the total number of directors and each class has a three-year term. The Board currently consists of nine members, as follows:

The authorized number of directors may be changed only by resolution of the Board. Any additional directorships resulting from an increase in the number of directors will be distributed between the three classes so that, as nearly as possible, each class will consist of one-third of the directors. This classification of the Board may have the effect of delaying or preventing changes in our control or management. Our directors may be removed by ordinary resolution with majority vote of our shareholders at a general meeting provided that notice of such resolution has been given in accordance with Section 146 of the Irish Companies Act 2014. Vacancies on the Board may be filled only by persons elected by a majority of the directors then in office, provided that a quorum is present. A director elected by the Board to fill a vacancy in a class, including vacancies created by an increase in the number of directors, shall serve for the remainder of the full term of that class and until the director’s successor is duly elected and qualified.

Majority Voting: In order to be elected as a director, each nominee must receive the affirmative vote of a majority of the votes cast by the holders of ordinary shares represented at the Annual General Meeting in person or by proxy.

Directors Whose Term of Office is Set to Expire at the Annual General Meeting: There are currently three directors in Class III whose term of office is set to expire at the Annual General Meeting. Each of the nominees listed below in Class III is currently a director who was nominated for election by the Board, upon the recommendation of the Nominating and Corporate Governance Committee. If elected, each of these nominees would be elected to serve for a term set to expire at the 2026 Annual General Meeting of Shareholders.

Effect of the Transaction: If the closing of the Transaction with Amgen occurs, we will become a wholly owned subsidiary of Amgen and cease to be a publicly traded company. Accordingly and pursuant to the Transaction Agreement with Amgen, if the closing occurs, the resignation from the Board of each of our current directors, including the Class III nominees, would occur and persons nominated by Amgen will be appointed to the Board. If the closing of the Transaction does not occur, each of the Class III nominees, if elected at the Annual General Meeting, would continue to serve until the 2026 Annual General Meeting of Shareholders and until their successor has been duly elected and qualified, or, if sooner, until the director’s death, resignation, disqualification or removal.

The biographical information for our directors that follows is as of May 31, 2023.

Summary: Director Nominees and Continuing Directors

Board Highlights

The Nominating and Corporate Governance Committee of our Board examines multiple factors when evaluating directors, including their knowledge, skills and experience, including experience in our industry and with respect to clinical development, sales and marketing, business development, finance, management and public service. The tables below highlight the diversity and extensive experience of our directors as well as the balance of skills on our Board:

Our Board of Directors: Gender and Ethnicity Diversity Matrix⁽¹⁾

As of May 31, 2023

Our Board of Directors: Skills and Experience Matrix

THE BOARD RECOMMENDS

A VOTE IN FAVOR OF EACH NAMED NOMINEE ABOVE

THE BOARD OF DIRECTORS AND ITS COMMITTEES

In 2022, the Board held 13 meetings and did not act by unanimous written consent without a meeting. Each Board member attended 86% or more of the aggregate number of meetings of the Board and of the committees on which he or she served that were held during the portion of the last fiscal year for which he or she was a director or committee member. It is our policy to encourage directors and nominees for director to attend annual general meetings of shareholders. All current directors attended our 2022 Annual General Meeting of Shareholders.

The Board is committed to exercising good corporate governance practices. As part of this commitment, the Board regularly monitors developments in corporate governance and reviews processes, policies and procedures in light of such developments. Key information regarding our corporate governance initiatives can be found on our website, www.horizontherapeutics.com, including our Memorandum and Articles of Association, Code of Conduct and Ethics, Corporate Governance Guidelines, and the charters for the Audit, Compensation, Nominating and Corporate Governance, Scientific and Transaction Committees. The Board believes that its strong corporate governance policies and practices, including the substantial percentage of independent directors on the Board and the robust duties of its lead independent director, empower the Board to effectively oversee our chief executive officer and provide an effective and appropriately balanced Board governance structure.

Other than Mr. Walbert, our chairman, president and chief executive officer, all members of the Board are independent, and all members of committees of the Board are independent. The Board has affirmatively determined that the following eight directors are independent directors within the meaning of the applicable Nasdaq Stock Market (Nasdaq) listing standards: Mr. Daniel, Mr. Grey, Dr. Himawan, Dr. Mahony, Mr. Santini, Dr. Shannon, Mr. Watkins and Ms. Witz. In making these determinations, the Board found that none of these directors or nominees for director had a material or other disqualifying relationship with us. Mr. Walbert is not an independent director by virtue of his current employment with us. To determine independence, the Board reviewed all relevant identified transactions or relationships between each director, or any of his or her family members, and us, our senior management and our independent registered public accounting firm.

As required under applicable Nasdaq listing standards, our independent directors met four times in regularly scheduled executive sessions in 2022, at which only independent directors were present.

We have adopted a Code of Conduct and Ethics (the Code of Conduct) that applies to all officers, directors and employees, including our principal executive officer, principal financial officer, principal accounting officer and persons performing similar functions. We introduced a revised, principles-based Code of Conduct in 2021 that provides an instructive set of principles, guidelines and tools to operate our business in an ethical and compliant way. The Code of Conduct is available in the investor relations section of our website at www.horizontherapeutics.com. Information found on, or accessible through, our website is not a part of, and is not incorporated into this Proxy Statement. If we make any substantive amendments to the Code of Conduct or grant any waiver from a provision of the Code of Conduct to any executive officer or director, we will promptly disclose the nature of the amendment or waiver on our website or in a current report on Form 8-K.

The Board has determined that the current leadership structure, in which the offices of chairman and chief executive officer are held by one individual and an independent director acts as lead independent director, ensures that the appropriate level of oversight, independence and responsibility is applied to all Board decisions, including risk oversight, and is in our best interests and those of our shareholders.

Chairman/Chief Executive Officer

The Board is currently chaired by our president and chief executive officer, Mr. Walbert. We believe that combining the positions of chief executive officer and chairman of the Board helps to ensure that the Board and management act with a common purpose for the following reasons:

Lead Independent Director

We require the election, by the independent directors of the Board, of a lead independent director to serve during any period when there is no independent chairman of the Board. Because Mr. Walbert is currently serving as chief executive officer and chairman of the Board, the independent directors of the Board elected Mr. Grey as the lead independent director. The lead independent director serves as the liaison between the chairman of the Board and the independent directors. The responsibilities of the lead independent director include:

One of the Board’s key functions is informed oversight of our risk management process. The Board does not have a standing risk management committee, but rather administers this oversight function directly through the Board as a whole, as well as through various Board standing committees that address risks inherent in their respective areas of oversight. In particular, the Board is responsible for monitoring and assessing strategic risk exposure, including a determination of the nature and level of risk appropriate for Horizon.

Our Audit Committee has the responsibility to consider and discuss our major financial risk exposures and the steps our management has taken to monitor and control these exposures, including guidelines and policies to govern the process by which financial risk assessment and management is undertaken and provides oversight of the performance of our internal audit function and external auditors. The Audit Committee also reviews and receives regular briefings concerning information security and technology risks.

Our Compensation Committee assesses and monitors whether any of our compensation policies and programs has the potential to encourage excessive risk-taking.

Our Nominating and Corporate Governance Committee reviews our key enterprise risks and risk-management strategies, as well as monitors the effectiveness of our corporate governance guidelines, including whether they are successful in preventing illegal or improper liability-creating conduct, and monitors compliance with legal, regulatory and ethical requirements.

Our Scientific Committee reviews our R&D programs and evaluates R&D opportunities from a scientific perspective, including the risks related to such matters.

Our Transaction Committee evaluates potential strategic transactions and financing opportunities, including the risks that such transactions could pose to Horizon.

Cybersecurity

Horizon is committed to protecting our company’s information technology systems. We manage information technology (IT) systems that facilitate commercial, supply chain and regulatory activities; maintain our financial data; and store employee and customer data. We have protocols, policies and tools in place to mitigate cybersecurity risk. They also provide the administrative, technical, and physical safeguards to ensure the security, confidentiality, integrity and availability of confidential information and personal information from unauthorized access, use, disclosure, alteration, destruction or theft. In addition, we engage an independent third party annually to assess our IT general controls and IT security. The Audit Committee and full Board is briefed by our chief information officer at least twice a year on our cybersecurity risk management programs and the overall

cybersecurity risk environment. The briefing includes discussions on topics such as information security and technology risks, cybersecurity, information risk management strategies and progress and cybersecurity and data protection training initiatives for employees, among others. To our knowledge, we have not experienced a material information security breach nor incurred any penalties or settlements regarding information security.

Pascale Witz, one or our Board members, holds a CERT Certificate in Cybersecurity Oversight from the Software Engineering Institute of Carnegie Mellon University and the National Association of Corporate Directors. H. Thomas Watkins, also a Board member, is in the process of obtaining the same cybersecurity oversight certification.

The Nominating and Corporate Governance Committee believes that a strong director assessment process and periodic Board refreshment enhances the effectiveness of the Board and is an essential element of sound corporate governance.

Director assessment is conducted on an annual basis at both the full Board and individual director level:

Annual Board Member Self-Assessment: The director self-assessment process typically begins in August, when a telephonic survey is conducted with each director by a third party, generally a partner from our external legal counsel. The telephonic survey, which is updated annually, allows the interviewer to more fully assess and understand the needs, comments and patterns resulting from the individual conversations. This interview process elicits each director’s opinions on the overall effectiveness of the Board and its committees, the information the Board receives, the conduct of Board meetings, communication among directors and management, the oversight of key business risks and environmental, social and governance issues, Board composition, and any other matters that any director wishes to raise. The results are summarized in an anonymous matter and reviewed by the Nominating and Corporate Governance Committee during its fourth-quarter meeting and key findings and observations are reported to the full Board for discussion and action, if appropriate. This process has resulted in several meaningful improvements to the effectiveness of our Board meetings and timing and means of providing information to the Board.

Annual Board Member Review: A thorough and in-depth review is conducted for the directors whose term will expire at the next annual general meeting of shareholders. The review assesses each director based on his or her Board and committee experience to date and the skills and experiences deemed appropriate to meet the current and future needs of Horizon and the Board. The review consists of a three-part process to determine if each director should seek another three-year term.

As a result of our Board assessment process, since 2017, two prior directors did not stand for re-election and three new directors have been added to the Board. Each of our new directors, two of whom are female, have brought new and different skills, experience and qualifications to the Board.

The Nominating and Corporate Governance Committee employs a rigorous, thorough and in-depth process to identify director candidates and recommend the strongest possible director nominees to the full Board.

First, the Nominating and Corporate Governance Committee deliberates on and determines the skills and experience that would best serve the Board and Horizon and that would address any gaps identified in the annual assessment process.

An executive search firm is then retained to assist in identifying prospective candidates. In addition, the Nominating and Corporate Governance Committee considers director candidates recommended by shareholders, directors and other sources. Shareholders who wish to recommend individuals for consideration by the Nominating and Corporate Governance Committee to become nominees for election to the Board at an annual general meeting may do so by delivering a written recommendation to the Nominating and Corporate Governance Committee no later than the close of business on the 90th day nor earlier than the

close of business on the 150th day prior to the first anniversary of the date our proxy statement was first released to shareholders in connection with the preceding year’s annual general meeting at Horizon Therapeutics plc, 70 St. Stephen’s Green, Dublin 2, D02 E2X4, Ireland, Attention: Company Secretary. Submissions must include the same information required for the shareholder nomination of persons to be elected to the Board at an annual general meeting set forth in “Other information – Shareholder Proposals” in this Proxy Statement. Any such submission must be accompanied by the written consent of the proposed nominee to be named as a nominee and to serve as a director if elected. In the event that the date of an annual general meeting is changed by more than 30 days from the first anniversary date of the prior year’s annual general meeting, such written recommendation must be delivered not earlier than the 150th day prior to such annual general meeting and not later than the later of the 90th day prior to such annual general meeting or the 10th day following the day on which public announcement of the date of such annual general meeting is first made. The Nominating and Corporate Governance Committee does not intend to alter the manner in which it evaluates candidates based on whether the candidate was recommended by a shareholder or not.

When selecting candidates for recommendation to the Board, the Nominating and Corporate Governance Committee consider the attributes of the candidates and the needs of the Board and reviews all candidates in the same manner, regardless of the source of the recommendation. In evaluating director nominees, a candidate is expected to have certain minimum qualifications, including being able to read and understand basic financial statements, having familiarity with our business and industry, having high moral character and mature judgment and being able to work collegially with others. In addition, factors such as the following may be considered:

Before the Nominating and Corporate Governance Committee recommends a qualified director nominee to the Board for consideration, the nominee is interviewed by each Board member and meets with the chief executive officer and other senior executives.

The Nominating and Corporate Governance Committee and the Board believe that all directors should have sufficient time and attention to devote to Board duties and to otherwise fulfill the responsibilities required of directors. In assessing whether directors and nominees for director have sufficient time and attention to devote to Board duties, the Nominating and Corporate Governance Committee considers, among other things, whether directors may be “overboarded,” which refers to the situation where a director serves on an excessive number of boards. Our Corporate Governance Guidelines also require that non-employee directors seek approval from the Chairman or the lead independent director in advance of accepting an invitation to serve on any additional corporate boards or board committee of another company. Management members of the Board must advise the lead independent director and consult with the Chair of the Nominating and Corporate Governance Committee in advance of accepting an invitation to serve on the board of another company and should only do so to the extent such service would not detract from his or her ability to fulfill his or her management functions at the Company. The Nominating and Corporate Governance Committee and our Board believe that each of our directors has demonstrated the ability to devote sufficient time and attention to Board duties and to otherwise fulfill the responsibilities required of directors.

At our 2022 Annual General Meeting of Shareholders, Michael Grey, our lead independent director who was standing for election, received a lower level of support than the other two directors standing for election, which we believe was due primarily to one proxy advisory firm deeming Mr. Grey to be “overboarded” in light of his other public company board commitments.

During our subsequent outreach to shareholders, we shared our belief that Mr. Grey’s commitment to our Board has not been impacted by his outside obligations, and that he continues to demonstrate excellence in his performance as a member and lead independent director of our Board. Specifically, we noted: his perfect attendance record at all of our Board and relevant committee meetings for the previous three years (aside from a conflict-of-interest recusal in 2021) as well as the regularly scheduled meetings with the CEO in between Board meetings; he does not hold any committee membership roles on his other public company boards; and that none of the other public company boards have cited concerns with Mr. Grey’s performance or ability to fulfill his obligations. During the discussions, shareholders acknowledged Mr. Grey’s past contributions and commitment to our Board and did not indicate any expectation of immediate action on the part of Horizon or Mr. Grey as a result of his other public company board engagements.

Tim Walbert, our chairman, president and chief executive officer, who is standing for election at our 2023 Annual General Meeting, serves on two outside boards of public companies. Mr. Walbert takes his commitment to our Company very seriously and carefully considers his outside board commitments and the time each involves. He is confident in being able to meet the commitments for Horizon as well as the other companies on whose boards he serves. He continues to prove his ability as a strong chief executive officer and chairman of the Horizon Board, and Horizon’s performance while he has served on the outside boards supports his confidence. It is the belief of the Nominating and Corporate Governance Committee, as well as that of our Lead Independent Director Michael Grey, that Mr. Walbert’s commitment to the Board and Horizon have not been unfavorably impacted by his outside obligations. His strong leadership and focus on execution have generated substantial value for our shareholders. Furthermore, his service on the other boards broadens his experience, knowledge and insights, which in turn enhances his role as chief executive officer of Horizon.

The Board believes that maintaining a diverse membership enhances the Board’s deliberations and enables the Board to better represent all of Horizon’s constituents, and as such has a formal diversity policy. As part of the policy, the Nominating and Corporate Governance Committee annually reviews the tenure, performance and contributions of existing Board members to the extent they are candidates for re-election and considers all aspects of each candidate’s qualifications and skills with the goal of ensuring the Board has diversity of experience and perspectives as well as race, gender, geography, and areas of expertise. To further this goal, the Board is committed to including in each director search highly qualified candidates who reflect diverse experiences and backgrounds, including diversity of gender and race. The diversity policy is available on our website at www.horizontherapeutics.com. The Nominating and Corporate Governance Committee and the Board assesses the effectiveness of our diversity policy through its periodic evaluation of the composition of the full Board.

Shareholders who wish to recommend individuals for consideration by the Nominating and Corporate Governance Committee to become nominees for election to the Board at an Annual General Meeting of Shareholders must do so by delivering a written recommendation to the Nominating and Corporate Governance Committee. See the “Director Selection” section of this Proxy Statement above for additional information.

The Board has five standing committees:

All committees comprise independent directors within the meaning of the applicable Nasdaq listing standards. A description of each committee of the Board is provided below.

The following table provides membership and meeting information for fiscal year 2022 for each of the Board committees:

Audit

Compensation

Nominating and Corporate Governance

Scientific(1)

Transaction

Timothy P. Walbert

William F. Daniel

Michael Grey ( )

Jeff Himawan, Ph.D.

Susan Mahony, Ph.D.

Gino Santini

James Shannon, M.D.

H. Thomas Watkins

Pascale Witz

Total meetings in fiscal year 2022

5

9

4

3

7

= Chair		= Member		= Lead Independent Director

Audit Committee

The Audit Committee assists the Board in fulfilling its oversight responsibility with respect to, among other things:

The independent registered public accounting firm, internal audit and management each periodically meet privately with the Audit Committee.

The Board has determined that each of Mr. Daniel, Mr. Grey, Mr. Watkins and Ms. Witz meets the independence requirements of Rule 10A-3 of the Exchange Act and the Nasdaq listing standards with respect to Audit Committee members. The Board has also determined that each of Mr. Daniel, Mr. Grey, Mr. Watkins and Ms. Witz qualify as an “audit committee financial expert” within the meaning of applicable SEC rules. In making this determination, the Board has considered their formal education, the nature and scope of their previous experience and their financial and corporate governance expertise. Each of our independent registered public accounting firm, internal audit and management periodically meet privately with our Audit Committee.

Report of the Audit Committee of the Board of Directors

The material in this report is not “soliciting material,” is not deemed “filed” with the SEC and is not to be incorporated by reference in any of our filings under the Securities Act of 1933, as amended (the Securities Act), or the Securities Exchange Act of 1934, as amended (Exchange Act), whether made before or after the date hereof and irrespective of any general incorporation language in any such filing.

The Audit Committee has reviewed and discussed the audited financial statements for the year ended December 31, 2022, with Horizon management. The Audit Committee has discussed with the independent registered public accounting firm the matters required to be discussed by Auditing Standard No. 1301, Communications with Audit Committees, as adopted by the Public

Company Accounting Oversight Board (PCAOB). The Audit Committee has also received the written disclosures and the letter from the independent registered public accounting firm required by applicable requirements of the PCAOB regarding the independent registered public accounting firm’s communications with the Audit Committee concerning independence and has discussed with the independent registered public accounting firm the accounting firm’s independence. Based on the foregoing, the Audit Committee has recommended to the Board that the audited financial statements be included in Horizon’s Annual Report on Form 10-K for the fiscal year ended December 31, 2022.

Audit Committee

William F. Daniel, Chair

Michael Grey

H. Thomas Watkins

Pascale Witz

Compensation Committee

The Compensation Committee:

In making its compensation decisions and recommendations, the Compensation Committee may take into account the recommendations of the chief executive officer and other senior management. Other than giving such recommendations, however, the chief executive officer and other senior management have no formal role and no authority to determine the amount or form of executive and director compensation. The processes and procedures used by the Compensation Committee for the consideration and determination of executive compensation are described in the section of this Proxy Statement captioned, ‘‘Compensation Discussion and Analysis – Setting Executive Compensation.’’

The Compensation Committee may, at our expense, retain legal counsel (which may, but need not be, our regular corporate counsel) and other consultants and advisors, other than in-house legal counsel and certain other types of advisors, to assist it with its functions only after taking into consideration six factors, prescribed by the SEC and Nasdaq, that bear upon the advisor’s independence; however, there is no requirement that any advisor be independent. The Compensation Committee has authority to approve such advisors’ fees and other retention terms and to terminate its relationship with any advisor that it retains. In addition, the Compensation Committee has authority to delegate its responsibilities to subcommittees or individual committee members.

The Compensation Committee has engaged Aon’s Human Capital Solutions practice, a division of Aon plc (Aon), as its independent consultant since 2016. For additional information regarding our processes and procedures for the consideration and determination of executive and director compensation, including the role of Aon in determining and recommending executive and director compensation and the aggregate cost of Aon’s executive and director compensation consulting services during 2022, see the sections of this Proxy Statement entitled “Compensation Discussion and Analysis – Setting Executive Compensation” and “Non-Employee Director Compensation.” With respect to non-employee director compensation matters, our Compensation Committee recommends to our Board and our Board determines and sets non-employee director compensation. Our compensation arrangements for our non-employee directors are described under the section of this Proxy Statement entitled “Non-Employee Director Compensation.”

Compensation Committee Interlocks and Insider Participation

No member of our Compensation Committee has ever been an executive officer or employee of Horizon. None of our executive officers currently serves, or has served during the last completed year, on the compensation committee or board of directors of any other entity that has one or more officers serving as a member of our Board or Compensation Committee.

Nominating and Corporate Governance Committee

The Nominating and Corporate Governance Committee oversees all aspects of our corporate governance functions on behalf of the Board, including, but not limited to:

The process used by the Nominating and Corporate Governance Committee to identify a nominee to serve as a member of the Board depends on the qualities being sought. The Board engages an executive search firm to assist the Nominating and Corporate Governance Committee in identifying individuals qualified to be Board members. The process used by the Nominating and Corporate Governance Committee to identify nominees is described in the section of this Proxy Statement captioned, ‘‘Director Selection” above.

Scientific Committee

The functions of the Scientific Committee include, but are not limited to:

Transaction Committee

The functions of the Transaction Committee include, but are not limited to:

Shareholders who wish to communicate with the Board may do so by sending written communications addressed to the Company Secretary of Horizon Therapeutics plc at 70 St. Stephen’s Green, Dublin 2, D02 E2X4, Ireland or by communicating online to the Board as a group. This information and an online communications form are available on our website at www.horizontherapeutics.com. Each communication will be reviewed by our Company Secretary to determine whether it is appropriate for presentation to the Board or such director on a periodic basis. Examples of inappropriate communications include advertisements, solicitations or hostile communications.

NON-EMPLOYEE DIRECTOR COMPENSATION

Our directors perform a critical role in guiding Horizon’s strategic direction and overseeing management. Being a director entails many responsibilities and a substantial time commitment. Our compensation program for our non-employee directors reflects the critical function they perform and enables us to attract and retain highly qualified directors.

All current non-employee members of the Board are independent. Non-employee directors receive a combination of annual cash retainers and restricted stock unit (RSU) grants in amounts that correlate to their responsibilities and levels of Board participation, including service on Board committees. Our only employee director, Mr. Walbert, receives no separate compensation for his service as a director or chairman of the Board.

Highlights

Peer Groups

As an Irish headquartered company traded in the United States, we consider our non-employee director compensation, both in amount and structure, against two peer groups:

Jazz Pharmaceuticals plc is in both peer groups.

Compensation Program

Our Compensation Committee reviews the compensation for our non-employee directors annually. To assist with the review, Aon, an independent compensation consultant, prepares a comprehensive assessment of our non-employee director compensation program, which includes:

As part of the most recent review, conducted in October 2022, our Compensation Committee determined that:

Cash Compensation

Our compensation policy for non-employee directors who are not affiliated with any holder of more than 5% of our ordinary shares provides for annual cash compensation as set forth in the following table. The cash compensation is generally payable in equal quarterly installments at the end of each quarter in which the services are provided. For any independent director who joins after the beginning of the quarter, the cash compensation is pro-rated based on days served in that first partial quarter.

Under our compensation policy, we reimburse our directors for their travel-related expenses, including lodging and other reasonable expenses incurred in attending meetings of the Board and committees of the Board.

Equity Compensation

On the date of each Annual General Meeting of Shareholders that coincides with or follows the non-employee director’s initial appointment or election to the Board, eligible non-employee directors will automatically be granted RSUs with an aggregate value of $400,000, which will vest in full upon the earlier of the (i) first anniversary of the date of grant and (ii) date of the next Annual General Meeting of Shareholders.

Any eligible non-employee director who is first elected or appointed to the Board on any date other than an Annual General Meeting of Shareholders will automatically be granted RSUs on the date that they are first elected or appointed to the Board with a value equal to the annual RSU grant, prorated based on the number of days between such non-employee director’s start date and the one-year anniversary of the date of the Annual General Meeting of Shareholders that most recently preceded such start date, which will vest in full upon the earlier of (i) the first anniversary of the date of the Annual General Meeting of Shareholders that most recently preceded such director’s start date and (ii) the date of the next Annual General Meeting of Shareholders.

Non-Employee Director Compensation Table

The following table sets forth compensation information for our non-employee directors who earned or received compensation under our compensation policy for non-employee directors or otherwise in 2022:

Non-Employee Director Share Ownership Guidelines

We have share ownership guidelines for our non-employee directors. The share ownership guidelines were amended in October 2021 and require that each director accumulate an ownership interest in our ordinary shares with a value equal to at least 5x the annual cash board service retainer within five years of the date the non-employee director first becomes subject to the guidelines.

Individual ownership interest versus the guidelines is reviewed annually using an average share price for a calendar quarter prior to the review date. Shares that count toward satisfaction of these guidelines include: shares owned outright by the individual (including stock units that have vested but not yet settled); shares subject to RSUs that have not vested; and shares held in trust for the benefit of the individual or his/her spouse.

All of our non-employee directors subject to the share ownership guidelines met the guidelines as of December 31, 2022.

EXECUTIVE OFFICERS

The following table sets forth information regarding executive officers as of May 31, 2023:

The following biographical information for our executive officers other than Mr. Walbert, whose biographical information is included in Proposal 1, is as of May 31, 2023.

Executive Officers

Sean M. Clayton. Mr. Clayton has served as our executive vice president, general counsel since February 2022. Prior to joining Horizon, Mr. Clayton was a partner at Cooley LLP, a global law firm, where he practiced from October 2004 until February 2022, most recently as the head of the firm’s San Diego corporate practice. Before that, Mr. Clayton served as a law clerk to Judge Irma E. Gonzalez (Ret.) of the U.S. District Court for the Southern District of California. Mr. Clayton received a bachelor of arts degree in political science and economics from the University of California, San Diego and a juris doctorate degree from Stanford Law School.

Aaron L. Cox. Mr. Cox has served as our executive vice president, chief financial officer since May 2022. Mr. Cox previously served as executive vice president, finance from November 2021 to May 2022; as senior vice president, corporate development, in addition to serving as chief of staff for Timothy P. Walbert, from July 2017 to November 2021; as senior director, business development, from May 2017 to July 2017 and as director, business development from April 2016 to May 2017. Prior to joining Horizon in April 2016, Mr. Cox served as vice president, capital markets at BMO Capital Markets from July 2012 to April 2016, and before that, he held investment banking roles at Stout from 2007 to 2010 and JMP Securities from 2005 to 2006. Mr. Cox received a master of business administration from the University of Chicago and a bachelor of business administration in finance from the University of Notre Dame.

Michael A. DesJardin. Mr. DesJardin has served as our executive vice president, technical operations and corporate quality since February 2017. Mr. DesJardin previously served as our senior vice president, technical operations from October 2016 to November 2016 and as our senior vice president, life cycle management from December 2016 to January 2017. Mr. DesJardin joined Horizon from Raptor Pharmaceutical Corp. (Raptor), a public biopharma company, in October 2016 as part of the Raptor acquisition. While at Raptor, Mr. DesJardin was the senior vice president of technical operations from April 2015 to October 2016. Prior to that, Mr. DesJardin served as senior vice president of product development at Jazz Pharmaceuticals plc (formerly Jazz Pharmaceuticals, Inc.) from July 2004 to March 2015. Mr. DesJardin spent nine years as an executive director and engineering fellow at ALZA Corporation and spent 15 years at the Dow Chemical Company working in pharmaceutical and agricultural chemical development for Marion Merrill Dow. Mr. DesJardin has over 40 years of experience in pharmaceutical development. Mr. DesJardin received a bachelor of science degree in chemical engineering from the University of California, Berkeley, and is a registered professional engineer in the State of California.

Andy Pasternak. Mr. Pasternak has served as our executive vice president, chief strategy officer since March 2020 and previously served as our executive vice president, chief business officer from November 2019 until March 2020. Prior to joining Horizon, Mr. Pasternak served as a partner of Bain & Company, Inc., a global management consulting firm, from 2008 until October 2019, where he most recently led Bain & Company’s healthcare practice in the Americas and was a member of the mergers and acquisition practice. Mr. Pasternak earned a master of business administration degree from the University of Chicago and a bachelor of arts degree in economics from Northwestern University.

Jeffrey W. Sherman, M.D., FACP. Dr. Sherman has served as our executive vice president, chief medical officer since January 2018. From September 2014 to January 2018, Dr. Sherman served as our executive vice president, research and development and chief medical officer. He joined Horizon in 2009 as our executive vice president, development, manufacturing, regulatory affairs and chief medical officer. Prior to joining Horizon, Dr. Sherman served as president and board member of the Drug Information Association (DIA), a nonprofit professional association of members who work in government regulatory, academia, patient advocacy and the pharmaceutical and medical device industry. Before that he held other management roles at IDM Pharma, Inc., Takeda Global Research & Development, NeoPharm, Inc. and G.D. Searle, LLC/Pharmacia. Dr. Sherman serves on the board of directors of Xeris BioPharma Holdings, Inc., a public biopharmaceutical company (Xeris BioPharma), and previously served on the board of directors of Strongbridge Biopharma plc from October 2016 until October 2021 and Xeris Pharmaceuticals Inc. (Xeris) from April 2018 until October 2021. Xeris acquired Strongbridge in October 2021 and in connection therewith both Xeris and Strongbridge became wholly owned subsidiaries of Xeris BioPharma. He also serves on the board of directors of Sorriso Pharmaceuticals, Inc., a private biotechnology company, the Biotechnology Innovation Organization (BIO) Health Section Governing Board and the board of advisors of the Center for Information and Study on Clinical Research Participation (CISCRP). He is an adjunct assistant professor of Medicine at the Northwestern University Feinberg School of Medicine and a diplomat of the National Board of Medical Examiners and the American Board of Internal Medicine. Dr. Sherman received his medical degree from the Rosalind Franklin University/ Chicago Medical School.

Elizabeth H.Z. Thompson, Ph.D. Dr. Thompson has served as our executive vice president, research and development since March 2021. Previously she served as our group vice president, development and external search from January 2020 to March 2021, and as our vice president, clinical development (rare disease) from June 2018 to January 2020. Prior to joining Horizon, she was with AbbVie as group scientific director, clinical development from April 2017 to May 2018 and senior scientific director, clinical development, from September 2015 to April 2017. While at AbbVie, she was the clinical lead for risankizumab (SKYRIZI), supporting global submissions and approvals. Before AbbVie, Dr. Thompson held roles at Raptor, InterMune and Amgen in a career spanning clinical development, business development and medical communications. Dr. Thompson received a bachelor of science degree in chemistry from Harvey Mudd College and a doctorate in macromolecular and cellular structure and chemistry from The Scripps Research Institute.

COMPENSATION DISCUSSION AND ANALYSIS

This Compensation Discussion and Analysis (CD&A) discusses the compensation philosophy, policies and principles underlying our executive compensation decisions made for the 2022 fiscal year. This CD&A provides qualitative information on the factors relevant to these decisions and the manner in which compensation is awarded to the following executive officers who have been named in the Summary Compensation Table included in this Proxy Statement and whom we refer to as our named executive officers (NEOs). For additional information regarding our 2022 performance highlights and our 2022 executive compensation program, including the effective alignment between executive compensation and our performance, please see “Proposal 3 – Advisory Vote on Executive Compensation.”

CD&A Reference Guide

2022 Performance

We delivered strong corporate performance during 2022. Highlights include:

Net sales and adjusted EBITDA growth percentages represent year-over-year growth over full-year 2021.

Prior TSR results are not intended to forecast or be indicative of possible future performance of our ordinary shares.

Our Pay Program

Our Board has delegated responsibility for creating, reviewing and making recommendations regarding the compensation of our executive officers to the Compensation Committee of the Board (Compensation Committee), which is composed of independent directors under SEC regulations and the Nasdaq Listing Rules. The role of the Compensation Committee is to oversee our compensation and benefit plans and policies, to administer our equity incentive plans and to annually review and approve or make recommendations to our Board.

Say-on-Pay Results and Shareholder Engagement

Our say-on-pay vote held at our 2022 annual meeting of shareholders was supported by 91% of the votes affirmatively cast, excluding abstentions and broker non-votes. While this vote was only advisory, our Compensation Committee interpreted it to be a very positive affirmation from our shareholders that they strongly endorse our historical compensation philosophy, policies and decisions. Accordingly, the Compensation Committee determined to not make any significant changes in how it went about reviewing and setting compensation levels for our executives as a result of the 2022 say-on-pay vote. When determining how

often to hold an advisory vote on executive compensation, the Board recommended and our shareholders agreed upon, an annual vote. In addition to holding an annual advisory vote on executive compensation, we conduct engagement with our shareholders on executive compensation and corporate governance issues. For additional information regarding how shareholder feedback has influenced our executive compensation program over the past several years, please see “Proposal 3 – Advisory Vote on Executive Compensation” below.

Compensation Program and Governance

In 2022, our executive compensation program continued to emphasize three major pay considerations: long-term performance against our business strategies and goals, alignment of the interests of our shareholders, employees and patients, and risk mitigation. Our Compensation Committee is responsible for oversight of our executive compensation program. Highlights of 2022 policies and practices include:

We believe in providing a competitive total compensation package to our executive management team through a combination of base salary, short-term performance-based cash incentives, long-term performance-based equity incentives, and severance and change-in-control benefits. Our executive compensation programs are designed to achieve the following objectives:

Our Compensation Committee believes that our executive compensation program should include short- and long-term performance incentive components, including cash and equity-based compensation, and should reward consistent performance that meets or exceeds expectations. Our Compensation Committee evaluates both performance and compensation to make sure that the total compensation provided to our executive officers remains competitive relative to compensation paid by companies of similar size and stage of development that operate in the biotech industry and appropriately reflects our relative performance and our own strategic objectives.

Our Compensation Committee seeks to ensure that our executive compensation program is properly rewarding and motivating for our executive officers while aligning their goals with our business strategy and the interests of our shareholders. To do this, our Compensation Committee conducts an annual review of the aggregate level of our executive compensation, the mix of elements used to compensate our executive officers and historical compensation levels, including prior equity awards.

When setting executive compensation opportunities, our Compensation Committee considers several factors, including:

Role of Chief Executive Officer in Compensation Decisions

Our chief executive officer (CEO) typically evaluates the performance of other executive officers and other employees, along with the performance of our company as a whole, against pre-established goals, on an annual basis and makes recommendations to the Compensation Committee with respect to annual base salary adjustments, short-term performance-based cash incentives and annual equity grants for the other executives. The Compensation Committee exercises its own independent discretion in approving compensation for all executive officers and assessing corporate performance against the pre-established goals. The CEO is not present during deliberations or voting with respect to his own compensation.

Risk Analysis

The Compensation Committee has reviewed our compensation policies applicable to our executive officers and other employees and believes that our policies do not encourage excessive and unnecessary risk-taking, and that the level of risk that they do encourage is not reasonably likely to have a material adverse effect on us. The design of our compensation policies and programs encourages our executive officers and other employees to remain focused on both our short- and long-term goals. For example, while our short-term incentive plan (our annual bonus plan) measures performance on an annual basis, our long-term incentive equity grants, which consist of time-based equity awards (RSUs) and performance-based equity awards (PSUs) vest over a number of years. Furthermore, our PSUs require that we achieve a specified level of performance over multi-year periods, which we believe encourages our executives and employees to focus on executing our long-term strategy, thus limiting the potential value of excessive risk-taking.

Role of Independent Consultant

Our Compensation Committee retains the services of third-party, independent executive compensation consultants from time to time, as it sees fit, in connection with the establishment of compensation programs and related policies. The Compensation Committee has engaged Aon’s Human Capital Solutions practice, a division of Aon plc (Aon), as its independent consultant since 2016. Total fees paid to Aon in 2022 were approximately $659,000. Aon was engaged to assist and advise on multiple aspects of compensation program design and pay setting, including, but not limited to, the following services:

The Compensation Committee has assessed the independence of Aon under the applicable SEC and Nasdaq standards and concluded that the continued engagement of Aon did not raise any conflict of interest and did not adversely affect Aon’s independence.

Peer Group

Although our Compensation Committee has historically used survey data from Aon as a tool in determining executive compensation, it typically has not used a formula or “benchmark” to set our executives’ compensation in relation to this data. Instead, the Compensation Committee generally references the 50^th percentile of comparable peer companies in combination with multiple other factors, such as the executives’ respective levels of experience, tenure and responsibility in determining the total target compensation for all executives. The peer group used for making 2022 compensation decisions and comparative performance analysis is shown below and was updated by our Compensation Committee in April 2021, with a focus on publicly traded commercial biotech and pharmaceutical companies.

The selection criteria used at the time of the peer group review process were:

Our executive compensation program primarily consists of base salary, annual cash incentives and long-term incentives delivered through equity and cash awards. Employees in more senior roles have an increasing proportion of their total pay package at risk and tied to performance given that their position has greater influence on our operating results.

“Variable” compensation is compensation in which the ultimate value received is contingent either (1) on performance, typically measured as financial, operational, or stock price performance, such as for PSU awards, or (2) on the stock price value at the vesting date, such as for RSU awards.

2022 Pay-for-Performance Overview

A significant portion of total target compensation for our CEO and other NEOs is structured in the form of variable compensation, consisting of annual performance-based incentives and PSUs.

In line with our compensation objectives, including linking executive pay with performance, short-term performance-based incentives and PSUs are dependent on our performance, aligning our executives’ interests with those of our shareholders for short- and long-term performance. In addition, the RSU portion of the total target compensation has a time-based vesting component so that the total potential value realized from the RSU portion is dependent on our long-term share price performance.

Total target compensation for 2022 consisted of annual base salary, target annual bonus and the grant date fair value of PSU and RSU grants. The grant date fair values of PSU and RSU grants were calculated in accordance with the provisions of ASC Topic 718, as reported in the Summary Compensation Table. Approximately 57% of our CEO’s total target compensation for 2022 was tied to the achievement of pre-established performance goals, with time-based equity awards making up approximately 37% of the total. Fixed compensation (annual base salary) made up the remaining 7% of our CEO’s total target compensation.

Base Salary

Base salaries for our executive officers are established based on the individual’s scope of responsibilities, experience and market factors. Base salaries are generally reviewed annually, typically in connection with our annual executive compensation review process. The Compensation Committee references survey and peer group data to understand the marketplace for individuals in similar positions at the peer group companies. Based on the survey and peer group data, the Compensation Committee determined that a 4% increase to the base salaries of our NEOs, with the exceptions of Mr. Walbert, Mr. Hoelscher (who did not receive an increase to his base salary in light of his announced retirement) and Mr. Clayton (who joined us in February 2022), was appropriate and was consistent with industry trends. In considering the 10% increase to Mr. Walbert’s base salary, the Compensation Committee focused on the following items: his tenure and experience as our CEO, his impact and contributions during 2021 and recent market data on CEO compensation at our highest performing peer companies.

The annual base salaries of our NEOs as of March 1, 2022, and the increase from their prior base salary levels, were as follows:

Short-Term Incentive Program: Annual Bonus

We provide performance-based cash annual bonuses as an incentive for our executives to achieve pre-established financial and strategic goals. These bonuses may range in payout from 0% for performance below the threshold level of achievement to 200% of targeted payout levels for performance at or above the maximum level of achievement.

The 2022 target bonus opportunities (expressed as a percentage of base salary paid during the full fiscal year) for our NEOs, which increased by 15 percentage points year-over-year for our CEO and by 10 percentage points year-over-year for our other NEOs (other than Mr. Clayton, who joined us in February 2022), in each case to align their respective target bonus opportunities more closely with market data, were as follows:

In early 2022, the Compensation Committee determined that our annual bonus plan would provide our executives the opportunity to earn performance-based cash awards based on the achievement of a combination of financial goals (60% weighting) and strategic goals (40% weighting).

Financial Goals

The 60% weighting of the financial goals was allocated between a total net sales goal, weighted at 30%, and an internal adjusted earnings before interest, tax, depreciation and amortization (internal adjusted EBITDA) goal, weighted at 30%. We increased the weighting of our internal adjusted EBITDA goal by 5% year-over-year to reflect our heightened focus on margin expansion for 2022.

Total Net Sales

The performance targets for the total net sales goal are set forth below.

Internal Adjusted EBITDA

The performance targets for the internal adjusted EBITDA goal are set forth below:

Strategic Goals

The Compensation Committee established three strategic goals (with a total weighting of 40%) for 2022:

The Compensation Committee chose these three strategic goals because it believed these were the best indicators of the achievement of our operating plan, and they represented the factors most critical to increasing total shareholder value in 2022.

Determination of 2022 Cash Annual Bonus Amounts

In connection with its review of various compensation matters related to the pending acquisition of Horizon by Amgen (referred to herein as the Transaction) announced in December 2022, the Compensation Committee discussed the annual bonus program and considered whether it remained appropriate for payouts to be based solely on achievement of the financial and strategic goals that were established earlier in the year. Specifically, the Compensation Committee considered existing progress towards

achieving the corporate financial and strategic goals described above, as well as the significant shareholder value represented by the Transaction, the fact that management had devoted substantial attention to the process leading to the pending Transaction, the Compensation Committee’s desire for management to focus on the successful closing of the Transaction, and other intervening events that impacted the ability to achieve certain of the previously established corporate goals, including the at-risk launch of a generic version of PENNSAID 2% and our decision to wind down our former inflammation business.

Following this discussion, the Compensation Committee determined that basing annual bonus plan payouts on achievement of the financial and strategic goals established earlier in the year no longer served as the best performance indicator and on-going incentive for our executives and other employees. As a result, and in light of the significant shareholder value represented by the Transaction, the Compensation Committee determined that a payout at the 100% level was appropriate to effectively compensate executives for 2022 performance.

Based on that determination, the Compensation Committee approved cash bonus awards for our NEOs as follows:

In December 2022, in order to eliminate or mitigate the potential tax impact of Sections 280G and 4999 of the Internal Revenue Code of 1986, as amended (the Code), on us and our executive officers with respect to past or future payments to certain executive officers in connection with the Transaction, our Compensation Committee determined that the approved cash bonus awards to Mr. Cox, Mr. Clayton, Dr. Thompson and Mr. Pasternak would be paid on December 30, 2022. The approved cash bonus awards to Mr. Walbert and Mr. Hoelscher were paid on March 15, 2023.

Long-Term Incentive Program

2022 Long-term Incentive Grants

We have adopted a regular, annual long-term incentive grant schedule of awarding equity awards in the form of RSUs and PSUs to our executive officers. In addition, our performance-based equity compensation is aligned with all of our stated compensation objectives, including the linking of executive pay with performance, and aligning the interests of our executive officers and shareholders with a large portion of the equity grants vesting contingent on performance and requiring continued service. Further, we believe that annual grant cycles allow us to more easily manage shareholder dilution and burn rate, while still providing market-competitive incentive opportunities.

As part of our annual long-term incentive plan, on January 4, 2022, we awarded an equal mix of PSUs and time-vested RSUs to our NEOs (other than Mr. Hoelscher, who only received a pro-rated number of time-vested RSUs in light of his announced retirement, and Mr. Clayton, who joined us after the 2022 long-term incentive grants were made). The components of the long-term incentive plan were as follows:

Our NEOs received RSU and PSU grants in January 2022 for the following share amounts:

Time-Vested RSUs

The time-vested RSUs are generally subject to three-year annual vesting over the service period beginning on January 5, 2022 and ending on January 5, 2025.

Pursuant to the agreement we entered into with Mr. Hoelscher in connection with his retirement in May 2022, which is described in the section entitled “Retirement and Transition Agreement with Paul W. Hoelscher” below, Mr. Hoelscher’s time-vested RSUs will continue to vest on their original vesting schedules subject to his continued service as a part-time advisor to us.

Performance-Based PSUs

The performance-based PSUs use three long-term performance metrics: the first component is tied to relative TSR over a three-year period, or Relative TSR PSUs; the second component is tied to the number of pre-established R&D and technical operations goals achieved over a three-year period, or R&D and Technical Operations PSUs; and the third component is tied to the achievement of two financial goals over a two-year period, or Financial PSUs. The Compensation Committee’s decision to include all longer-term (two- or three-year) metrics in the PSU award design was made in line with shareholder feedback.

The performance-based PSUs are determined by the following criteria:

Long-Term Incentive Performance

2022 PSUs

Determination of the attainment level of the Relative TSR PSUs and the attainment level of the R&D and Technical Operations PSUs will be made following the three-year performance period ending December 31, 2024. Determination of the attainment level of the Financial PSUs will be made following the two-year performance period ending December 31, 2023.

2021 R&D and Business Development PSUs

In January 2021, we granted performance-based PSUs tied to the number of pre-established R&D and business development (BD) goals achieved over the two-year period ending December 31, 2022, or R&D/BD PSUs. The number of R&D/BD PSUs that an executive was eligible to earn was based on the number of approved programs (i.e., active clinical-stage development programs, including acquired or in-licensed programs; targeting new indications; new product approvals; or geographical expansions with current or acquired assets) initiated, completed or acquired during the two-year performance period.

In December 2022, the Compensation Committee determined that we exceeded the maximum goal of more than eight approved programs during the two-year performance period. Among the key target programs that the Compensation Committee determined were achieved during the two-year performance period were:

The eligible executives therefore each vested in the number of R&D/BD PSUs set forth in the table below, which represents 200% (the maximum payout percentage) of their target number of R&D/BD PSUs:

2020 Relative TSR PSUs

In January 2020, we granted performance-based PSUs tied to our TSR performance relative to the TSR of the components of the NBI over the three-year performance period ending December 31, 2022. The number of 2020 Relative TSR PSUs that an executive was eligible to earn was determined as follows, with linear interpolation between performance levels: