Xenon制药美股招股说明书(2026-03-09版)

Common shares We are offering $500.0 million of our common shares. Our common shares are listed on the Nasdaq Global Market under the symbol “XENE.” The last reported saleprice of our common shares on the Nasdaq Global Market on March6, 2026 was $41.94 per share. (1)See “Underwriting” beginning on page S-27 of this prospectus supplement for additional information regarding underwriters’ compensation. We have granted the underwriters an option for a period of 30 days to purchase up to an additional $75.0millionof our common shares. Investing in our common shares involves a high degree of risk. See “Risk factors” beginning onpageS-8 of this prospectus supplement and under similar headings in the documents incorporated byreference into this prospectus supplement and the accompanying prospectus. Neither the Securities and Exchange Commission nor any state securities commission has approved ordisapproved of these securities or determined if this prospectus supplement or the accompanyingprospectus is truthful or complete. Any representation to the contrary is a criminal offense. The underwriters expect to deliver the common shares to purchasers on or about Joint Book-Running Managers J.P.Morgan Jefferies TDCowen Stifel RBCCapitalMarkets WilliamBlair Lead-Manager ,2026 Table of Contents Table of contents Prospectus supplement About this prospectus supplementProspectus supplement summaryThe offeringRisk factorsForward-looking statementsUse of proceedsDividend policyDilutionMaterial income tax considerationsUnderwritingLegal mattersExpertsWhere you can find more informationInformation incorporated by reference Prospectus About this prospectusProspectus summaryRisk factorsSpecial note regarding forward-looking statementsUse of proceedsDividend policyDescription of share capitalDescription of the warrantsDescription of the unitsPlan of distributionMaterial income tax considerations Legal matters Experts Table of Contents About this prospectus supplement This prospectus supplement and the accompanying prospectus form part of an automatic shelf registration statement on Form S-3 (FileNo.333-281451) that we filed with the U.S. Securities and Exchange Commission, or the SEC, on August9, 2024 as a “well-knownseasoned issuer,” as defined in Rule 405 under the Securities Act of 1933, as amended, or the Securities Act, utilizing a “shelf” registrationprocess. Under this shelf registration process, we may, from time to time, sell common shares and other securities. This document is intwo parts. The first part is this prospectus supplement, which describes the specific terms of this offering of our common shares and alsoadds to and updates the information contained in the accompanying prospectus and the documents incorporated by reference into thisprospectus supplement and the accompanying prospectus. The second part is the accompanying prospectus, which provides moregeneral information about us and related matters. Generally, when we refer to this prospectus supplement, we are referring to both partsof this document combined. To the extent there is a conflict between the information contained in this prospectus supplement and theinformation contained in the accompanying prospectus or any document incorporated by reference therein filed with the SEC prior to thedate of this prospectus supplement, you should rely on the information in this prospectus supplement; provided that if any statement inone of these documents is inconsistent with a statement in another document having a later date, for example, a document incorporatedby reference in the accompanying prospectus, the statement in the document having the later date modifies or supersedes the earlierstatement. Neither we nor the underwriters have authorized anyone to provide any information other than that contained or incorporated by referencein this prospectus supplement, the accompanying prospectus or in any free writing prospectus prepared by or on behalf of us or to whichwe have referred you. We and the underwriters take no responsibility for, and can provide no assurance as to the reliability of, any otherinformation that others may give you. This prospectus supplement and the accompanying prospectus or any free writing prospectus do notconstitute an offer to sell, or a solicitation of an offer to purchase, the securities offered by this prospectus supplement and theaccompanying prospectus or any free writing prospectus in any jurisdiction to or from any person to whom or from whom it is unlawful tomake such offer or solicitation of an offer in such jurisdiction. The information contained in this prospectus supplement or theaccompanying prospectus, or incorporated by reference herein or therein or any free writing prospectus is accurate only as of therespective dates thereof, regardless of the time of delivery of this prospectus supplement and the accompanying prospectus or any freewriting prospectus or of any sale of our common shares. It is imp