Xenon Pharmaceuticals Announces Proposed Public Offering

VANCOUVER, British Columbia and BOSTON, MA, March 09, 2026 — Xenon Pharmaceuticals Inc. (Nasdaq: XENE), a neuroscience-focused biopharmaceutical company dedicated to drug discovery, clinical development and commercialization of life-changing therapeutics for patients in need, today announced that it has commenced an underwritten public offering of $500.0 million of its common shares, pursuant to its existing shelf registration statement. All of the common shares in this offering are being offered by Xenon. In addition, Xenon intends to grant the underwriters an option for a period of 30 days to purchase up to an additional $75.0 million of common shares at the public offering price, less the underwriting discounts and commissions. The proposed offering is subject to market and other conditions, and there can be no assurance as to whether or when the offering may be completed.

J.P. Morgan, Jefferies, TD Cowen, Stifel, RBC Capital Markets, and William Blair are acting as joint book-running managers for the proposed offering. Baird is acting as lead manager for the proposed offering.

An automatically effective shelf registration statement relating to the securities offered in the proposed public offering described above was filed with the Securities and Exchange Commission (the “SEC”) on August 9, 2024. The proposed offering will be made only by means of a written prospectus and prospectus supplement that form a part of the registration statement. A preliminary prospectus supplement and accompanying prospectus relating to the proposed offering will be filed with the SEC and will be available on the SEC’s website at www.sec.gov. Copies of the preliminary prospectus supplement and the accompanying prospectus, when available, may also be obtained by contacting J.P. Morgan Securities LLC, c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY 11717 or by email at [email protected] and [email protected]; Jefferies LLC, Attention: Equity Syndicate Prospectus Department, 520 Madison Avenue New York, NY 10022, by telephone at (877) 821-7388, or by email at [email protected]; TD Securities (USA) LLC, c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY 11717 or by email at [email protected]; Stifel, Nicolaus & Company, Incorporated, Attention: Syndicate, One Montgomery Street, Suite 3700, San Francisco, CA 94104, telephone: (415) 364-2720 or by emailing [email protected]; RBC Capital Markets, LLC, Attention: Equity Capital Markets, 200 Vesey Street, New York, NY 10281, by telephone at (877) 822-4089, or by email at [email protected]; or William Blair & Company, L.L.C., Attention: Prospectus Department, 150 North Riverside Plaza, Chicago, Illinois 60606, by telephone at (800) 621-0687 or by email at [email protected].

No securities are being offered or sold, directly or indirectly, in Canada or to any resident of Canada.

This press release shall not constitute an offer to sell or the solicitation of an offer to buy the securities being offered, nor shall there be any sale of the securities being offered in any state or other jurisdiction in which such offer, solicitation or sale would be unlawful prior to the registration or qualification under the securities laws of any such state or other jurisdiction.

About Xenon Pharmaceuticals Inc.

Xenon Pharmaceuticals (Nasdaq: XENE) is a neuroscience-focused biopharmaceutical company dedicated to drug discovery, clinical development and commercialization of life-changing therapeutics for patients in need. Xenon’s lead molecule, azetukalner, is a novel, potent KV7 potassium channel opener in Phase 3 clinical trials for the treatment of epilepsy, major depressive disorder (MDD) and bipolar depression (BPD). Xenon is also advancing an early-stage portfolio of multiple promising potassium and sodium channel modulators, including KV7 and NaV1.7 programs in Phase 1 development for the potential treatment of pain. Xenon has offices in Vancouver, British Columbia, and Boston, Massachusetts.

Xenon and the Xenon logo are registered trademarks or trademarks of Xenon Pharmaceuticals Inc. in the US, Canada, and elsewhere. All other trademarks belong to their respective owner.

Investor Contact: Tucker Kelly Chief Financial Officer Email: [email protected]