Common Shares

ESSA Pharma Inc.

SUITE 720, Vancouver, British Columbia, A1, 1K5

This statement is filed by: (i) Biotechnology Value Fund, L.P., a Delaware limited partnership ("BVF"); (ii) BVF I GP LLC, a Delaware limited liability company ("BVF GP"), which serves as general partner of BVF; (iii) Biotechnology Value Fund II, L.P., a Delaware limited partnership ("BVF2"); (iv) BVF II GP LLC, a Delaware limited liability company ("BVF2 GP"), which serves as general partner of BVF2; (v) Biotechnology Value Trading Fund OS LP, a Cayman Islands limited partnership ("Trading Fund OS"); (vi) BVF Partners OS Ltd., a Cayman Islands limited liability company ("Partners OS"), which serves as general partner of Trading Fund OS; (vii) BVF GP Holdings LLC, a Delaware limited liability company ("BVF GPH"), which is the sole member of each of BVF GP and BVF2 GP; (viii) BVF Partners L.P., a Delaware limited partnership ("Partners"), which serves as the investment manager of each of BVF, BVF2, Trading Fund OS and a certain managed account (the "Partners Managed Account"), and as the sole member of Partners OS; (ix) BVF Inc., a Delaware corporation, which serves as general partner of Partners and the managing member of BVF GPH; and (x) Mark N. Lampert, who serves as the sole officer and director of BVF Inc. Each of the foregoing is referred to as a "Reporting Person" and collectively as the "Reporting Persons." Each of the Reporting Persons is party to that certain Joint Filing Agreement, as further described in Item 6. Accordingly, the Reporting Persons are hereby filing a joint Schedule 13D.

The business address of BVF, BVF GP, BVF2, BVF2 GP, BVF GPH, Partners, BVF Inc. and Mr. Lampert is 44 Montgomery St., 40th Floor, San Francisco, California 94104. The business address of Trading Fund OS and Partners OS is PO Box 309 Ugland House, Grand Cayman, KY1-1104, Cayman Islands.

The principal business of each of BVF, BVF2 and Trading Fund OS is investing in securities. The principal business of BVF GP, BVF2 GP and Partners OS is serving as the general partner of BVF, BVF2 and Trading Fund OS, respectively. The principal business of BVF GPH is serving as the sole member of each of BVF GP and BVF2 GP. The principal business of Partners is serving as the investment manager of each of BVF, BVF2, Trading Fund OS and the Partners Managed Account, and as the sole member of Partners OS. The principal business of BVF Inc. is serving as the general partner of Partners and as the managing member of BVF GPH. Mr. Lampert is the sole officer and director of BVF Inc.

No Reporting Person has, during the last five years, been party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

Mr. Lampert is a citizen of the United States of America.

The aggregate percentage of Shares reported owned by each person named herein is based on 44,388,550 Shares outstanding as of February 10, 2025, which is the total number of Shares outstanding as reported in the Issuer's Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on February 11, 2025. As of the close of business on April 8, 2025, the Reporting Persons hold 2,920,000 pre-funded warrants, exercisable for an aggregate of 2,920,000 Shares (the "Pre-Funded Warrants"). Each Pre-Funded Warrant entitles the holder thereof to acquire, for a nominal exercise price of $0.0001, one Share. The Pre-Funded Warrants are only exercisable to the extent that the holder, together with its affiliates and any other person or entity acting as a group, would not beneficially own more than 9.99% of the outstanding Shares after giving effect to such exercise, as such percentage ownership is determined in accordance with the terms of the Pre-Funded Warrants (the "Beneficial Ownership Limitation"). As of the close of business on April 8, 2025, the Beneficial Ownership Limitation prohibits the exercise of all of the Pre-Funded Warrants held by the Reporting Persons. As of the date hereof, (i) BVF beneficially owned 4,712,590 Shares, excluding the 1,481,634 Shares issuable upon the exercise of the Pre-Funded Warrants held by it, representing percentage ownership of approximately 10.6% of the Shares outstanding, (ii) BVF2 beneficially owned 3,491,779 Shares, excluding 1,235,030 Shares issuable upon the exercise of the Pre-Funded Warrants held by it, representing percentage ownership of approximately 7.9% of the Shares outstanding, (iii) Trading Fund OS beneficially owned 357,472 Shares, excluding 203,336 Shares issuable upon the exercise of the Pre-Funded Warrants held by it, representing percentage ownership of less than 1% of the Shares outstanding, and (iv) 186,788 Shares were held in the Partners Managed Account, representing percentage ownership of less than 1% of the Shares outstanding. BVF GP, as the general partner of BVF, may be deemed to beneficially own the 4,712,590 Shares beneficially owned by BVF, representing percentage ownership of approximately 10.6% of the Shares outstanding. BVF2 GP, as the general partner of BVF2, may be deemed to beneficially own the 3,491,779 Shares beneficially owned by BVF2, representing percentage ownership of approximately 7.9% of the Shares outstanding. Partners OS, as the general partner of Trading Fund OS, may be deemed to beneficially own the 357,472 Shares beneficially owned by Trading Fund OS, representing percentage ownership of less than 1% of the Shares outstanding. BVF GPH, as the sole member of each of BVF GP and BVF2 GP, may be deemed to beneficially own the 8,204,369 Shares beneficially owned in the aggregate by BVF and BVF2, representing percentage ownership of approximately 18.5% of the Shares outstanding. Partners, as the investment manager of BVF, BVF2, Trading Fund OS and the Partners Managed Account and the sole member of Partners OS, may be deemed to beneficially own the 8,748,629 Shares beneficially owned in the aggregate by BVF, BVF2, Trading Fund OS, and held in the Partners Managed Account, representing percentage ownership of approximately 19.7% of the Shares outstanding. BVF Inc., as the general partner of Partners, may be deemed to beneficially own the 8,748,629 Shares beneficially owned by Partners, representing percentage ownership of approximately 19.7% of the Shares outstanding. Mr. Lampert, as the sole director and officer of BVF Inc., may be deemed to beneficially own the 8,748,629 Shares beneficially owned by BVF Inc., representing percentage ownership of approximately 19.7% of the Shares outstanding. The foregoing should not be construed in and of itself as an admission by any Reporting Person as to beneficial ownership of any Shares owned by another Reporting Person. BVF GP disclaims beneficial ownership of the Shares beneficially owned by BVF. BVF2 GP disclaims beneficial ownership of the Shares beneficially owned by BVF2. Partners OS disclaims beneficial ownership of the Shares beneficially owned by Trading Fund OS. BVF GPH disclaims beneficial ownership of the Shares beneficially owned by BVF and BVF2. Each of Partners, BVF Inc. and Mr. Lampert disclaims beneficial ownership of the Shares beneficially owned by BVF, BVF2 and Trading Fund OS and held in the Partners Managed Account.

Each of BVF, BVF2 and Trading Fund OS shares with Partners voting and dispositive power over the Shares each such entity beneficially owns. BVF shares with BVF GP voting and dispositive power over the Shares beneficially owned by BVF. BVF2 shares with BVF2 GP voting and dispositive power over the Shares beneficially owned by BVF2. Each of BVF GP and BVF2 GP shares with BVF GPH voting and dispositive power over the Shares each such entity beneficially owns. Trading Fund OS shares with Partners OS voting and dispositive power over the Shares beneficially owned by Trading Fund OS. Partners, BVF Inc. and Mr. Lampert share voting and dispositive power over the Shares they may be deemed to beneficially own with BVF, BVF GP, BVF2, BVF2 GP, Trading Fund OS, Partners OS and BVF GPH and held in the Partners Managed Account.

None of the Reporting Persons has entered into any transactions in the Securities of the Issuer during the past 60 days.

No person other than the Reporting Persons is known to have the right to receive, or the power to direct the receipt of dividends from, or proceeds from the sale of, the Shares.

Not applicable.