SCHEDULE 13D/A 0001193805-25-000447 0000918923 XXXXXXXX LIVE 1 Common Shares 08/05/2025 true 0001633932 29668H708 ESSA Pharma Inc.

SUITE 720 999 WEST BROADWAY VANCOUVER A1 V5Z 1K5

JAMES KRATKY 415-525-8800 BVF PARTNERS L.P. 44 Montgomery St., 40th Floor San Francisco CA 94104 KENNETH A. SCHLESINGER, ESQ. 212-451-2300 OLSHAN FROME WOLOSKY LLP 1325 Avenue of the Americas New York NY 10019 0000918923 N BIOTECHNOLOGY VALUE FUND L P a WC N DE 0.00 6194145.00 0.00 6194145.00 6194145.00 N 13.1 PN 0001803805 N BVF I GP LLC a AF N DE 0.00 6194145.00 0.00 6194145.00 6194145.00 N 13.1 OO 0001102444 N BIOTECHNOLOGY VALUE FUND II LP a WC N DE 0.00 4726743.00 0.00 4726743.00 4726743.00 N 9.99 PN 0001803806 N BVF II GP LLC a AF N DE 0.00 4726743.00 0.00 4726743.00 4726743.00 N 9.99 OO 0001660683 N Biotechnology Value Trading Fund OS LP a WC N E9 0.00 560797.00 0.00 560797.00 560797.00 N 1.2 PN 0001660684 N BVF Partners OS Ltd. a AF N E9 0.00 560797.00 0.00 560797.00 560797.00 N 1.2 CO 0001803809 N BVF GP HOLDINGS LLC a AF N DE 0.00 10920888.00 0.00 10920888.00 10920888.00 N 23.1 OO 0001055947 N BVF PARTNERS L P/IL a AF N DE 0.00 11668473.00 0.00 11668473.00 11668473.00 N 24.7 IA PN 0001056807 N BVF INC/IL a AF N DE 0.00 11668473.00 0.00 11668473.00 11668473.00 N 24.7 CO 0001233840 N LAMPERT MARK N a AF N X1 0.00 11668473.00 0.00 11668473.00 11668473.00 N 24.7 IN Common Shares ESSA Pharma Inc. SUITE 720 999 WEST BROADWAY VANCOUVER A1 V5Z 1K5 Item 3 is hereby amended and restated to read as follows: The securities of the Issuer purchased by each of BVF, BVF2 and Trading Fund OS, and held in the Partners Managed Account, were purchased with working capital (which may, at any given time, include margin loans made by brokerage firms in the ordinary course of business). The aggregate purchase price of the 6,194,145 Common Shares (the "Shares") owned directly by BVF is approximately $22,714,817, including brokerage commissions. The aggregate purchase price of the 4,726,743 Shares owned directly by BVF2 is approximately $16,575,234, including brokerage commissions. The aggregate purchase price of the 560,797 Shares owned directly by Trading Fund OS is approximately $1,779,975, including brokerage commissions. The aggregate purchase price of the 186,788 Shares held in the Partners Managed Account is approximately $1,292,828, including brokerage commissions. Item 4 is hereby amended to add the following: On August 5, 2025, certain of the Reporting Persons including BVF, BVF2 and Trading Fund OS entered into a waiver and agreement to exercise (the "Waiver and Agreement") with the Issuer with respect to the amended and restated common share purchase warrants (the "Pre-Funded Warrants") held by them in connection with the Issuer's proposed upcoming merger. Pursuant to the Waiver and Agreement, (i) BVF, BVF2, Trading Fund OS and the Issuer agreed to waive the 19.99% beneficial ownership limitation set forth in Section 2(e) of the Pre-Funded Warrants to permit the full exercise of the of the Pre-Funded Warrants held by them, and (ii) BVF, BVF2 and Trading Fund OS exercised all of the Pre-Funded Warrants held by them in a cashless exercise to acquire 1,481,555 Shares, 1,234,964 Shares and 203,325 Shares, respectively, effective August 5, 2025 (the "Exercise"). A copy of the Waiver and Agreement is attached hereto as Exhibit 99.1 and is incorporated herein by reference. Item 5(a) is hereby amended and restated to read as follows: The aggregate percentage of Shares reported owned by each person named herein is based upon a denominator that is the sum of (i) 44,388,550 Shares outstanding, which is the total number of Shares expected to be outstanding as of August 5, 2025 as reported in the Issuer's Preliminary Proxy Statement on Schedule 14A filed with the Securities and Exchange Commission on July 30, 2025, and (ii) 2,919,844 Shares acquired by certain of the Reporting Persons in connection with the cashless exercise of the Pre-Funded Warrants described in further detail in Item 4 above. As of the date hereof, (i) BVF beneficially owned 6,194,145 Shares, representing percentage ownership of approximately 13.1% of the Shares outstanding, (ii) BVF2 beneficially owned 4,726,743 Shares, representing percentage ownership of approximately 9.99% of the Shares outstanding, (iii) Trading Fund OS beneficially owned 560,797 Shares, representing percentage ownership of approximately 1.2% 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 6,194,145 Shares beneficially owned by BVF, representing percentage ownership of approximately 13.1% of the Shares outstanding. BVF2 GP, as the general partner of BVF2, may be deemed to beneficially own the 4,726,743 Shares beneficially owned by BVF2, representing percentage ownership of approximately 9.99% of the Shares outstanding. Partners OS, as the general partner of Trading Fund OS, may be deemed to beneficially own the 560,797 Shares beneficially owned by Trading Fund OS, representing percentage ownership of approximately 1.2% 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 10,920,888 Shares beneficially owned in the aggregate by BVF and BVF2, representing percentage ownership of approximately 23.1% 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 11,668,473 Shares beneficially owned in the aggregate by BVF, BVF2, Trading Fund OS, and held in the Partners Managed Account, representing percentage ownership of approximately 24.7% of the Shares outstanding. BVF Inc., as the general partner of Partners, may be deemed to beneficially own the 11,668,473 Shares beneficially owned by Partners, representing percentage ownership of approximately 24.7% of the Shares outstanding. Mr. Lampert, as the sole director and officer of BVF Inc., may be deemed to beneficially own the 11,668,473 Shares beneficially owned by BVF Inc., representing percentage ownership of approximately 24.7% 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. Item 5(c) is hereby amended and restated to read as follows: Other than as set forth in Item 4 above and in the immediately following sentence, there were no transactions in the securities of the Issuer by the Reporting Persons during the past sixty days. In connection with the Exercise, BVF, BVF2 and Trading Fund OS disposed of 70, 66, and 11 Shares to the Issuer, respectively, based on a market price of $1.8779 per Share. Item 6 is hereby amended to add the following: On August 5, 2025, BVF, BVF2 and Trading Fund OS entered into the Waiver and Agreement with the Issuer as described in Item 4 above. A copy of the Waiver and Agreement is attached hereto as Exhibit 99.1 and is incorporated herein by reference. Item 7 is hereby amended to add the following exhibit: 99.1 - Waiver and Agreement, dated August 5, 2025. BIOTECHNOLOGY VALUE FUND L P /s/ Mark N. Lampert 08/07/2025 BVF I GP LLC /s/ Mark N. Lampert 08/07/2025 BIOTECHNOLOGY VALUE FUND II LP /s/ Mark N. Lampert 08/07/2025 BVF II GP LLC /s/ Mark N. Lampert 08/07/2025 Biotechnology Value Trading Fund OS LP /s/ Mark N. Lampert 08/07/2025 BVF Partners OS Ltd. /s/ Mark N. Lampert 08/07/2025 BVF GP HOLDINGS LLC /s/ Mark N. Lampert 08/07/2025 BVF PARTNERS L P/IL /s/ Mark N. Lampert 08/07/2025 BVF INC/IL /s/ Mark N. Lampert 08/07/2025 LAMPERT MARK N /s/ Mark N. Lampert 08/07/2025