SCHEDULE 13G/A 0001103804 XXXXXXXX LIVE 4 Common Stock, $0.001 par value per share 06/30/2025 0001563880 Trevi Therapeutics, Inc. 89532M101 195 Church Street 16th Floor New Haven CT 06510 Rule 13d-1(c) VIKING GLOBAL INVESTORS LP b DE 0 7505694 0 7505694 7505694 N 5.9 PN See Item 4 Viking Global Opportunities Parent GP LLC b DE 0 7505694 0 7505694 7505694 N 5.9 OO See Item 4 Viking Global Opportunities GP LLC b DE 0 5028815 0 5028815 5028815 N 3.9 OO See Item 4 Viking Global Opportunities Portfolio GP LLC b DE 0 5028815 0 5028815 5028815 N 3.9 OO See Item 4 Viking Global Opportunities Illiquid Investments Sub-Master LP b E9 0 5028815 0 5028815 5028815 N 3.9 PN See Item 4 Viking Global Opportunities Drawdown GP LLC b DE 0 2476879 0 2476879 2476879 N 1.9 OO See Item 4 Viking Global Opportunities Drawdown Portfolio GP LLC b DE 0 2476879 0 2476879 2476879 N 1.9 OO See Item 4 Viking Global Opportunities Drawdown (Aggregator) LP b E9 0 2476879 0 2476879 2476879 N 1.9 PN See Item 4 HALVORSEN OLE ANDREAS b Q8 0 7505694 0 7505694 7505694 N 5.9 IN See Item 4 Ott David C. b X1 0 7505694 0 7505694 7505694 N 5.9 IN See Item 4 Shabet Rose Sharon b X1 0 7505694 0 7505694 7505694 N 5.9 IN See Item 4 Trevi Therapeutics, Inc. 195 Church Street, 16th Floor, New Haven, Connecticut, 06510 Viking Global Investors LP ("VGI"), Viking Global Opportunities Parent GP LLC ("Opportunities Parent"), Viking Global Opportunities GP LLC ("Opportunities GP"), Viking Global Opportunities Portfolio GP LLC ("Opportunities Portfolio GP"), Viking Global Opportunities Illiquid Investments Sub-Master LP ("VGOP"), Viking Global Opportunities Drawdown GP LLC ("VGOD GP"), Viking Global Opportunities Drawdown Portfolio GP LLC ("VGOD Portfolio GP"), Viking Global Opportunities Drawdown (Aggregator) LP ("VGOD"), O. Andreas Halvorsen, David C. Ott and Rose S. Shabet (collectively, the "Reporting Persons") The business address of each of the Reporting Persons is: 600 Washington Boulevard, Floor 11, Stamford, Connecticut 06901. VGI is a Delaware limited partnership; Opportunities Parent, Opportunities GP, Opportunities Portfolio GP, VGOD GP and VGOD Portfolio GP are Delaware limited liability companies; VGOP and VGOD are Cayman Islands exempted limited partnerships; O. Andreas Halvorsen is a citizen of Norway; and David C. Ott and Rose S. Shabet are citizens of the United States. Y This Statement on Schedule 13G relates to shares of Common Stock and pre-funded warrants to purchase shares of Common Stock with an exercise price of $0.001 per share (the "Warrants") held directly by VGOP and VGOD. VGI: 7,505,694 VGI provides managerial services to VGOP and VGOD. VGI has the authority to dispose of and vote the shares of Common Stock that VGOP and VGOD directly own or have the right to purchase upon exercise of the Warrants. VGI does not directly own any shares of Common Stock or Warrants. Based on Rule 13d-3 under the Securities Exchange Act of 1934, as amended (the "Act"), VGI may be deemed to beneficially own the shares of Common Stock that VGOP and VGOD directly own or have the right to purchase upon exercise of the Warrants. VGI beneficially owns 7,505,694 shares of Common Stock consisting of (i) 1,033,810 and 509,190 shares of Common Stock directly owned by VGOP and VGOD, respectively, and (ii) 3,995,005 and 1,967,689 shares of Common Stock beneficially owned by VGOP and VGOD, respectively, which VGOP and VGOD have the right to purchase upon exercise of the Warrants. Opportunities Parent: 7,505,694 Opportunities Parent is the sole member of Opportunities GP, which has the authority to dispose of and vote the shares of Common Stock controlled by Opportunities Portfolio GP (which consists of the shares of Common Stock that VGOP directly owns or has the right to purchase upon exercise of the Warrants), and is the sole member of VGOD GP, which has the authority to dispose of and vote the shares of Common Stock controlled by VGOD Portfolio GP (which consists of the shares of Common Stock that VGOD directly owns or has the right to purchase upon exercise of the Warrants). Opportunities Parent does not directly own any shares of Common Stock or Warrants. Based on Rule 13d-3 under the Act, Opportunities Parent may be deemed to beneficially own the shares of Common Stock that VGOP and VGOD directly own or have the right to purchase upon exercise of the Warrants. Opportunities Parent beneficially owns 7,505,694 shares of Common Stock consisting of (i) 1,033,810 and 509,190 shares of Common Stock directly owned by VGOP and VGOD, respectively, and (ii) 3,995,005 and 1,967,689 shares of Common Stock beneficially owned by VGOP and VGOD, respectively, which VGOP and VGOD have the right to purchase upon exercise of the Warrants. Opportunities GP: 5,028,815 Opportunities GP serves as the sole member of Opportunities Portfolio GP and has the authority to dispose of and vote the shares of Common Stock controlled by Opportunities Portfolio GP, which consists of the shares of Common Stock that VGOP directly owns or has the right to purchase upon exercise of the Warrants. In addition, Opportunities GP is the general partner of each of Viking Global Opportunities Intermediate LP, Viking Global Opportunities III LP, and Viking Global Opportunities LP. Opportunities GP does not directly own any shares of Common Stock or Warrants. Based on Rule 13d-3 under the Act, Opportunities GP may be deemed to beneficially own the shares of Common Stock that VGOP directly owns or has the right to purchase upon exercise of the Warrants. Opportunities GP beneficially owns 5,028,815 shares of Common Stock consisting of 1,033,810 shares of Common Stock directly owned by VGOP and 3,995,005 shares of Common Stock beneficially owned by VGOP, which VGOP has the right to purchase upon exercise of the Warrants. Opportunities Portfolio GP: 5,028,815 Opportunities Portfolio GP serves as the general partner of VGOP and has the authority to dispose of and vote the shares of Common Stock that VGOP directly owns or has the right to purchase upon exercise of the Warrants. Opportunities Portfolio GP does not directly own any shares of Common Stock or Warrants. Based on Rule 13d-3 under the Act, Opportunities Portfolio GP may be deemed to beneficially own the shares of Common Stock that VGOP directly owns or has the right to purchase upon exercise of the Warrants. Opportunities Portfolio GP beneficially owns 5,028,815 shares of Common Stock consisting of 1,033,810 shares of Common Stock directly owned by VGOP and 3,995,005 shares of Common Stock beneficially owned by VGOP, which VGOP has the right to purchase upon exercise of the Warrants. VGOP: 5,028,815 VGOP has the authority to dispose of and vote the 1,033,810 shares of Common Stock that it owns and the 3,995,005 shares of Common Stock it has the right to purchase upon exercise of the Warrants directly owned by it, which power may be exercised by its general partner, Opportunities Portfolio GP, and by VGI, an affiliate of Opportunities Portfolio GP, which provides managerial services to VGOP. Viking Global Opportunities LP (a Delaware limited partnership) and Viking Global Opportunities III LP (a Cayman Islands exempted limited partnership), through its investment in Viking Global Opportunities Intermediate LP (a Cayman Islands exempted limited partnership), invest substantially all of their assets in Viking Global Opportunities Master LP (a Cayman Islands exempted limited partnership), which in turn invests through VGOP. VGOD GP: 2,476,879 VGOD GP serves as the sole member of VGOD Portfolio GP and has the authority to dispose of and vote the shares of Common Stock controlled by VGOD Portfolio GP, which consists of the shares of Common Stock that VGOD directly owns or has the right to purchase upon exercise of the Warrants. In addition, VGOD GP is the general partner of each of Viking Global Opportunities Drawdown (Internal) LP, Viking Global Opportunities Drawdown (Onshore) LP, and Viking Global Opportunities Drawdown (Offshore) LP. VGOD GP does not directly own any shares of Common Stock or Warrants. Based on Rule 13d-3 under the Act, VGOD GP may be deemed to beneficially own the shares of Common Stock that VGOD directly owns or has the right to purchase upon exercise of the Warrants. VGOD GP beneficially owns 2,476,879 shares of Common Stock consisting of 509,190 shares of Common Stock directly owned by VGOD and 1,967,689 shares of Common Stock beneficially owned by VGOD, which VGOD has the right to purchase upon exercise of the Warrants. VGOD Portfolio GP: 2,476,879 VGOD Portfolio GP serves as the general partner of VGOD and has the authority to dispose of and vote the shares of Common Stock that VGOD directly owns or has the right to purchase upon exercise of the Warrants. VGOD Portfolio GP does not directly own any shares of Common Stock or Warrants. Based on Rule 13d-3 under the Act, VGOD Portfolio GP may be deemed to beneficially own the shares of Common Stock that VGOD directly owns or has the right to purchase upon exercise of the Warrants. VGOD Portfolio GP beneficially owns 2,476,879 shares of Common Stock consisting of 509,190 shares of Common Stock directly owned by VGOD and 1,967,689 shares of Common Stock beneficially owned by VGOD, which VGOD has the right to purchase upon exercise of the Warrants. VGOD: 2,476,879 VGOD has the authority to dispose of and vote the 509,190 shares of Common Stock that it directly owns and the 1,967,689 shares of Common Stock it has the right to purchase upon exercise of the Warrants directly owned by it, which power may be exercised by VGOD Portfolio GP, and by VGI, an affiliate of VGOD Portfolio GP, which provides managerial services to VGOD. Viking Global Opportunities Drawdown (Offshore) LP (a Cayman Islands exempted limited partnership) and Viking Global Opportunities Drawdown (Internal) LP (a Delaware limited partnership), through its investment in Viking Global Opportunities Drawdown (Onshore) LP (a Delaware limited partnership), invest substantially all of their assets in VGOD. O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 7,505,694 Mr. Halvorsen, Mr. Ott and Ms. Shabet, as Executive Committee Members of Viking Global Partners LLC (general partner of VGI) and Opportunities Parent, have shared authority to dispose of and vote the shares of Common Stock beneficially owned by VGI and Opportunities Parent. None of Mr. Halvorsen, Mr. Ott and Ms. Shabet directly owns any shares of Common Stock or Warrants. Based on Rule 13d-3 under the Act, each may be deemed to beneficially own the shares of Common Stock that VGOP and VGOD directly own or have the right to purchase upon exercise of the Warrants. Each of Mr. Halvorsen, Mr. Ott and Ms. Shabet beneficially owns 7,505,694 shares of Common Stock consisting of (i) 1,033,810 and 509,190 shares of Common Stock directly owned by VGOP and VGOD, respectively, and (ii) 3,995,005 and 1,967,689 shares of Common Stock beneficially owned by VGOP and VGOD, respectively, which VGOP and VGOD have the right to purchase upon exercise of the Warrants. The percentages set forth herein are based on (i) 121,775,753 shares of Common Stock outstanding as of June 30, 2025, as reported in the Issuer's quarterly report on Form 10-Q, filed with the Securities and Exchange Commission (the "Commission") on August 7, 2025, and (ii) 5,962,694 shares of Common Stock that the Reporting Persons currently have the right to purchase upon exercise of the Warrants. VGI: 5.9% Opportunities Parent: 5.9% Opportunities GP: 3.9% Opportunities Portfolio GP: 3.9% VGOP: 3.9% VGOD GP: 1.9% VGOD Portfolio GP: 1.9% VGOD: 1.9% O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 5.9% VGI: 0 Opportunities Parent: 0 Opportunities GP: 0 Opportunities Portfolio GP: 0 VGOP: 0 VGOD GP: 0 VGOD Portfolio GP: 0 VGOD: 0 O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 0 VGI: 7,505,694 Opportunities Parent: 7,505,694 Opportunities GP: 5,028,815 Opportunities Portfolio GP: 5,028,815 VGOP: 5,028,815 VGOD GP: 2,476,879 VGOD Portfolio GP: 2,476,879 VGOD: 2,476,879 O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 7,505,694 VGI: 0 Opportunities Parent: 0 Opportunities GP: 0 Opportunities Portfolio GP: 0 VGOP: 0 VGOD GP: 0 VGOD Portfolio GP: 0 VGOD: 0 O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 0 VGI: 7,505,694 Opportunities Parent: 7,505,694 Opportunities GP: 5,028,815 Opportunities Portfolio GP: 5,028,815 VGOP: 5,028,815 VGOD GP: 2,476,879 VGOD Portfolio GP: 2,476,879 VGOD: 2,476,879 O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 7,505,694 Y N The response to Item 4 is incorporated by reference herein. Y Y Y N By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11. EXHIBIT A - JOINT FILING AGREEMENT VIKING GLOBAL INVESTORS LP /s/ Scott M. Hendler 08/14/2025 Viking Global Opportunities Parent GP LLC /s/ Scott M. Hendler 08/14/2025 Viking Global Opportunities GP LLC /s/ Scott M. Hendler 08/14/2025 Viking Global Opportunities Portfolio GP LLC /s/ Scott M. Hendler 08/14/2025 Viking Global Opportunities Illiquid Investments Sub-Master LP /s/ Scott M. Hendler 08/14/2025 Viking Global Opportunities Drawdown GP LLC /s/ Scott M. Hendler 08/14/2025 Viking Global Opportunities Drawdown Portfolio GP LLC /s/ Scott M. Hendler 08/14/2025 Viking Global Opportunities Drawdown (Aggregator) LP /s/ Scott M. Hendler 08/14/2025 HALVORSEN OLE ANDREAS /s/ Scott M. Hendler 08/14/2025 Ott David C. /s/ Scott M. Hendler 08/14/2025 Shabet Rose Sharon /s/ Scott M. Hendler 08/14/2025 (1) Scott M. Hendler is signing on behalf of O. Andreas Halvorsen, individually and as an Executive Committee Member of VIKING GLOBAL PARTNERS LLC, on behalf of VIKING GLOBAL INVESTORS LP, and as an Executive Committee Member of VIKING GLOBAL OPPORTUNITIES PARENT GP LLC, on behalf of itself and VIKING GLOBAL OPPORTUNITIES GP LLC, VIKING GLOBAL OPPORTUNITIES PORTFOLIO GP LLC, VIKING GLOBAL OPPORTUNITIES ILLIQUID INVESTMENTS SUB-MASTER LP, VIKING GLOBAL OPPORTUNITIES DRAWDOWN GP LLC, VIKING GLOBAL OPPORTUNITIES DRAWDOWN PORTFOLIO GP LLC and VIKING GLOBAL OPPORTUNITIES DRAWDOWN (AGGREGATOR) LP, pursuant to an authorization and designation letter dated February 9, 2021, which was previously filed with the Commission as an exhibit to a Form 13G filed by Mr. Halvorsen on February 12, 2021 (SEC File No. 005-49737). (2) Scott M. Hendler is signing on behalf of David C. Ott, individually and as an Executive Committee Member of VIKING GLOBAL PARTNERS LLC, on behalf of VIKING GLOBAL INVESTORS LP, and as an Executive Committee Member of VIKING GLOBAL OPPORTUNITIES PARENT GP LLC, on behalf of itself and VIKING GLOBAL OPPORTUNITIES GP LLC, VIKING GLOBAL OPPORTUNITIES PORTFOLIO GP LLC, VIKING GLOBAL OPPORTUNITIES ILLIQUID INVESTMENTS SUB-MASTER LP, VIKING GLOBAL OPPORTUNITIES DRAWDOWN GP LLC, VIKING GLOBAL OPPORTUNITIES DRAWDOWN PORTFOLIO GP LLC and VIKING GLOBAL OPPORTUNITIES DRAWDOWN (AGGREGATOR) LP, pursuant to an authorization and designation letter dated February 9, 2021, which was previously filed with the Commission as an exhibit to a Form 13G filed by Mr. Halvorsen on February 12, 2021 (SEC File No. 005-49737). (3) Scott M. Hendler is signing on behalf of Rose S. Shabet, individually and as an Executive Committee Member of VIKING GLOBAL PARTNERS LLC, on behalf of VIKING GLOBAL INVESTORS LP, and as an Executive Committee Member of VIKING GLOBAL OPPORTUNITIES PARENT GP LLC, on behalf of itself and VIKING GLOBAL OPPORTUNITIES GP LLC, VIKING GLOBAL OPPORTUNITIES PORTFOLIO GP LLC, VIKING GLOBAL OPPORTUNITIES ILLIQUID INVESTMENTS SUB-MASTER LP, VIKING GLOBAL OPPORTUNITIES DRAWDOWN GP LLC, VIKING GLOBAL OPPORTUNITIES DRAWDOWN PORTFOLIO GP LLC and VIKING GLOBAL OPPORTUNITIES DRAWDOWN (AGGREGATOR) LP, pursuant to an authorization and designation letter dated February 9, 2021, which was previously filed with the Commission as an exhibit to a Form 13G filed by Mr. Halvorsen on February 12, 2021 (SEC File No. 005-49737).