Sec Form 4 Filing - Vida Ventures GP III, L.L.C. @ LB PHARMACEUTICALS INC - 2025-09-12

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Vida Ventures GP III, L.L.C. 2. Issuer Name and Ticker or Trading Symbol LB PHARMACEUTICALS INC [ LBRX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 10100 SANTA MONICA BOULEVARD, SUITE 1500 3. Date of Earliest Transaction (MM/DD/YY) 09/12/2025 (Street) LOS ANGELES, CA90067 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 09/12/2025 C( 1 ) 547,648 A 547,648 I By Vida Ventures III, L.P. ( 2 ) ( 3 ) Common Stock 09/12/2025 C( 1 ) 1,262 A 1,262 I By Vida Ventures III-A, L.P. ( 4 ) Common Stock 09/12/2025 P 332,566 A $ 15 880,214 I By Vida Ventures III, L.P. ( 2 ) ( 3 ) Common Stock 09/12/2025 P 767 A $ 15 2,029 I By Vida Ventures III-A, L.P. ( 4 ) Common Stock 1,434 I By Vida Ventures Management Co. LLC ( 5 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Series C Preferred Stock ( 1 ) 09/12/2025 C 13,302,666 ( 1 ) ( 1 ) Common Stock 547,648 $ 0 0 I By Vida Ventures III, L.P. ( 2 ) ( 3 ) Series C Preferred Stock ( 1 ) 09/12/2025 C 30,667 ( 1 ) ( 1 ) Common Stock 1,262 $ 0 0 I By Vida Ventures III-A, L.P. ( 4 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Vida Ventures GP III, L.L.C. 10100 SANTA MONICA BOULEVARD SUITE 1500 LOS ANGELES, CA90067 X Vida Ventures III, L.P. 10100 SANTA MONICA BOULEVARD SUITE 1500 LOS ANGELES, CA90067 X Vida Ventures III-A, L.P. 10100 SANTA MONICA BOULEVARD SUITE 1500 LOS ANGELES, CA90067 X Belldegrun Arie 10100 SANTA MONICA BOULEVARD SUITE 1500 LOS ANGELES, CA90067 X Vida Ventures Management Co. LLC 10100 SANTA MONICA BOULEVARD SUITE 1500 LOS ANGELES, CA90067 X Signatures VIDA VENTURES GP III, L.L.C., By: /s/ Jean-Philippe Kouakou-Zebouah, its Managing Member 09/16/2025 Signature of Reporting Person Date VIDA VENTURES III, L.P., By: Vida Ventures GP III, L.L.C., its general partner, By: /s/ Jean-Philippe Kouakou-Zebouah, its Managing Member 09/16/2025 Signature of Reporting Person Date VIDA VENTURES III-A, L.P., By: Vida Ventures GP III, L.L.C., its general partner, By: /s/ Jean-Philippe Kouakou-Zebouah, its Managing Member 09/16/2025 Signature of Reporting Person Date VIDA VENTURES MANAGEMENT CO., LLC, By: /s/ Jean-Philippe Kouakou-Zebouah, its Managing Member 09/16/2025 Signature of Reporting Person Date ARIE BELLDEGRUN By: /s/ Jean-Philippe Kouakou-Zebouah, his attorney-in-fact 09/16/2025 Signature of Reporting Person Date HELEN KIM By: /s/ Jean-Philippe Kouakou-Zebouah, her attorney-in-fact 09/16/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Each share of Series C Preferred Stock has no expiration date and converted automatically into Common Stock immediately prior to the Issuer's initial public offering at a conversion ratio based upon the initial price per share to the public in the Issuer's initial public offering. ( 2 )These shares are held directly by Vida Ventures III, L.P. ("Vida III"). Vida Ventures GP III, L.L.C. ("Vida III GP") is the general partner of Vida III and may be deemed to have voting, investment, and dispositive power with respect to these securities. Arie Belldegrun, Helen Kim and Rajul Jain, are the members of the investment committee of Vida III GP (each, an "Investment Committee Member" and such committee, the "Investment Committee"). ( 3 )(Continued from Footnote 2) The Investment Committee and each of the Investment Committee Members may be deemed to share voting, investment and dispositive power with respect to these securities. Vida III GP, the Investment Committee and each of the Investment Committee Members disclaims beneficial ownership of the securities held of record by Vida III, and this report shall not be deemed an admission that they are the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of their pecuniary interest therein, if any. ( 4 )These shares are held directly by Vida Ventures III-A, L.P. ("Vida III-A"). Vida III GP is the general partner of Vida III-A and may be deemed to have voting, investment, and dispositive power with respect to these securities. The Investment Committee and each of the Investment Committee Members may be deemed to share voting, investment and dispositive power with respect to these securities. Vida III GP, the Investment Committee and each of the Investment Committee Members disclaims beneficial ownership of the securities held of record by Vida III-A, and this report shall not be deemed an admission that they are the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of their pecuniary interest therein, if any. ( 5 )These shares are held directly by Vida Ventures Management Co., LLC ("Vida Management"). Each Investment Committee Member (as defined below) disclaims beneficial ownership of the securities held of record by Vida Management, and this report shall not be deemed an admission that they are the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of their pecuniary interest therein, if any.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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