Schedule 13G: RA Capital Reports 1,675,000 Shares (7.5%) of LB Pharmaceuticals

Rhea-AI Filing Summary

RA Capital and affiliated persons reported ownership of 1,675,000 shares, representing 7.5% of LB PHARMACEUTICALS INC (ticker LBRX) common stock as of September 12, 2025. The holdings are reported across RA Capital Management, L.P., RA Capital Healthcare Fund, L.P., and two individuals, Peter Kolchinsky and Rajeev Shah, each shown with shared voting and dispositive power over the 1,675,000 shares and no sole voting or dispositive power. The filing states the Fund holds the shares directly, RA Capital serves as the Fund’s investment adviser with delegated voting and disposition authority, and the Reporting Persons expressly disclaim that they form a "group." The 7.5% figure is calculated using 22,442,989 shares outstanding disclosed in the issuer’s September 10, 2025 prospectus.

Positive

• Institutional investment disclosed: RA Capital and affiliates report a material 7.5% stake (1,675,000 shares) in LBRX.
• Clear governance disclosure: Delegation of voting and disposition authority and disclaimers regarding group status and beneficial ownership are explicitly stated.
• Calculation basis provided: Percentage ownership is tied to 22,442,989 shares outstanding per the issuer’s prospectus, giving transparency to the percent figure.

Negative

• None.

Insights

Financial Analyst

TL;DR: Institutional stake of 7.5% by RA Capital signals material ownership that investors should note for shareholder composition.

The Schedule 13G shows an institutional investor and affiliated parties hold 1,675,000 shares (7.5%) of LBRX, reported under passive investor rules. The filing clarifies that RA Capital is the adviser to the Fund and has delegated voting and disposition authority, while the Fund disclaims beneficial ownership for Section 13(d) purposes due to delegation terms. The ownership percentage is based on 22,442,989 shares outstanding per the issuer’s prospectus, providing a clear basis for the calculation. No transactions, intent to influence control, or group formation are disclosed.

Corporate Governance Expert

TL;DR: Ownership structure and disclaimers are standard; delegation of voting/dispositive power is explicitly disclosed.

The filing details that the Fund directly holds the reported shares while RA Capital has been delegated voting and disposition authority and that RA Capital, Dr. Kolchinsky, and Mr. Shah disclaim broader beneficial ownership except for Section 13(d) obligations. The Reporting Persons expressly disclaim that they constitute a "group," and Item 10 certification states the holdings were not acquired to change or influence control. The document includes signatures and a joint filing agreement exhibit, meeting formal disclosure requirements.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

LB PHARMACEUTICALS INC

(Name of Issuer)

Common Stock, $0.0001 par value per share

(Title of Class of Securities)

50180M108

(CUSIP Number)

09/12/2025

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

SCHEDULE 13G

CUSIP No. 50180M108

1

Names of Reporting Persons

RA Capital Management, L.P.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 1,675,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 1,675,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,675,000.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

7.5 %

12

Type of Reporting Person (See Instructions)

IA, PN

SCHEDULE 13G

CUSIP No. 50180M108

1

Names of Reporting Persons

Peter Kolchinsky

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 1,675,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 1,675,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,675,000.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

7.5 %

12

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13G

CUSIP No. 50180M108

1

Names of Reporting Persons

Rajeev Shah

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 1,675,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 1,675,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,675,000.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

7.5 %

12

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13G

CUSIP No. 50180M108

1

Names of Reporting Persons

RA Capital Healthcare Fund, L.P.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 1,675,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 1,675,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,675,000.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

7.5 %

12

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13G

Item 1.
(a)	Name of issuer: LB PHARMACEUTICALS INC
(b)	Address of issuer's principal executive offices: One Pennsylvania Plaza, Suite 1025, New York, NY, 10119.
Item 2.
(a)	Name of person filing: The names of the persons filing this report (collectively, the "Reporting Persons") are: RA Capital Management, L.P. ("RA Capital") Peter Kolchinsky ("Dr. Kolchinsky") Rajeev Shah ("Mr. Shah") RA Capital Healthcare Fund, L.P. (the "Fund") The Reporting Persons expressly disclaim status as a "group" for purposes of this Schedule 13G.
(b)	Address or principal business office or, if none, residence: The address of the principal business office of each of the Reporting Persons is: c/o RA Capital Management, L.P., 200 Berkeley Street, 18th Floor, Boston MA 02116
(c)	Citizenship: RA Capital and the Fund are Delaware limited partnerships. Dr. Kolchinsky and Mr. Shah are United States citizens.
(d)	Title of class of securities: Common Stock, $0.0001 par value per share
(e)	CUSIP No.: 50180M108
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: Row 9 of each Reporting Person's cover page to this Schedule 13G sets forth the aggregate number of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference. The Fund directly holds 1,675,000 shares of the Issuer's Common Stock. RA Capital Healthcare Fund GP, LLC is the general partner of the Fund. The general partner of RA Capital is RA Capital Management GP, LLC, of which Dr. Kolchinsky and Mr. Shah are the controlling persons. RA Capital serves as investment adviser for the Fund and may be deemed a beneficial owner, for purposes of Section 13(d) of the Act, of any securities of the Issuer held by the Fund. The Fund has delegated to RA Capital the sole power to vote and the sole power to dispose of all securities held in the Fund's portfolio, including the shares of the Issuer's Common Stock reported herein. Because the Fund has divested voting and investment power over the reported securities it holds and may not revoke that delegation on less than 61 days' notice, the Fund disclaims beneficial ownership of the securities it holds for purposes of Section 13(d) of the Act. As managers of RA Capital, Dr. Kolchinsky and Mr. Shah may be deemed beneficial owners, for purposes of Section 13(d) of the Act, of any securities of the Issuer beneficially owned by RA Capital. RA Capital, Dr. Kolchinsky, and Mr. Shah disclaim beneficial ownership of the securities reported in this Schedule 13G other than for the purpose of determining their obligations under Section 13(d) of the Act, and the filing of this Schedule 13G shall not be deemed an admission that either RA Capital, Dr. Kolchinsky, or Mr. Shah is the beneficial owner of such securities for any other purpose.
(b)	Percent of class: Row 11 of each Reporting Person's cover page to this Schedule 13G sets forth the percentages of shares of Common Stock of the Issuer beneficially owned by such Reporting Person and is incorporated by reference. Such percentage is based upon 22,442,989 shares of Common Stock outstanding as of September 12, 2025, as disclosed in the Issuer's final prospectus dated September 10, 2025 filed with the Securities and Exchange Commission (the "SEC") on September 12, 2025.
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: Row 5 of each Reporting Person's cover page to this Schedule 13G sets forth the sole power to vote or to direct the vote of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
	(ii) Shared power to vote or to direct the vote: Row 6 of each Reporting Person's cover page to this Schedule 13G sets forth the shared power to vote or to direct the vote of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
	(iii) Sole power to dispose or to direct the disposition of: Row 7 of each Reporting Person's cover page to this Schedule 13G sets forth the sole power to dispose or to direct the disposition of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
	(iv) Shared power to dispose or to direct the disposition of: Row 8 of each Reporting Person's cover page to this Schedule 13G sets forth the shared power to dispose or to direct the disposition of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
Item 5.	Ownership of 5 Percent or Less of a Class.
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	Not Applicable
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

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.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

RA Capital Management, L.P.

Signature:	/s/ Peter Kolchinsky
Name/Title:	By Peter Kolchinsky, Authorized Signatory
Date:	09/19/2025

Peter Kolchinsky

Signature:	/s/ Peter Kolchinsky
Name/Title:	Peter Kolchinsky
Date:	09/19/2025

Rajeev Shah

Signature:	/s/ Rajeev Shah
Name/Title:	Rajeev Shah
Date:	09/19/2025

RA Capital Healthcare Fund, L.P.

Signature:	/s/ Peter Kolchinsky
Name/Title:	By RA Capital Healthcare Fund GP, LLC, its General Partner, By Peter Kolchinsky, Manager
Date:	09/19/2025

Exhibit Information

Exhibit 99.1 Joint Filing Agreement

FAQ

How many LBRX shares does RA Capital report owning?

The Reporting Persons collectively report ownership of 1,675,000 shares of LB PHARMACEUTICALS INC common stock.

What percentage of LBRX does the 1,675,000 shares represent?

The filing states this equals 7.5% of the class, based on 22,442,989 shares outstanding from the issuer’s September 10, 2025 prospectus.

Who are the reporting persons in this Schedule 13G for LBRX?

The report lists RA Capital Management, L.P., RA Capital Healthcare Fund, L.P., Peter Kolchinsky, and Rajeev Shah as the Reporting Persons.

Does the filing indicate RA Capital intends to influence control of LB PHARMACEUTICALS INC?

No. Item 10 certification states the securities were not acquired and are not held for the purpose of changing or influencing control, and the filing is made under Schedule 13G (passive reporting).

What voting and dispositive powers are reported for these holdings?

Each Reporting Person reports 0 sole voting power and 1,675,000 shared voting and shared dispositive power, with 0 sole dispositive power.