Company: LBRX
Filing Date: 2025-09-09
Form Type: 8-A12B
Source: 0001193125-25-198793
Chunk: 1

Company: LB PHARMACEUTICALS INC
Filing Date: 2025-09-09
Form: 8-A12B
Chunk 1
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 Registrant with the Commission pursuant to Rule 424(b) under the Securities Act of 1933, as amended, that
constitutes part of the Registration Statement shall be deemed to be incorporated herein by reference.

Item 2. Exhibits.

Under the “Instructions as to Exhibits” with respect to Form 8-A, no exhibits are required
to be filed with this registration statement because no other securities of the Registrant are registered on The Nasdaq Stock Market LLC and the securities registered hereby are not being registered pursuant to Section 12(g) of the Securities
Exchange Act of 1934, as amended.

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SIGNATURE Pursuant to the requirements of Section 12 of the Securities Exchange Act of 1934, as amended, the Registrant has duly caused this registration statement to be signed on its behalf by the undersigned, thereto duly authorized.

| Date: September 9, 2025 |     | LB PHARMACEUTICALS INC 
 By:                    |     | /s/ Heather Turner             |
|:------------------------|:----|:-----------------------|:----|:-------------------------------|
|                         |     |                        |     | Heather Turner Chief Executive 
 Officer                        |

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