Form POSASR CATALYST PHARMACEUTICALS

As filed with the Securities and Exchange Commission on July 15, 2026

Registration No. 333-274427

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

POST-EFFECTIVE AMENDMENT NO. 2 TO

FORM S-3 REGISTATION STATEMENT

(REGISTRATION NO. 333-274427)

UNDER

THE SECURITIES ACT OF 1933

CATALYST PHARMACEUTICALS, INC.

(Exact name of registrant as specified in its charter)

Richard J. Daly

355 Alhambra Circle

Suite 801

Coral Gables, Florida 33134

(Name and address of agent for service)

(305) 420-3200

(Telephone number, including area code, of agent for service)

With a copy to:

Peter Cohen-Millstein, Esq.

Hogan Lovells Cadwalader US LLP

390 Madison Avenue

New York, New York 10017

(212) 918-3000

Approximate date of commencement of proposed sale to the public: Not applicable.

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box. ☐

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box. ☐

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box. ☒

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box. ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

DEREGISTRATION OF SECURITIES

This Post-Effective Amendment No. 2 (this “Post-Effective Amendment”) relates to the Registration Statement on Form S-3 ASR (Registration No. 333-274427), filed by the Registrant with the Securities and Exchange Commission on September 8, 2023, and as amended on May 31, 2024 (as so amended, the “Registration Statement”), to deregister all securities registered pursuant to the Registration Statement that remain unsold as of the date this Post-Effective Amendment is filed.

On July 15, 2026, pursuant to the terms of an Agreement and Plan of Merger, dated as of May 6, 2026 (the “Merger Agreement”), by and among the Registrant, Angelini Pharma S.p.A., an Italian Società per azioni (“Parent”), and Angelini Cielo Inc., a Delaware corporation and wholly owned subsidiary of Parent (“Merger Sub”), Merger Sub merged with and into the Registrant, with the Registrant surviving the merger as a wholly owned subsidiary of Parent (the “Merger”).

As a result of the Merger, the offerings of the Registrant’s securities pursuant to the above-referenced Registration Statement have been terminated. In compliance with the undertaking contained in the Registration Statement pursuant to Item 512(a)(3) of Regulation S-K, the registrant is filing this Post-Effective Amendment to remove from registration, by means of a post-effective amendment, any of the registered securities which remain unsold under the Registration Statement as of the date of this Post-Effective Amendment.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, the Registrant certifies that it has reasonable grounds to believe that it meets all the requirements for filing on Form S-3 and has duly caused this Post-Effective Amendment to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Coral Gables, State of Florida, on July 15, 2026.

No other person is required to sign this Post-Effective Amendment in reliance upon Rule 478 under the Securities Act of 1933, as amended.