As filed with the Securities and Exchange Commission on April 28, 2015

Registration No. 333-            

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Viking Therapeutics, Inc.

(Exact name of Registrant as specified in its charter)

Viking Therapeutics, Inc.

11119 North Torrey Pines Road, Suite 50

San Diego, CA 92037

(858) 550-7810

(Address, including zip code, and telephone number, including area code, of Registrant’s principal executive offices)

Brian Lian, Ph.D.

President and Chief Executive Officer

Viking Therapeutics, Inc.

11119 North Torrey Pines Road, Suite 50

San Diego, CA 92037

(858) 550-7810

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Approximate date of commencement of proposed sale to the public: As soon as practicable after this registration statement becomes effective.

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, 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.  x (Registration No. 333-197182)

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 post-effective amendment filed pursuant to Rule 462(d) 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.  ¨

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

CALCULATION OF REGISTRATION FEE

This Registration Statement shall become effective upon filing in accordance with Rule 462(b) under the Securities Act of 1933, as amended.

Explanatory Note and Incorporation By Reference

This Registration Statement on Form S-1 relating to the public offering of common stock of Viking Therapeutics, Inc. contemplated by the Registration Statement on Form S-1 (File No. 333-197182), as amended (the “Prior Registration Statement”), is filed pursuant to Rule 462(b) promulgated under the Securities Act of 1933, as amended, solely to increase the maximum aggregate offering price of the shares be offered in the public offering by $4,600,000, including shares that may be sold pursuant to an option to purchase additional shares granted to the underwriters. The contents of the Prior Registration Statement, including all exhibits thereto, which was declared effective by the Securities and Exchange Commission on April 28, 2015, are hereby incorporated by reference.

The required opinion and consents are listed on the Exhibit Index attached hereto and filed herewith.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, the registrant has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of San Diego, State of California, on April 28, 2015.

Pursuant to the requirements of the Securities Act of 1933, as amended, this registration statement on Form S-1 has been signed by the following persons in the capacities and on the dates indicated.

Exhibit Index