GRI Bio, Inc.

As filed with the Securities and Exchange Commission on December 8, 2025.

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

GRI BIO, INC.

(Exact name of registrant as specified in its charter)

2223 Avenida de la Playa, #208

La Jolla, CA 92037

(619)400-1170

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

W. Marc Hertz, Ph.D.

President and Chief Executive Officer

2223 Avenida de la Playa, #208

La Jolla, CA 92037

(619) 400-1170

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

Approximate date of commencement of proposed sale to the public:

As soon as practicable after the effective date of this Registration Statement.

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 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, 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 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, a smaller reporting company or an 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. o

The registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until this Registration Statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

The information in this preliminary prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This preliminary prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

Subject to Completion, dated December 8, 2025

PRELIMINARY PROSPECTUS

Up to 5,128,205 Shares of Common Stock and accompanying 5,128,205 Series F Warrants to Purchase Up to 5,128,205 Shares of Common Stock

or

Up to 5,128,205 Pre-Funded Warrants to Purchase Up to 5,128,205 Shares of Common Stock and accompanying 5,128,205 Series F Warrants to Purchase Up to 5,128,205 Shares of Common Stock

Up to 358,974 Placement Agent Warrants to Purchase Up to 358,974 Shares of Common Stock

Up to 10,615,384 Shares of Common Stock Issuable Upon Exercise of the Series F Warrants, Pre-Funded Warrants and Placement Agent Warrants

We are offering up to 5,128,205 shares of common stock, par value $0.0001 per share (the “Common Stock”), together with up to 5,128,205 Series F warrants to purchase up to 5,128,205 shares of Common Stock (the “Series F Warrants”) pursuant to this prospectus. The assumed combined public offering price for each share of Common Stock, together with the accompanying Series F Warrant, is $1.95, which is equal to the last reported sale price of our Common Stock on The Nasdaq Capital Market on December 2, 2025. The shares of Common Stock and Series F Warrants will be separately issued. For each share of Common Stock issued, the purchaser will receive one Series F Warrant to purchase one share of Common Stock. Each Series F Warrant will have an exercise price of $1.95 per share and will be exercisable beginning on the effective date of stockholder approval of the issuance of the shares upon exercise of the Series F Warrant (the “Warrant Stockholder Approval”), provided however, if the Pricing Conditions (as defined below) are met, the Warrant Stockholder Approval will not be required and the Series F Warrants will be exercisable upon issuance (the “Initial Issuance Date”). The Series F Warrants will expire on the five-year anniversary of the Initial Issuance Date or the effective date of the Warrant Stockholder Approval, as applicable. As used herein “Pricing Conditions” means that the combined public offering price per share and accompanying Series F Warrant is such that the Warrant Stockholder Approval is not required under the rules of The Nasdaq Stock Market LLC (“Nasdaq”) because either (i) the offering is an at-the-market offering under Nasdaq rules and such price equals or exceeds the sum of (a) the applicable “Minimum Price” per share under Nasdaq Rule 5635(d) plus (b) $0.125 per whole share of Common Stock underlying the Series F Warrants or (ii) the offering is a discounted offering where the pricing and discount (including attributing a value of $0.125 per whole share of Common Stock underlying the Series F Warrants) meet the pricing requirements under Nasdaq’s rules.

We are also offering up to 5,128,205 pre-funded warrants (the “Pre-Funded Warrants”) to those purchasers whose purchase of shares of Common Stock in this offering would result in the purchaser, together with its affiliates and certain related parties, beneficially owning more than 4.99% (or, at the election of the purchaser, 9.99%) of our outstanding Common Stock following the consummation of this offering in lieu of the shares of our Common Stock that would result in ownership in excess of 4.99% (or, at the election of the purchaser, 9.99%). Each Pre-Funded Warrant will be exercisable for one share of Common Stock at an exercise price of $0.0001 per share. Each Pre-Funded Warrant is being issued together with the same Series F Warrant described above being issued with each share of Common Stock. The assumed combined public offering price for each such Pre-Funded Warrant, together with the accompanying Series F Warrant to purchase shares of Common Stock, is $1.9499, which is equal to the last reported sale price of our Common Stock on The Nasdaq Capital Market on December 2, 2025, minus $0.0001, the exercise price of the Pre-Funded Warrants. Each Pre-Funded Warrant will be exercisable upon issuance and may be exercised at any time until all of the Pre-Funded Warrants are exercised in full. The Pre-Funded Warrants and accompanying Series F Warrants are immediately separable and will be issued separately in this offering. For each Pre-Funded Warrant issued, the purchaser will receive one Series F Warrant to purchase one share of Common Stock. This prospectus also relates to the offering of the shares of Common Stock issuable upon exercise of the Series F Warrants, Pre-Funded Warrants and Placement Agent Warrants (as defined herein). For each Pre-Funded Warrant sold, the number of shares of Common Stock sold will be reduced on a one-for-one basis.

There is no established public trading market for the Series F Warrants or the Pre-Funded Warrants, and we do not expect a market to develop. We do not intend to apply for listing of the Series F Warrants or the Pre-Funded Warrants on any securities exchange or any other nationally recognized trading system. Without an active trading market, the liquidity of the Series F Warrants and the Pre-Funded Warrants will be limited.

This offering will terminate on December 31, 2025 unless we decide to terminate the offering (which we may do at any time in our discretion) prior to that date. We will have one closing for all the securities purchased in this offering. The combined public offering price per share of Common Stock (or Pre-Funded Warrant in lieu thereof) and accompanying Series F Warrant will be fixed for the duration of this offering.

We have engaged H.C. Wainwright & Co., LLC (the “Placement Agent” or “Wainwright”) to act as our exclusive placement agent in connection with this offering. The Placement Agent has agreed to use its reasonable best efforts to arrange for the sale of the securities offered by this prospectus. The Placement Agent is not purchasing or selling any of the securities we are offering, and the Placement Agent is not required to arrange the purchase or sale of any specific number of securities or dollar amount. We have agreed to pay to the Placement Agent the Placement Agent fees set forth in the table below, which assumes that we sell all of the securities offered by this prospectus. Since we will deliver the securities to be issued in this offering upon our receipt of investor funds, there is no arrangement for funds to be received in escrow, trust or similar arrangement. There is no minimum number of securities or amount of proceeds required as a condition to closing in this offering. In addition, because there is no escrow trust or similar arrangement and no minimum offering amount, investors could be in a position where they have invested in our company, but we are unable to fulfill all of our contemplated objectives due to a lack of interest in this offering. Investors in this offering will not receive a refund in the event that we do not sell an amount of securities sufficient to pursue our business goals described in this prospectus. Further, any proceeds from the sale of securities offered by us will be available for our immediate use, despite uncertainty about whether we would be able to use such funds to effectively implement our business plan. We will bear all costs associated with the offering. See“Plan of Distribution” on page 142 of this prospectus for more information regarding these arrangements.

Our Common Stock is listed on The Nasdaq Capital Market under the symbol “GRI”. On December 2, 2025, the last reported sale price of our Common Stock on The Nasdaq Capital Market was $1.95 per share.

The assumed combined offering price used throughout this prospectus has been included for illustration purposes only, and may not be indicative of the final offering price. The actual combined public offering price per share of Common Stock and accompanying Series F Warrant and the combined public offering price per Pre-Funded Warrant and accompanying Series F Warrant we are offering and the exercise price and other terms of the Series F Warrants will be negotiated between us and the purchasers, in consultation with the Placement Agent based on the trading of our Common Stock prior to this offering, among other factors. Other factors considered in determining the offering price of the securities we are offering and the exercise price and other terms of the Series F Warrants include the history and prospects of our company, the stage of development of our business, our business plans for the future and the extent to which they have been implemented, an assessment of our management, general conditions of the securities markets at the time of the offering and such other factors as were deemed relevant. The combined public offering price per share of Common Stock and accompanying Series F Warrant and the combined public offering price per Pre-Funded Warrant and accompanying Series F Warrant may be at a discount to the current market price of our Common Stock. Therefore, the recent market price used throughout this prospectus may differ substantially from the combined public offering price.

You should read this prospectus, together with additional information described under the heading “Where You Can Find More Information” carefully before you invest in any of our securities.

On February 21, 2025, we effected a reverse stock split of our Common Stock at a ratio of one-for-17 (the “February 2025 Reverse Stock Split”). Unless otherwise indicated, all financial information, share numbers, option numbers, warrant numbers, other derivative security numbers and exercise prices appearing in this prospectus have been adjusted to give effect to the February 2025 Reverse Stock Split.

We are an “emerging growth company” and a “smaller reporting company” under the federal securities laws and are subject to reduced public company disclosure standards. See “Prospectus Summary—Implications of Beinga Smaller Reporting Company” and “Prospectus Summary—Implications of Being an Emerging Growth Company”

Investing in our securities involves risks. Prior to making an investment decision, you should carefully consider all of the information in this prospectus and, in particular, you should evaluate the risk factors set forth under the caption “Risk Factors” beginning on page 10 of this prospectus.

(1)Represents a cash fee equal to 7.0% of the aggregate gross proceeds raised in this offering. In addition, we have also agreed to pay the Placement Agent a management fee equal to 1.0% of the aggregate gross proceeds raised in this offering and to reimburse the Placement Agent for its non-accountable expenses in the amount of $25,000 , for its legal fees and expenses and other out-of-pocket expenses in an amount of up to $100,000 and for its clearing expenses in an amount of up to $15,950. In addition, we have agreed to issue to the Placement Agent, or its designees, warrants (the “Placement Agent Warrants”) as compensation in connection with this offering to purchase a number of shares of our Common Stock equal to7.0% of the aggregate number of shares of Common Stock and Pre-Funded Warrants being offered at an exercise price equal to 125% of the combined public offering price per share of Common Stock and accompanying Series F Warrant. See the section entitled “Plan of Distribution” of this prospectus for a description of the compensation to be received by the Placement Agent.

(2)Because there is no minimum number of securities or amount of proceeds required as a condition to closing in this offering, the actual offering amount, Placement Agent fees, estimated expenses and net proceeds to us, if any, are not presently determinable and may be substantially less than the total maximum offering amounts set forth above. The amount of the proceeds to us presented in this table does not give effect to any exercise of the Series F Warrants or Placement Agent Warrants offered hereby.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Delivery of the securities to the purchasers is expected to be made on or about , 2025, subject to the satisfaction of customary closing conditions.

H.C. Wainwright & Co.

The date of this prospectus is , 2025

TABLE OF CONTENTS

You should rely only on the information contained in this prospectus. No one, including but not limited to the Placement Agent, has been authorized to provide you with information that is different from that contained in this prospectus. This prospectus is dated as of the date set forth on the cover hereof. You should not assume that the information contained in this prospectus is accurate as of any date other than that date.

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