[424B5] Theriva Biologics, Inc. Prospectus Supplement (Debt Securities)

Rhea-AI Filing Summary

Theriva Biologics filed a prospectus supplement disclosing an amendment to certain existing warrants. On October 16, 2025, the company reduced the exercise price on warrants to purchase up to 1,385,000 shares of common stock from $2.00 to $0.54 per share.

This supplement updates the company’s previously effective S-1 prospectus. The change applies only to specified “Existing Warrants” held by certain holders. Theriva’s common stock trades on the NYSE Capital Market under the symbol TOVX, and the closing price was $0.84 per share on October 15, 2025.

Insights

Capital markets analyst

Warrant strike cut to $0.54 increases likelihood of exercises.

Theriva Biologics amended certain existing warrants, lowering the exercise price from $2.00 to $0.54 for instruments covering up to 1,385,000 shares. A lower strike can make exercising more attractive when the stock trades above the exercise price.

If holders exercise, shares may be issued under these warrants and the company would receive cash equal to the exercise price per share. Actual effects depend on holder decisions and market pricing relative to $0.54.

The supplement references an already effective S-1 and confines the amendment to specified “Existing Warrants.” Subsequent disclosures may detail any exercises or resulting share issuances.

Filed pursuant to Rule 424(b)(5)

Registration No. 333-282024 

PROSPECTUS SUPPLEMENT NO. 1

(to the prospectus dated September 25, 2024)

 

Theriva Biologics, Inc.

1,385,000 Shares of Common Stock

This prospectus supplement updates, amends and supplements the prospectus contained in our Registration Statement on Form S-1, as amended, effective as of September 25, 2024 (as supplemented or amended from time to time, the “Prospectus”) (Registration No. 333-282024) relating to the offer and sale of up to 918,600 shares of common stock, par value $0.001 per share (the “Common Stock”), of Theriva Biologics, Inc. (the “Company”), 1,428,600 shares of Common Stock issuable upon the exercise of 1,428,600 common warrants to purchase shares of Common Stock (the “Existing Warrants”), 510,000 pre-funded warrants to purchase up to 510,000 shares of common stock, and 1,938,600 shares of Common Stock underlying the Existing Warrants and pre-funded warrants purchased by investors in a best efforts public offering that was consummated on or about September 27, 2024. This Prospectus Supplement No. 1 (the “Prospectus Supplement”) is being filed in connection with an amendment to certain of the Existing Warrants as described below under “Amendments to Existing Warrants.” Capitalized terms used in this Prospectus Supplement and not otherwise defined herein have the meanings specified in the Prospectus.

This Prospectus Supplement is not complete without the Prospectus. This Prospectus Supplement should be read in conjunction with the Prospectus, which is to be delivered with this Prospectus Supplement, and is qualified by reference thereto, except to the extent that the information in this Prospectus Supplement updates or supersedes the information contained in the Prospectus. Please keep this Prospectus Supplement with your Prospectus for future reference.

Our shares of Common Stock are listed on the NYSE Capital Market under the symbol “TOVX”. On October 15, 2025, the closing price for our shares of Common Stock on the NYSE Capital Market was $0.84 per share.

Investing in our securities involves a high degree of risk. Before deciding whether to invest in our securities, you should consider carefully the risks and uncertainties under the heading “Risk Factors” beginning on page 6 of the Prospectus.

Neither the SEC nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of the Prospectus or this Prospectus Supplement. Any representation to the contrary is a criminal offense.

AMENDMENTS TO EXISTING WARRANTS

This Prospectus Supplement is being filed to disclose the following:

On October 16, 2025, we entered into an amendment with certain holders of Existing Warrants to purchase up to 1,385,000 shares of Common Stock held in the aggregate by such holders in order to amend the exercise price under such Existing Warrants from $2.00 to $0.54 per share.

The date of this Prospectus Supplement is October 16, 2025.

FAQ

What did Theriva Biologics (TOVX) change in this supplement?

It amended certain existing warrants, reducing the exercise price from $2.00 to $0.54 per share for warrants covering up to 1,385,000 shares.

How many shares are covered by the amended TOVX warrants?

The amendment applies to warrants to purchase up to 1,385,000 shares of common stock.

What is the new exercise price for the amended TOVX warrants?

The new exercise price is $0.54 per share, reduced from $2.00.

When was the TOVX warrant amendment executed?

The company entered into the amendment on October 16, 2025.

Where is TOVX listed and what was the latest closing price cited?

TOVX is listed on the NYSE Capital Market. The closing price cited was $0.84 per share on October 15, 2025.

Does this supplement relate to a prior registration?

Yes. It updates an effective S-1 prospectus and discloses changes to specified “Existing Warrants.”