Onconetix, Inc.

This prospectus contains “forward-looking statements” within the meaning of the federal securities laws, and that involve significant risks and uncertainties. Words such as “may,” “should,” “could,” “would,” “predicts,” “potential,” “continue,” “expects,” “anticipates,” “future,” “intends,” “plans,” “believes,” “estimates,” and similar expressions, as well as statements in future tense, identify forward-looking statements. Forward-looking statements should not be read as a guarantee of future performance or results and may not be accurate indications of when such performance or results will be achieved. Forward-looking statements are based on information we have when those statements are made or management’s good faith belief as of that time with respect to future events and are subject to significant risks and uncertainties that could cause actual performance or results to differ materially from those expressed in or suggested by the forward-looking statements. Forward-looking statements are subject to a number of risks, uncertainties and assumptions in other documents we file from time to time with the SEC, specifically our most recent Annual Report on Form 10-K, our Quarterly Reports on Form 10-Q and our Current Reports on Form 8-K.

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PROSPECTUS SUMMARY

The SEC allows us to “incorporate by reference” certain information that we file with the SEC, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus, and information that we file later with the SEC will update automatically, supplement and/or supersede the information disclosed in this prospectus. Any statement contained in a document incorporated or deemed to be incorporated by reference in this prospectus shall be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained in this prospectus or in any other document that also is or is deemed to be incorporated by reference in this prospectus modifies or supersedes such statement. Any such statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus. You should read the following summary together with the more detailed information regarding our company, our Common Stock and our financial statements and notes to those statements included in this prospectus.

Our Company

We are a commercial stage biotechnology company focused on the research, development, and commercialization of innovative solutions for men’s health and oncology. Through our acquisition of Proteomedix, which closed on December 15, 2023, we own Proclarix, an in vitro diagnostic test for prostate cancer originally developed by Proteomedix and approved for sale in the European Union under the In Vitro Diagnostic Regulation (“IVDR”), which we anticipate will be marketed in the U.S. as a lab developed test through our license agreement with LabCorp.

We also own ENTADFI, an FDA-approved, once daily pill that combines finasteride and tadalafil for the treatment of BPH, a disorder of the prostate. However, in light of (i) the time and resources needed to continue pursuing commercialization of ENTADFI, and (ii) the Company’s cash runway and indebtedness, the Company has abandoned commercialization of ENTADFI and is in the process of destroying its inventory of the product. In addition, as part of cost reduction efforts and in connection with our initial pause in commercializing ENTADFI, we terminated three employees involved with the ENTADFI program, effective April 30, 2024, with such individuals to continue assisting the Company on an as-needed, consulting basis. Based on the current circumstances surrounding ENTADFI, at June 30, 2024, the ENTADFI assets were fully impaired. Refer to Note 4 in the accompanying condensed consolidated financial statements incorporated by reference in this prospectus for further discussion.

We are currently focusing our efforts on commercializing Proclarix.

Proclarix is an easy-to-use next generation protein-based blood test that can be done with the same sample as a patient’s regular Prostate-Specific Antigen (“PSA”) test. The PSA test is a well-established prostate specific marker that measures the concentration of PSA molecules in a blood sample. A high level of PSA can be a sign of prostate cancer. However, PSA levels can also be elevated for many other reasons including infections, prostate stimulation, vigorous exercise or even certain medications. PSA results can be confusing for many patients and even physicians. It is estimated over 50% of biopsies with elevated PSA are negative or clinically insignificant resulting in an overdiagnosis and overtreatment that impacts the physician’s routine, our healthcare system, and the quality of patients’ lives. Approximately 10% of all men have elevated PSA levels., commonly referred to as the diagnostic “grey zone”, of which only 20 - 40% present clinically with cancer. Proclarix is intended for use in diagnosing these patients where it is difficult to decide if a biopsy is necessary to verify a potential clinically significant cancer diagnosis. Proclarix helps doctors and patients with unclear PSA test results through the use of our proprietary Proclarix Risk Score which delivers clear and immediate diagnostic support for further treatment decisions. No additional intervention is required, and results are available quickly. Local diagnostic laboratories can integrate this multiparametric test into their current workflow because Proclarix assays use the enzyme-linked immunosorbent assay (ELISA) standard, which most diagnostic laboratories are already equipped to process.

Since our inception in October 2018 until April 2023, when we acquired ENTADFI, we devoted substantially all of our resources to performing research and development, undertaking preclinical studies and enabling manufacturing activities in support of our product development efforts, hiring personnel, acquiring and developing our technology and now halted vaccine candidates, organizing and staffing our company, performing business planning, establishing our intellectual property portfolio and raising capital to support and expand such activities.

During the third quarter of 2023, we halted our vaccine discovery and development programs, and accordingly, we now operate in one segment: commercial. The commercial segment was new in the second quarter of 2023 and is currently dedicated to the development and commercialization of Proclarix.

Given Proclarix is CE-marked for sale in the European Union, we expect to generate revenue from sales of Proclarix by 2027. Although we anticipate these sales to offset some expenses relating to commercial scale up and development, we expect our expenses will increase substantially in connection with our ongoing activities, as we:

We rely and will continue to rely on third parties for the manufacturing of Proclarix. We have no internal manufacturing capabilities, and we will continue to rely on third parties, of which the main suppliers are single-source suppliers, for commercial product.

We do not have any products approved for sale, aside from (i) Proclarix and (ii) ENTADFI, which has not generated any revenue from product sales; we have determined to abandon commercialization of ENTADFI and are in the process of destroying our inventory of the product.

To date, we have financed our operations primarily with proceeds from our sale of preferred securities to seed investors, the initial public offering (“IPO”), and subsequent offerings of debt and equity securities. We will continue to require significant additional capital to commercialize Proclarix, and to fund operations for the foreseeable future. Accordingly, until such time as we can generate significant revenue, if ever, we expect to finance our cash needs through public or private equity or debt financings, third-party (including government) funding and to rely on third-party resources for marketing and distribution arrangements, as well as other collaborations, strategic alliances and licensing arrangements, or any combination of these approaches, to support our operations.

We have incurred net losses since inception and expect to continue to incur net losses in the foreseeable future. Our net losses may fluctuate significantly from quarter-to-quarter and year-to-year, depending in large part on the timing of our preclinical studies, clinical trials and manufacturing activities, our expenditures on other research and development activities and commercialization activities. As of June 30, 2025, the Company had cash of approximately $0.3 million, a working capital deficit of approximately $11.8 million and an accumulated deficit of approximately $128.1 million. During the six months ended June 30, 2025, the Company used approximately $3.4 million in cash for operating activities. In addition, as of October 15, 2025, the Company’s cash balance was approximately $6.5 million. The Company believes that its current cash balance is sufficient to fund its operations through August 13, 2026. When the Company can again utilize the ELOC, it may be able to raise up to $17.9 million in gross proceeds remaining under the ELOC. However, given the terms of the ELOC and the uncertainty to drawdown fully from the ELOC, there are no assurances that the Company may not have funds to sustain operations for the next 12 months.

Until we generate revenue sufficient to support self-sustaining cash flows, if ever, we will need to raise additional capital to fund our continued operations, including our product development and commercialization activities related to our current and future products. There can be no assurance that additional capital will be available to us on acceptable terms, or at all, or that we will ever generate revenue sufficient to provide self-sustaining cash flows. These circumstances raise substantial doubt about our ability to continue as a going concern. The condensed consolidated financial statements incorporated by reference in this prospectus do not include any adjustment that might be necessary if the Company is unable to continue as a going concern.

Recent Developments

Reverse Stock Split

On June 13, 2025, the Company effected a reverse stock split of all shares of its issued and outstanding Common Stock at a ratio of one-for-eighty-five (1:85). The Company accounted for the reverse stock split on a retrospective basis pursuant to Accounting Standards Codification (“ASC”) 260,Earnings Per Share. All issued and outstanding common stock, common stock warrants, and share-based awards’ exercise prices and per share data have been adjusted in these condensed consolidated financial statements, on a retrospective basis, to reflect the reverse stock split for all periods presented. The number of authorized shares and par value of the preferred stock and common stock were not adjusted because of the reverse stock split.

Series C PIPE Financing

On October 1, 2024, the Board authorized the Company to create a series of 10,000 shares of preferred stock designated as “Series C convertible Preferred Stock”, with a par value of $0.00001, pursuant to the certificate of designations. At any time after the initial issuance date of Series C convertible Preferred Stock, each Preferred Share shall be convertible into validly issued, fully paid and non-assessable shares of Common Stock. The holders of Series C Preferred Stock are entitled to dividends, on an as-if converted basis, equal to and in the same form as dividends actually paid on shares of Common Stock, when and if actually paid. In addition, from and after the occurrence and during the continuance of any Triggering Event, dividends (“Default Dividends”) will accrue on the Stated Value of each Preferred Share at a rate of fifteen percent (15.0%) (the “Default Rate”) per annum. Each holder is entitled to convert any portion of the outstanding Preferred Shares held by such holder into validly issued, fully paid and non-assessable Conversion shares at the Conversion Rate, which can be determined by dividing (x) the Conversion Amount of such Preferred Share by (y) the Conversion Price, $4.5056, subject to adjustment as provided in the Certificate of Designations.

On October 2, 2024, the Company entered into, and sold, to six institutional investors (collectively, the “PIPE Investors”), pursuant to the securities purchase agreement an aggregate of 3,499 shares of Series C Preferred Stock which includes an issuance of 840 shares of Series C Preferred Stock to the lead investor in consideration for the PIPE Investors’ irrevocable commitment to purchase shares of the Series C Preferred Stock, and warrants to purchase 6,963 shares of Common Stock for aggregate net cash proceeds to the Company of $1.9 million. The exercise price of the warrants is $372.30, and the warrants are exercisable six months after the issuance date and expire on the third anniversary of the initial exercisability date.

As of June 30, 2025, an aggregate of 2,130 shares of Series C Preferred Stock were outstanding, after redemptions of 1,369 shares for an aggregate of $1.71 million. As a result of draws on the ELOC in April and June 2025, an additional 329 shares of Series C preferred stock were to be redeemed for an aggregate amount of $409,510.

On July 16, 2025, the Company exercised its voluntary Series C adjustment right to lower the conversion price of the Series C preferred stock to $3.50, and holders of 2,130 shares Series C Preferred Stock agreed to convert their shares into shares of common stock. As of September 30, 2025, 7 shares of Series C Preferred Stock were outstanding, after the exchange of 203 shares of Series C Preferred Stock into 244 shares of Series D Preferred Stock.

After the Stockholder Approval Date, if a Triggering Event occurs and is continuing at any time after the earlier of the holders’ receipt of a Triggering Event Notice and such holder becoming aware of such Triggering Event (such earlier date, the “Alternate Conversion Right Commencement Date”) and ending on the twentieth (20 th) Trading Day after the later of (x) the date of such Triggering Event is cured and (y) such holder’s receipt of a Triggering Event Notice (such ending date, the “Alternate Conversion Right Expiration Date”), and each such period, an “Alternate Conversion Right Period”), such holder may, at such holder’s option, by delivery of a Conversion Notice to the Company (the date of any such Conversion Notice, each an “Alternate Conversion Date”), convert all, or any number of Preferred Shares held by such holder into shares of Common Stock at the Alternate Conversion Price (each, an “Alternate Conversion”). Alternate Conversion Price means, with respect to any Alternate Conversion that price will be the lowest of (i) the applicable Conversion Price as in effect on the applicable Conversion Date of the applicable Alternate Conversion, and (ii) the greater of (x) the Floor Price and (y) 80% of the lowest VWAP of the Common Stock during the five (5) consecutive Trading Day period ending and including the Trading Day immediately preceding the delivery or deemed delivery of the applicable Conversion Notice (such period, the “Alternate Conversion Measuring Period”).

At any time, the Company has the right to redeem in cash all or part of the Preferred Shares then outstanding at a price (the “Company Optional Redemption Price”) equal to 125% of the greater of (i) the Conversion Amount being redeemed and (ii) the product of (1) the Conversion Rate with respect to the Conversion Amount being redeemed multiplied by (2) the greatest closing sale price of the Company’s Common Stock on any Trading Day during the period commencing on the date immediately preceding the date the Company notifies the holders of its elections to redeem and the date the Company makes the entire payment required. Upon the occurrence of a Bankruptcy Triggering Event, the Company will immediately redeem, in cash, each of the Preferred Shares then outstanding at a redemption price equal to the greater of (i) the product of (A) the Conversion Amount to be redeemed multiplied by (B) 125% and (ii) the product of (X) the Conversion Rate with respect to the Conversion Amount in effect immediately following the date of initial public announcement of such Bankruptcy Triggering Event multiplied by (y) the product of (1) 125% multiplied by (2) the greatest closing sale price of the Common Stock on any Trading Day during the period commencing on the date immediately preceding such Bankruptcy Triggering Event and ending on the date the Company pays the entire payment required.

In no event may any Preferred Shares be converted (or Warrants be exercised) and shares of Common Stock be issued to any holder if after giving effect to the issuance of shares of Common Stock upon such conversion of the Preferred Shares (or exercise of the Warrants), the holder (together with its affiliates, if any) would beneficially own more than 4.99% of the outstanding shares of Common Stock, which we refer to herein as the “PIPE Blocker”. The PIPE Blocker may be raised or lowered to any percentage not in excess of 9.99% at the option of the applicable holder of the Preferred Shares (or Warrants), except that any raise will only be effective upon 61-days’ prior notice to the Company.

Series D PIPE Financing

On September 22, 2025, the Company entered into, and sold or exchanged debt, to eleven institutional investors (collectively, the “PIPE Investors”), pursuant to a securities purchase agreement an aggregate of 16,099 shares of Series D convertible preferred stock, par value $0.00001 per share (“Series D Preferred Stock”), which includes an issuance of 500 shares of Series D Preferred Stock to the lead investor in consideration for the PIPE Investors’ irrevocable commitment to purchase shares of the Series D Preferred Stock, and warrants to purchase 4,362,827 shares of Common Stock, (together, the “PIPE Securities”), for an aggregate purchase price of approximately $12.9 million and net cash proceeds of $9.3 million. The exercise price of the warrants is $3.6896, and the warrants are exercisable beginning on the issuance date and expire on the third anniversary of the initial exercisability date.

Concurrently with entering into the Securities Purchase Agreement, the Company also entered into a registration rights agreement with the PIPE Investors, pursuant to which it has agreed to provide the PIPE Investors with certain registration rights related to the shares of Common Stock underlying the shares of Series D Preferred Stock and Warrants.

Series E PIPE Financing

On October 1, 2025, the Company entered into, and sold to institutional investor(s) (collectively, the “PIPE Investors”), pursuant to a securities purchase agreement an aggregate of 7,813 shares of Series E convertible preferred stock, par value $0.00001 per share (“Series E Preferred Stock”), which are convertible into common stock of the Company, $0.00001 par value per share and warrants to purchase 2,025,223 shares of Common Stock (together, the “PIPE Securities”), for an aggregate purchase price of approximately $6.25 million, which was also equal to the net cash proceeds. The exercise price of the warrants is $3.8576, and the warrants are exercisable beginning on the issuance date and expire on the third anniversary of the initial exercisability date.

Concurrently with entering into the Securities Purchase Agreement, the Company also entered into a registration rights agreement with the PIPE Investors, pursuant to which it has agreed to provide the PIPE Investors with certain registration rights related to the shares of Common Stock underlying the shares of Series E Preferred Stock and Warrants.

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