Note 9 — Convertible Preferred Stock and Stockholders’ Equity

Authorized Capital

As of June 30, 2026 and December 31, 2025, the Company is authorized to issue 250,000,000 shares and 10,000,000 shares of common stock and preferred stock, respectively, with a par value of $0.00001 for both common stock and preferred stock.

At June 30, 2026 and December 31, 2025, the Company had designated 1,150,000 shares, 10,000 shares, 2,700,000 shares, 10,000 shares, 32,000 shares, and 10,000 shares of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, Series C Preferred Stock, Series D Preferred Stock, and Series E Preferred Stock, respectively.

Preferred Stock

Series Seed Convertible Preferred Stock

The Company has 1,150,000 shares of preferred stock designated as Series Seed Preferred Stock (“Series Seed”) and there are no shares of Series Seed outstanding as of June 30, 2026 and December 31, 2025.

Series A Convertible Preferred Stock

On September 29, 2023, the Company filed a Certificate of Designations of Rights and Preferences of Series A Preferred Stock of the Company (the “Series A Certificate of Designations”) with the State of Delaware to designate and authorize the issuance of up to 10,000 shares of Series A Preferred Stock.

On October 3, 2023, the Company issued 3,000 shares of Series A Convertible Preferred Stock in exchange for the settlement of $3.0 million in notes payable due to Veru, Inc.

On September 24, 2024, Veru converted all 3,000 shares of Series A Convertible Preferred Stock into 33 shares of the Company’s common stock per the stated conversion ratio. There were 0 shares of Series A Convertible Stock outstanding as of June 30, 2026 and December 31, 2025.

Series B Convertible Preferred Stock

In connection with the PMX acquisition on December 15, 2023, the Company issued 2,696,729 shares of Series B Convertible Preferred Stock, which were initially convertible into approximately 1,586 shares of common stock, subject to stockholder approval on September 5, 2024. All Series B Preferred Stock was fully converted into common stock on September 24, 2024. As of June 30, 2026 and December 31, 2025, no Series B Preferred Stock remains outstanding.

Series C Convertible Preferred Stock

On October 1, 2024, the Board of Directors 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, $225.28, subject to adjustment as provided in the Certificate of Designations.

On July 16, 2025, the Company exercised its voluntary Series C Preferred Stock adjustment right to lower the conversion price of the Series C Preferred Stock to $175, and holders of 1,920 shares of Series C Preferred Stock agreed to convert their shares into shares of Common Stock. During the year ended December 31, 2025, 1,369 shares of Series C Preferred Stock were redeemed for an aggregate amount of $1.71 million, 1,920 shares of Series C Preferred Stock were converted into common stock and 203 shares of Series C Preferred Stock were exchanged into 244 shares of Series D Preferred Stock (as defined below). As of June 30, 2026 and December 31, 2025, 7 shares of Series C Preferred Stock remain outstanding, with a carrying value of $1.7 thousand, as reflected in the accompanying consolidated balance sheet.

Series D Preferred Stock

On September 22, 2025, the Company entered into a securities purchase agreement (the “Series D Securities Purchase Agreement” and the financing contemplated therein, the “Series D PIPE Financing”) with eleven institutional investors, and sold or exchanged debt, to such investors (collectively, the “Series D PIPE Investors”) 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 Series D PIPE Investors’ irrevocable commitment to purchase shares of the Series D Preferred Stock, and warrants (the “Series D Warrants”) to purchase 872,567 shares of Common Stock, (the Series D Preferred Stock together with the Series D Warrants, the “Series D 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 Series D Warrants is $0.9716, and the Series D Warrants are exercisable beginning on the issuance date and expire on the third anniversary of the issuance date.

The Series D Preferred Stock was determined to be more akin to an equity-like host than a debt-like host and was classified as permanent equity as it was not redeemable in any manner that would require classification outside of permanent equity pursuant to ASC 480-10-S99. The Series D Preferred Stock was recorded on the accompanying consolidated balance sheet at its par value. Certain embedded share-settled redemption features within the Series D Preferred Stock were bifurcated and accounted for separately a derivative liability.

The Series D Warrants and certain embedded share-settled redemption features of the Series D Preferred Stock issued were determined to be liability-classified instruments pursuant to ASC 480 and ASC 815. The embedded features of the Series D Preferred Stock were bifurcated and accounted for separately as derivative liabilities. The Company measured the warrant liabilities and bifurcated derivative liabilities at fair value on a recurring basis using Level 3 inputs as of September 22, 2025 (the issuance date), December 23, 2025 (amended warrants date), December 31, 2025 (derivative liabilities fair value date) and June 30, 2026, respectively. See Note 8 for further information regarding the valuation methodology and assumptions used in determining the fair value of the warrant and derivative liabilities.

The Series D Preferred Stock has no voting rights. The Series D Preferred Stock are convertible into common stock at the election of the holders of the Series D Preferred Stock at any time at an initial conversion price of $184.45 per share. The conversion price is subject to customary adjustments for stock dividends, stock splits, reclassifications, stock combinations and the like (subject to certain exceptions), anti-dilution provisions, and a floor price of $0.5322.

The Series D Preferred Stock is not redeemable by the holder except in the event of 1) a liquidation, dissolution, or winding up, or 2) the Series D Preferred Stock is redeemable for common stock of the Company upon the occurrence of a change in control. Holders of the Series D Preferred Stock shall be entitled to receive dividends as authorized and declared by the Company’s Board of Directors, payable in cash, securities, or in other assets as determined by the Company’s Board of Directors.

In the event of the Company’s liquidation, dissolution, or winding up, holders of the Series D Preferred Stock will be entitled to receive out of the assets, whether capital or surplus, an amount equal to the stated value of the Series D Preferred Stock, plus any accrued and unpaid dividends thereon and any other fees or liquidated damages owed before any distribution or payment shall be made to the holders of any junior securities.

During the six months ended June 30, 2026, holders of Series D Preferred Stock converted 8,169 shares into 375,977 shares of common stock. As of June 30, 2026 and December 31, 2025, 8,156 and 16,325 shares of Series D Preferred Stock remain outstanding, respectively.

Series E Preferred Stock

On October 1, 2025, Onconetix entered into, and sold to institutional investor(s) (collectively, the “PIPE Investors”), pursuant to a securities purchase agreement (the “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 (the “Common Stock”) and warrants to purchase 405,045 shares of Common Stock (the “Warrants” and, together with the Series E Preferred Stock, the “PIPE Securities”), for an aggregate purchase price of approximately $6.25 million and net cash proceeds of $6.2 million. Such investment is referred to as the “PIPE Financing”. The exercise price of the Series E Warrants is $0.9716, and the Series E Warrants are exercisable beginning on the issuance date and expire on the third anniversary of the issuance date.

The Series E Preferred Stock was determined to be more akin to an equity-like host than a debt-like host and was classified as permanent equity as it was not redeemable in any manner that would require classification outside of permanent equity pursuant to ASC 480-10-S99. The Series E Preferred Stock was recorded on the accompanying consolidated balance sheet at its par value. Certain embedded share-settled redemption features within the Series E Preferred Stock were bifurcated and accounted for separately a derivative liability.

The Series E Warrants and certain embedded share-settled redemption features of the Series E Preferred Stock issued were determined to be liability-classified instruments pursuant to ASC 480 and ASC 815. The embedded features of the Series E Preferred Stock were bifurcated and accounted for separately as derivative liabilities. The Company measured the warrant liabilities and bifurcated derivative liabilities at fair value on a recurring basis using Level 3 inputs as of October 1, 2025 (the issuance date), December 23, 2025 (amended warrants date) and December 31, 2025 (derivative liabilities fair value date), and June 30, 2026. See Note 8 for further information regarding the valuation methodology and assumptions used in determining the fair value of the warrant and derivative liabilities.

The Series E Preferred Stock has no voting rights. The Series E Preferred Stock are convertible into common stock at the election of the holders of the Series E Preferred Stock at any time at an initial conversion price of $192.88 per share. The conversion price is subject to customary adjustments for stock dividends, stock splits, reclassifications, stock combinations and the like (subject to certain exceptions), anti-dilution provisions, and a floor price of $0.298.

The Series E Preferred Stock is not redeemable by the holder except in the event of 1) a liquidation, dissolution, or winding up, or 2) the Series E Preferred Stock is redeemable for common stock of the Company upon the occurrence of a change in control. Holders of the Series E Preferred Stock shall be entitled to receive dividends as authorized and declared by the Company’s Board of Directors, payable in cash, securities, or in other assets as determined by the Company’s Board of Directors.

In the event of the Company’s liquidation, dissolution, or winding up, holders of the Series E Preferred Stock will be entitled to receive out of the assets, whether capital or surplus, an amount equal to the stated value of the Series E Preferred Stock, plus any accrued and unpaid dividends thereon and any other fees or liquidated damages owed before any distribution or payment shall be made to the holders of any junior securities.

As of December 31, 2025, all 7,813 shares of Series E Preferred Stock remained outstanding. As of June 30, 2026, all 7,813 shares of Series E Preferred Stock were converted into 668,021 shares of Common Stock.

October 2024 ELOC

Concurrently, on October 2, 2024, the Company entered into a Common Stock Equity Line of Credit Purchase Agreement (the “October 2024 ELOC Purchase Agreement”) with an institutional investor (the “October 2024 ELOC Investor”), whereby the Company may sell up to $25,000,000 of the Company’s new issued Common Stock. Pursuant to the October 2024 ELOC Purchase Agreement, the October 2024 ELOC Investor shall purchase from the Company up to the lesser of (i) $25.0 million in shares of our Common Stock and (ii) 390 shares, representing 19.99% of the total number of shares of Common Stock outstanding immediately prior to the execution of the October 2024 ELOC Purchase Agreement. Pursuant to the October 2024 ELOC Purchase Agreement, 30% of the gross proceeds to the Company from any sale of common stock thereunder must be applied towards the redemption of the Series C Redeemable Preferred Stock.

During the three months ended June 30, 2026 and 2025, the Company received proceeds of $4.3 million and $1.4 million under the ELOC, respectively. During the six months ended June 30, 2026 and 2025, the Company received proceeds of $4.3 million and $6.4 million under the ELOC, respectively.

Common Stock

As of June 30, 2026 and December 31, 2025 there were 3,793,676 and 31,201 shares of common stock issued, respectively, and 3,793,673 and 31,198 shares of common stock outstanding, respectively.

Treasury Stock

On November 10, 2022, the Board approved a stock repurchase program (the “Repurchase Program”) to allow the Company to repurchase up to 125,000 shares of common stock with a maximum price of $1.00 per share, with discretion to management to make purchases subject to market conditions. On November 18, 2022, the Board approved an increase to the maximum price to $2.00 per share. There was no expiration date for this program and prices are not adjusted for the reverse stock split to comply with the program.

There were no repurchases of common stock during the six months ended June 30, 2026 and 2025.

On November 13, 2024, the Board terminated the Repurchase Program.

Warrants

The following summarizes the Company’s outstanding warrants, excluding contingent warrants issuable upon exercise of the outstanding warrants as of June 30, 2026:

As of June 30, 2026, the Company had outstanding warrants, which are exercisable into 24,212,655 shares of common stock. The shares of common stock underlying the outstanding warrants had an exercise price of $1.27 per share, based on the closing trading price on June 30, 2026.

On May 21, 2026, the Company effected a 1-for-10 reverse stock split of its common stock. The Series D and Series E warrants contain anti-dilution provisions that require adjustments to the exercise price and the number of shares underlying the warrants upon the occurrence of specified events. Pursuant to these provisions, following the reverse stock split, the exercise price of the affected warrants was adjusted based on the lowest volume weighted average price ("VWAP") of the Company's common stock during the 16 trading-day period following the reverse stock split, resulting in an adjusted exercise price of $0.9716 per share.

As a result of this price-reset feature, the anti-dilution adjustment increased the number of shares issuable upon exercise of the affected warrants after giving effect to the reverse stock split, rather than decreasing solely in proportion to the reverse stock split ratio. Based on the adjusted exercise price, the Company determined that an aggregate of 24,212,379 net Series D and E warrants became issuable after accounting for this adjustment.

Contingent Warrant Liabilities

As of June 30, 2026, the fair value of contingent warrant labilities includes the Series C warrants of $5,100 and those issuable upon exercise of the Inducement PIOs of approximately $20,278 totaling $25,378 included as contingent warrant liabilities in the accompanying condensed consolidated balance sheets.

As of December 31, 2025, the fair value of contingent warrant labilities includes the Series C Warrants of $6,300 and those issuable upon exercise of the Inducement PIOs of approximately $20,290 totaling $26,590 included as contingent warrant liabilities in the accompanying consolidated balance sheets.

Onconetix Equity Incentive Plans

The Company’s 2019 Equity Incentive Plan (the “2019 Plan”) was adopted by its board of directors and by its stockholders on July 1, 2019. On February 23, 2022 the Company’s board of directors adopted the Company’s 2022 Equity Incentive Plan (the “2022 Plan”), which is the successor and continuation of the Company’s 2019 Plan. Under the 2022 Plan, the Company may grant stock options, restricted stock, restricted stock units, stock appreciation rights, and other forms of awards to employees, directors, and consultants of the Company. In May 2023, the number of shares of common stock reserved for issuance under the 2022 Plan was increased to 18, and in September 2024, the number of shares of common stock reserved for issuance under the 2022 Plan was increased to 341. Stock-based awards granted during the six months ended June 30, 2025 were all granted under the 2022 Plan. There were no stock-based awards granted during the six months ended June 30, 2026. As of June 30, 2026, there are 208 shares available for issuance under the 2022 Plan.

Stock Options

There were no stock options granted during the three and six months ended June 30, 2026 and 2025.

The aggregate fair value of stock options that vested during the three and six months ended June 30, 2026, was approximately $0 and $0, respectively, compared to $46,000 and $92,000 for the same periods in 2025.

Restricted Stock

The following summarizes activity related to the Company’s restricted stock awards granted under the 2022 Plan for the six months ended June 30, 2026:

Proteomedix Stock Option Plan

Proteomedix sponsors a stock option plan (the “PMX Option Plan”) which provides common stock option grants to be granted to certain employees and consultants, as was determined by the board of directors of Proteomedix. In connection with the PMX Transaction, the Company assumed the PMX Option Plan.

Generally, options issued under the PMX Option Plan have a term of not more than 11 years and provide for a four-year vesting period. Stock options issued under the PMX Option Plan are measured at fair value using the Black-Scholes option pricing model.

There was no activity under the PMX Option Plan for the six months ended June 30, 2026 and 2025. As of June 30, 2026 and December 31, 2025, there were no outstanding stock options.

Stock-Based Compensation

Stock-based compensation expense related to stock options and restricted stock, for the three and six months ended June 30, 2026 and 2025 was as follows: