424B5 1 vktx-2026-09-23-424b5_co.htm 424B5 424B5

Filed Pursuant to Rule 424(b)(5)

Registration No. 333-297820

The information in this preliminary prospectus supplement is not complete and may be changed. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell, nor a solicitation of an offer to buy, the notes in any jurisdiction where the offer or sale is not permitted.

Subject to Completion, dated September 23, 2026

PRELIMINARY PROSPECTUS SUPPLEMENT

(To Prospectus dated July 29, 2026)

% Convertible Senior Notes due 2032

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We are offering $ aggregate principal amount of our % convertible senior notes due 2032. In addition, we have granted the underwriters an option, which is exercisable within 30 days after the date of this prospectus supplement, to purchase up to an additional $ aggregate principal amount of notes solely to cover over-allotments.

MATURITY; INTEREST

We will pay interest on the notes at an annual rate of %, payable semi-annually in arrears on April 15 and October 15 of each year, beginning on April 15, 2027. The notes will mature on October 15, 2032, unless earlier converted or redeemed or repurchased by us.

CONVERSION

Noteholders may convert their notes at their option only in the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on December 31, 2026, if the last reported sale price per share of our common stock exceeds 130% of the conversion price for each of at least 20 trading days during the 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter; (2) during the five consecutive business days immediately after any 10 consecutive trading day period (such 10 consecutive trading day period, the “measurement period”) in which the trading price per $1,000 principal amount of notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price per share of our common stock on such trading day and the conversion rate on such trading day; (3) upon the occurrence of certain corporate events or distributions on our common stock, as described in this prospectus supplement; (4) if we call such notes for redemption; and (5) at any time from, and including, July 15, 2032 until the close of business on the second scheduled trading day immediately before the maturity date. We will settle conversions by paying or delivering, as applicable, cash, shares of our common stock or a combination of cash and shares of our common stock, at our election, based on the applicable conversion rate(s). The initial conversion rate is shares per $1,000 principal amount of notes, which represents an initial conversion price of approximately $ per share, and is subject to adjustment as described in this prospectus supplement. If a “make-whole fundamental change” (as defined in this prospectus supplement) occurs, then we will in certain circumstances increase the conversion rate for a specified period of time.

REDEMPTION AND REPURCHASE

We will have the right, at our election, to redeem all, or any portion (subject to certain limitations described in this prospectus supplement), of the notes, at any time, and from time to time on or after October 22, 2029 and on or before the 25th scheduled trading day immediately before the maturity date, at a cash redemption price equal to the principal amount of the notes to be redeemed, plus accrued and unpaid interest, if any, to, but excluding, the redemption date, but only if the last reported sale price per share of our common stock exceeds 130% of the conversion price on (x) each of at least 20 trading days, whether or not consecutive, during the 30 consecutive trading days ending on, and including, the trading day immediately before the date we send the related redemption notice; and (y) the trading day immediately before the date we send such notice. We refer to a redemption pursuant to the provision described in the preceding sentence as a “provisional redemption.” We will also have the right, at our election, to redeem all, but not less than all, of the notes, at a cash redemption price equal to the principal amount of the notes to be redeemed, plus accrued and unpaid interest, if any, to, but excluding, the redemption date, if the principal amount of the notes then outstanding is less than 15% of the aggregate principal amount of the notes issued in this offering (including any additional notes issued pursuant to any exercise of the underwriters’ option to purchase additional notes). We refer to a redemption pursuant to the provision described in the preceding sentence as a “cleanup redemption.” In addition, calling any note for provisional redemption or cleanup redemption will constitute a make-whole fundamental change with respect to that note, in which case the conversion rate applicable to the conversion of that note will be increased in certain circumstances if it is converted after it is called for such redemption.

If a “fundamental change” (as defined in this prospectus supplement) occurs, then, except as described in this prospectus supplement, noteholders may require us to repurchase their notes at a cash repurchase price equal to the principal amount of the notes to be repurchased, plus accrued and unpaid interest, if any.

RANKING

The notes will be our senior, unsecured obligations and will be equal in right of payment with our existing and future senior, unsecured indebtedness, senior in right of payment to our existing and future indebtedness that is expressly subordinated to the notes and effectively subordinated to our existing and future secured indebtedness, to the extent of the value of the collateral securing that indebtedness. The notes will be structurally subordinated to all existing and future indebtedness and other liabilities, including trade payables, and (to the extent we are not a holder thereof) preferred equity, if any, of our subsidiaries.

CONCURRENT COMMON STOCK OFFERING

Concurrently with this offering, we are offering, pursuant to a separate prospectus supplement $ of our common stock, plus up to an additional $ of our common stock that the underwriters of the concurrent common stock offering have the option to purchase from us. The completion of this offering is not contingent on the completion of the concurrent common stock offering, and the completion of the concurrent common stock offering is not contingent on the completion of this offering.

LISTING; COMMON STOCK

No public market currently exists for the notes, and we do not intend to apply to list the notes on any securities exchange or for quotation on any inter-dealer quotation system. Our common stock is listed on the Nasdaq Capital Market under the symbol “VKTX.” On September 22, 2026, the last reported sale price of our common stock was $40.85 per share.


	Per Note	Total
Public offering price(1)	%	$
Underwriting discounts and commissions(2)	%	$
Proceeds, before expenses, to us	%	$

(1) Plus accrued interest, if any, from, and including, , 2026.

(2) We refer you to “Underwriting” beginning on page S-75 of this prospectus supplement for additional information regarding underwriting compensation.

An investment in the notes involves risks. See “Risk Factors” beginning on page S-12.

Neither the Securities and Exchange Commission nor any state or foreign securities commission or regulatory authority has approved or disapproved of the notes or the shares of our common stock, if any, issuable upon conversion of the notes or passed upon the adequacy or accuracy of this prospectus supplement or the accompanying base prospectus. Any representation to the contrary is a criminal offense.

We expect to deliver the notes in book-entry form through the facilities of The Depository Trust Company on or about , 2026.

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Book-Running Managers

Morgan Stanley J.P. Morgan

Prospectus Supplement dated , 2026.

TABLE OF CONTENTS

Prospectus Supplement


Prospectus Supplement	Page
About This Prospectus Supplement		S-1
Prospectus Supplement Summary		S-2
The Offering		S-8
Risk Factors		S-12
Disclosure Regarding Forward-Looking Statements		S-20
Market and Industry Data		S-22
Use of Proceeds		S-23
Capitalization		S-24
Description of Notes		S-26
Material U.S. Federal Income Tax Considerations		S-66
The Concurrent Common Stock Offering		S-75
Underwriting		S-76
Legal Matters		S-85
Experts		S-85
Information Incorporated by Reference		S-86
Where You Can Find More Information		S-87


Prospectus	Page
About this Prospectus		1
Disclosure Regarding Forward-Looking Statements		2
Summary		4
Risk Factors		7
Use of Proceeds		8
Description of Capital Stock		9
Description of Debt Securities		13
Description of Warrants		20
Description of Rights		22
Description of Units		23
Description of Depositary Shares		24
Legal Ownership of Securities		27
Plan of Distribution		30
Legal Matters		32
Experts		32
Where You Can Find More Information		32
Important Information Incorporated by Reference		33

About This Prospectus Supplement

This prospectus supplement and the accompanying base prospectus are part of an “automatic shelf” registration statement on Form S-3 that we filed with the U.S. Securities and Exchange Commission, or the SEC, as a “well-known seasoned issuer” as defined in Rule 405 under the Securities Act of 1933, as amended, or the Securities Act, using a “shelf” registration process. This prospectus supplement describes the specific terms of this offering. The accompanying base prospectus, including the documents incorporated by reference therein, provides general information about us, some of which, such as the section therein titled “Plan of Distribution,” may not apply to this offering. Generally, when we refer to this prospectus supplement, we are referring to both this prospectus supplement and the accompanying base prospectus, combined.

We urge you to carefully read this prospectus supplement, the accompanying base prospectus, the documents incorporated by reference herein and therein and the additional information under the headings “Information Incorporated by Reference” and “Where You Can Find More Information” before buying any of the securities being offered under this prospectus supplement. These documents contain information you should consider when making your investment decision.

You should rely only on the information contained or incorporated by reference in this prospectus supplement and the accompanying base prospectus. We have not, and the underwriters have not, authorized anyone to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. This prospectus supplement may add, update or change information contained in the accompanying base prospectus. To the extent any information in this prospectus supplement is inconsistent with the accompanying base prospectus, you should rely on the information in this prospectus supplement. The information in this prospectus supplement will be deemed to modify or supersede the information in the accompanying base prospectus and the documents incorporated by reference therein, except for those documents incorporated by reference therein which we file with the SEC after the date of this prospectus supplement.

You should not assume that the information contained or incorporated by reference in this prospectus supplement and the accompanying base prospectus is accurate on any date subsequent to the date set forth on the front cover of this prospectus supplement and the accompanying base prospectus or on any date subsequent to the date of the document incorporated by reference, as applicable. Our business, financial condition, results of operations and prospects may have changed since those dates.

We are offering to sell, and seeking offers to buy, the securities described in this prospectus supplement only in jurisdictions where offers and sales are permitted. The distribution of this prospectus supplement and the offering of the securities in certain jurisdictions may be restricted by law. Persons outside the United States who come into possession of this prospectus supplement must inform themselves about, and observe any restrictions relating to, the offering of the securities and the distribution of this prospectus supplement outside the United States. This prospectus supplement does not constitute, and may not be used in connection with, an offer to sell, or a solicitation of an offer to buy, any securities offered by this prospectus supplement by any person in any jurisdiction in which it is unlawful for such person to make such an offer or solicitation.

We further note that the representations, warranties and covenants made by us in any agreement that is filed as an exhibit to any document that is incorporated by reference into this prospectus supplement or the accompanying base prospectus were made solely for the benefit of the parties to such agreement, including, in some cases, for the purpose of allocating risk among the parties to such agreements, and should not be deemed to be a representation, warranty or covenant to you. Moreover, such representations, warranties or covenants were accurate only as of the date when made. Accordingly, such representations, warranties and covenants should not be relied on as accurately representing the current state of our affairs.

In this prospectus supplement, (i) unless otherwise indicated or required by the context, the terms “Viking,” “we,” “our,” “us” and the “Company” refer to Viking Therapeutics, Inc. and its consolidated subsidiaries and (ii) “or” is not exclusive.

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Prospectus Supplement Summary

This summary contains basic information about us and this offering. This summary highlights selected information contained elsewhere in, or incorporated by reference into, this prospectus supplement and the accompanying base prospectus. This summary is not complete and may not contain all of the information that may be important to you and that you should consider before deciding whether or not to invest in our securities. For a more complete understanding of Viking and this offering, you should carefully read this prospectus supplement and the accompanying base prospectus, including the information incorporated by reference into this prospectus supplement and the accompanying base prospectus, in their entirety. Investing in our securities involves risks that are described in this prospectus supplement under the heading “Risk Factors,” under the heading “Item 1A. Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2025, our Quarterly Report on Form 10-Q for the quarter ended March 31, 2026, our Quarterly Report on Form 10-Q for the quarter ended June 30, 2026 and in our other filings with the SEC.

Overview

We are a clinical-stage biopharmaceutical company focused on the development of novel, first-in-class or best-in-class therapies for metabolic and endocrine disorders.

In January 2022, we announced the initiation of a Phase 1 single ascending dose, or SAD, and multiple ascending dose, or MAD, clinical trial of VK2735, a novel dual agonist of the glucagon-like peptide 1, or GLP-1, and glucose-dependent insulinotropic polypeptide, or GIP, receptors. VK2735 is being developed in both oral and subcutaneous formulations for the potential treatment of various metabolic disorders such as obesity.

In March 2023, we announced the completion of the Phase 1 trial. The study was a randomized, double-blind, placebo-controlled, SAD and MAD study in healthy adults. The primary objectives of the study included evaluation of the safety and tolerability of single and multiple doses of VK2735 delivered subcutaneously and the identification of VK2735 doses suitable for further clinical development. Study investigators also evaluated the pharmacokinetics of single and multiple doses of VK2735. Based upon the results from this Phase 1 study, in September 2023, we initiated the VENTURE study, a Phase 2 clinical trial of VK2735 in patients with obesity.

The Phase 2 VENTURE study was a randomized, double-blind, placebo-controlled study to evaluate the safety, tolerability, pharmacokinetics and weight loss efficacy of VK2735, administered subcutaneously, once weekly. The 13-week study enrolled adults who were obese (BMI >= 30 kg/m2) or adults who were overweight (BMI >= 27 kg/m2) with at least one weight-related co-morbidity condition. The primary endpoint of the study was the percent change in body weight from baseline to week 13, with secondary and exploratory endpoints evaluating a range of additional safety and efficacy measures. In October 2023, we announced completion of patient enrollment in the Phase 2 VENTURE study and on February 27, 2024, we announced that patients receiving weekly doses of VK2735 demonstrated statistically significant reductions in mean body weight after 13 weeks, ranging up to 14.7% from baseline. Patients receiving VK2735 also demonstrated statistically significant reductions in mean body weight relative to placebo, ranging up to 13.1%. VK2735 demonstrated encouraging safety and tolerability following 13 weeks of once-weekly dosing.

In June 2025, we announced the initiation of two Phase 3 clinical studies to evaluate the subcutaneous formulation of VK2735, VANQUISH-1 and VANQUISH-2. In November 2025, we announced completion of patient enrollment in the VANQUISH-1 study. In March 2026, we announced the completion of patient enrollment in the VANQUISH-2 study.

In March 2023, we announced the initiation of a Phase 1 clinical study to evaluate a novel oral formulation of VK2735. The study, which was an extension of our completed Phase 1 evaluation of subcutaneously administered VK2735, evaluated daily oral doses for 28 days. In March 2024, we announced that the 28-day MAD study results highlighted positive signs of clinical activity following treatment with oral VK2735. Cohorts receiving VK2735 demonstrated dose-dependent reductions in mean body weight from baseline, ranging up to approximately 5.3%. Oral VK2735 demonstrated encouraging safety and tolerability following 28 days of once-daily dosing.

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In January 2025, we announced the initiation of a Phase 2 clinical trial of the oral tablet formulation of VK2735, and in August 2025, we announced positive top-line results from the trial. The Phase 2 VENTURE-Oral Dosing trial successfully achieved its primary and secondary endpoints, with patients receiving oral VK2735 demonstrating statistically significant reductions in body weight compared with placebo, ranging up to 12.2% from baseline. Additionally, the trial showed oral VK2735 treatment to be safe and well-tolerated through 13 weeks of daily dosing with the majority of treatment emergent adverse events being categorized as mild or moderate. We expect to initiate Phase 3 oral dosing studies in the fourth quarter of 2026.

In October 2025, we announced the initiation of an exploratory maintenance dosing study of VK2735. This study is intended to explore the feasibility of various VK2735 maintenance dosing regimens utilizing either the oral tablet or the subcutaneous formulation to sustain the initial weight loss achieved following subcutaneous dosing. In January 2026, we announced completion of enrollment in this study. In September 2026, we announced topline results from this study, which are included in the section titled “—Recent Developments—Positive Topline Results from Maintenance Study of GLP-1/GIP Agonist VK2735” below.

In March 2025, we entered into broad, multi-year manufacturing agreements, or the Manufacturing Agreements, with Corden Pharma Colorado, Inc. and its affiliates, or CordenPharma, covering both the active pharmaceutical ingredient, or API, and final finished product supply for VK2735.

Under the terms of the Manufacturing Agreements, we have secured dedicated capacity for the annual manufacture and supply of multiple metric tons of VK2735 API. In addition, CordenPharma will provide fill/finish capacity for both the injectable and oral formulations of VK2735. This includes dedicated manufacturing lines and an annual commitment to supply 100 million autoinjectors and an additional 100 million vial and syringe products for the subcutaneous formulation, as well as an annual capacity of over one billion oral VK2735 tablets. These API and final finished product capacities are further expandable at our option. In exchange for dedicated API and fill/finish capacity, we will make prepayments to CordenPharma, to be paid over the period from 2026 to 2028. These prepayments will be fully credited against future orders.

In 2024, we announced a new, internally developed Dual Amylin and Calcitonin Receptor Agonist, or DACRA, program for the treatment of obesity and highlighted the effects of treatment on body weight, food intake and metabolic profile in both healthy rats and in diet-induced obese mice. The results demonstrated that our DACRAs reduced food intake in lean rats in the period from 0 – 72 hours following a single subcutaneous dose. In April 2026, we announced that we filed an IND application for our Novel Amylin Agonist VK3019. In June 2026, we announced the initiation of a Phase 1 SAD clinical trial evaluating VK3019.

We are also developing VK2809, which is an orally available, tissue and receptor-subtype selective agonist of the thyroid hormone receptor beta, or TRß. In November 2019, we initiated the VOYAGE study, a Phase 2b clinical trial of VK2809 in patients with biopsy-confirmed non-alcoholic steatohepatitis, or NASH/MASH.

The VOYAGE study was a randomized, double-blind, placebo-controlled, multicenter trial designed to assess the efficacy, safety and tolerability of VK2809 in patients with biopsy-confirmed NASH/MASH and fibrosis ranging from stages F1 to F3. The primary endpoint of the study evaluated the relative change in liver fat content, as assessed by magnetic resonance imaging, proton density fat fraction from baseline to week 12 in subjects treated with VK2809 as compared to placebo. Secondary objectives included evaluation of histologic changes assessed by hepatic biopsy after 52 weeks of dosing.

In January 2023, we announced completion of patient enrollment in the VOYAGE study and in May 2023 we reported that the VOYAGE study successfully achieved its primary endpoint, with patients receiving VK2809 experiencing statistically significant reductions in liver fat content from baseline to Week 12 as compared to placebo.

In June 2024, we announced positive 52-week histologic data from the VOYAGE study with up to 75% of patients treated with VK2809 achieving NASH/MASH resolution with no worsening of fibrosis as compared to 29% for placebo (p=0.0001), up to 57% of VK2809-treated patients achieving ≥1-stage improvement in fibrosis with no worsening of NASH/MASH as compared to 34% for placebo (p<0.05) and up to 48% of VK2809-treated patients achieving both resolution of NASH/MASH and a ≥1-stage improvement in fibrosis as compared to 20% for placebo (p=0.01). Adverse events, including gastrointestinal-related adverse events, were similar among VK2809-treated

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patients vs. placebo at week 52 and consistent with prior data reported at week 12. VK2809 has been evaluated in eight completed clinical studies, which enrolled more than 400 subjects.

We are also developing VK0214, which is also an orally available, tissue and receptor-subtype selective agonist of TRß for X-linked adrenoleukodystrophy, or X-ALD, a rare X-linked, inherited neurological disorder characterized by a breakdown in the protective barriers surrounding brain and nerve cells. The disease, for which there is no approved treatment, is caused by mutations in a peroxisomal transporter of very long chain fatty acids, or VLCFA, known as ABCD1. As a result, transporter function is impaired and patients are unable to efficiently metabolize VLCFA. The TRß receptor is known to regulate expression of an alternative VLCFA transporter, known as ABCD2. Various preclinical models have demonstrated that increased expression of ABCD2 can lead to normalization of VLCFA metabolism. Preliminary data suggest that VK0214 stimulates ABCD2 expression in an in vitro model and reduces VLCFA levels in an in vivo model of X-ALD.

In June 2021, we initiated a Phase 1b clinical trial of VK0214 in patients with X-ALD. This trial was a multi-center, randomized, double-blind, placebo-controlled study in adult male patients with the adrenomyeloneuropathy, or AMN, form of X-ALD. The study enrolled patients across three cohorts: placebo, VK0214 20 mg daily, and VK0214 40 mg daily.

The primary objectives of the study were to evaluate the safety and tolerability of VK0214 administered once-daily over a 28-day dosing period. Secondary objectives included an evaluation of the pharmacokinetics of VK0214 following 28 days of dosing in this population. An exploratory objective was to evaluate the effects of VK0214 on plasma levels of VLCFAs in subjects with AMN. In October 2024, we announced results from the Phase 1b clinical trial, which showed VK0214 to be safe and well-tolerated following once-daily dosing over the 28-day study period. In addition, significant reductions were observed in plasma levels of VLCFAs and other lipids, as compared to placebo. Our intent is to pursue partnering or licensing opportunities for VK0214 prior to conducting additional clinical studies.

Other programs include VK5211, an orally available, non-steroidal selective androgen receptor modulator. In November 2017, we announced positive top-line results from a Phase 2 proof-of-concept clinical trial in 108 patients recovering from non-elective hip fracture surgery. Top-line data showed that the trial achieved its primary endpoint, demonstrating statistically significant, dose-dependent increases in total lean body mass, less head, following treatment with VK5211 as compared to placebo. The study also achieved certain secondary endpoints, demonstrating statistically significant increases in appendicular lean body mass and total lean body mass for all doses of VK5211, compared to placebo. VK5211 demonstrated encouraging safety and tolerability in this study, with no drug-related serious adverse events reported. Our intent is to continue to pursue partnering or licensing opportunities for VK5211 prior to conducting additional clinical studies.

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Our Development Pipeline

The following table highlights our current development pipeline:

Key: TRß, thyroid receptor beta; MASH, metabolic dysfunction-associated steatohepatitis; GLP-1, glucagon-like peptide 1; GIP, glucose-dependent insulinotropic polypeptide; X-ALD, X-linked adrenoleukodystrophy.

For a complete description of our business, financial condition, results of operations and other important information, we refer you to our filings with the SEC that are incorporated by reference in this prospectus supplement, including our Annual Report on Form 10-K for the year ended December 31, 2025, our Quarterly Report on Form 10-Q for the quarter ended March 31, 2026 and our Quarterly Report on Form 10-Q for the quarter ended June 30, 2026. For instructions on how to find copies of these documents, see the sections of this prospectus supplement titled “Incorporation by Reference” and “Where You Can Find Additional Information”.

Recent Developments

Concurrent Common Stock Offering

Concurrently with this offering, we are offering, pursuant to a separate prospectus supplement, shares of our common stock, plus up to an additional shares of our common stock that the underwriters of the concurrent common stock offering have the option to purchase from us. The completion of this offering is not contingent on the completion of the concurrent common stock offering, and the completion of the concurrent common stock offering is not contingent on the completion of this offering. Accordingly, you should not assume that the concurrent common stock offering will be consummated on the terms described in this prospectus supplement, if at all, or that we will receive any additional proceeds from the concurrent common stock offering. This prospectus supplement does not constitute an offer to sell, or the solicitation of an offer to buy, any securities being offered in the concurrent common stock offering. The prospectus supplement for the concurrent common stock offering does not constitute an offer to sell, or the solicitation of an offer to buy, any of the notes, or the shares of common stock, if any, issuable upon conversion of the notes, that we are offering pursuant to this prospectus supplement. See “The Concurrent Common Stock Offering.”

Positive Topline Results from Maintenance Study of GLP-1/GIP Agonist VK2735

On September 22, 2026, we announced positive top-line results from our maintenance study of VK2735, our dual agonist of the GLP-1 and GIP receptors. In this study, subjects receiving subcutaneous VK2735 demonstrated superior weight maintenance following the transition to less frequent dosing regimens compared with subjects transitioned to placebo. In addition, VK2735 demonstrated an encouraging safety and tolerability profile during the 12-week maintenance dosing period, with observed rates of GI-related adverse events comparable to placebo. We

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believe these results further differentiate VK2735 by demonstrating compelling weight loss maintenance via new long-term dosing regimens, including monthly and every-other-week administration. VK2735 is being developed in both subcutaneous and oral formulations for the potential treatment of various metabolic disorders such as obesity. We plan to explore oral maintenance dosing regimens in an upcoming part 2 to the current study.

Top-line study results include:

Body Weight Reductions – Induction Phase

Participants in this study were randomized to receive weekly doses of VK2735 or placebo for 21 weeks. Starting in Week 3, VK2735 doses were escalated every two weeks until final doses of 15.0 mg, 17.5 mg, 20.0 mg, or 22.5 mg were achieved. Weight loss after 21 weeks of dosing ranged from approximately 16% to 19% compared with approximately 0% for placebo (p<0.0001 vs. baseline and placebo, all cohorts). Weight loss during the induction period was progressive in each cohort, with no evidence of plateau through 21 weeks of weekly dosing.

At 21 weeks in the combined VK2735 treatment groups, the proportion of participants demonstrating 5%, 10%, 15%, and 20% weight loss were 98%, 90%, 65%, and 32% as compared with 13%, 0%, 0%, and 0% for placebo (p<0.01 vs. placebo for each). Due to the progressive nature of observed weight loss, we believe that continued weight loss is likely to be observed with longer-term once-weekly dosing, as suggested by results from the exploratory control cohort in the maintenance phase, which demonstrated approximately 22% weight loss from baseline after 33 weeks.

Body Weight Maintenance – Maintenance Phase

Following completion of the 21-week induction phase of the study, participants receiving weekly VK2735 treatment were transitioned to maintenance dosing regimens for an additional 12 weeks. During the maintenance dosing period, participants were randomized to a range of monthly (every four weeks) and every-other-week dosing regimens to evaluate the effect of less frequent dosing on weight maintenance.

Subjects randomized to every-other-week dosing regimens maintained up to 97% of mean weight loss achieved in the weekly induction period. This compares with 61% mean weight loss maintenance among subjects randomized to placebo (p<0.0001 vs. placebo). Separation from placebo was noted as early as four weeks following transition from weekly dosing.

Participants randomized to monthly dosing regimens successfully maintained up to 90% of mean weight loss achieved during the induction period, compared with 61% mean weight loss maintenance among subjects randomized to placebo (p=0.0002 vs. placebo). As with the transition to every-other-week dosing, separation from placebo was noted as early as four weeks following transition from weekly dosing.

An exploratory control arm in the study evaluated weight change in a cohort of participants who continued receiving weekly VK2735 doses of 17.5 mg (n=13). This cohort demonstrated mean weight loss of 21.7% from baseline (Week 0) (p<0.0001 vs. baseline), compared with 0.3% weight gain for placebo (p<0.0001 vs. placebo). Weight loss in this cohort was progressive through 33 weeks of treatment with no plateau observed.

Safety and Tolerability

VK2735 demonstrated highly encouraging tolerability during the maintenance phase of the trial following the transition from weekly dosing to every-other-week or monthly dosing regimens. Rates of gastrointestinal-related adverse events such as vomiting, nausea, diarrhea, and constipation were not meaningfully different from placebo over the 12-week maintenance window. Discontinuation rates, including discontinuations due to adverse events, were low during both the maintenance and induction portions of the trial.

Consistent with prior clinical studies, VK2735 also demonstrated an encouraging safety and tolerability profile during the 21-week induction phase of the trial. One subject (1%) in the induction period discontinued VK2735 treatment due to an adverse event. The most common adverse events were gastrointestinal, or GI, in nature, characterized as mild, and in-line with those expected from activation of the GLP-1 receptor. Despite the accelerated

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2-week titration schedule utilized in this study, rates of common GI adverse events such as nausea, vomiting, constipation, and diarrhea were similar to those reported in the prior Phase 2 study, which utilized 3-week titration steps. Among the combined VK2735 treatment groups, the incidence of GI-related adverse events was low and declined over time.

About the VK2735-102 Maintenance Study

The maintenance dosing study was a randomized, double-blind, placebo-controlled trial in approximately 180 adults with obesity (BMI ≥30 kg/m2) and otherwise healthy. All participants received initial weekly subcutaneous doses of VK2735 or placebo for 21 weeks. Following Week 21, participants were transitioned to a range of VK2735 maintenance dosing options including monthly, every other week, or weekly subcutaneous injections, or placebo. The objectives of the study were to evaluate the safety, tolerability, and pharmacokinetic profile of VK2735 under these various dosing regimens. Exploratory endpoints assessed change in body weight from baseline, as well as change in body weight from Week 21 to the end of the study at Week 33.

Corporate and Other Information

We were incorporated under the laws of the State of Delaware on September 24, 2012. Our principal executive offices are located at 9920 Pacific Heights Blvd, Suite 500, San Diego, CA 92121, and our telephone number is (858) 704-4660. Our website address is www.vikingtherapeutics.com. We do not incorporate the information on, or accessible through, our website into this prospectus supplement, and you should not consider any information on, or accessible through, our website as part of this prospectus supplement. We have included our website address in this prospectus supplement solely as an inactive textual reference.

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The Offering

The summary below describes the principal terms of the notes. Certain of the terms of the notes described below are subject to important limitations and exceptions that are described in more detail under the caption “Description of Notes.” As used in this section, “we,” “our” and “us” refer to Viking Therapeutics, Inc. and not to its subsidiaries.

Issuer Viking Therapeutics, Inc.

Notes $ aggregate principal amount of % convertible senior notes due 2032. We have granted the underwriters an option, which is exercisable within 30 days after the date of this prospectus supplement, to purchase up to an additional $ aggregate principal amount of notes solely to cover over-allotments.

Settlement , 2026.

Ranking The notes will be our senior, unsecured obligations and will be:

•

equal in right of payment with our existing and future senior, unsecured indebtedness;

•

senior in right of payment to our existing and future indebtedness that is expressly subordinated to the notes;

•

effectively subordinated to our existing and future secured indebtedness, to the extent of the value of the collateral securing that indebtedness; and

•

structurally subordinated to all existing and future indebtedness and other liabilities, including trade payables, and (to the extent we are not a holder thereof) preferred equity, if any, of our subsidiaries.

As of June 30, 2026, excluding our subsidiaries, we had no indebtedness for borrowed money, and our subsidiaries had approximately $79.8 million of indebtedness and other liabilities.

Maturity October 15, 2032, unless earlier repurchased, redeemed or converted.

Interest % per annum, payable semi-annually in arrears on April 15 and October 15 of each year, beginning on April 15, 2027. In addition, special interest will accrue on the notes in the circumstances described under the caption “Description of Notes—Events of Default—Special Interest as Sole Remedy for Certain Reporting Defaults”.

Conversion Rights Noteholders may convert their notes at their option only in the following circumstances:

•

during any calendar quarter commencing after the calendar quarter ending on December 31, 2026, if the last reported sale price per share of our common stock exceeds 130% of the conversion price for each of at least 20 trading days during the 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter;

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during the five consecutive business days immediately after any 10 consecutive trading day period (such 10 consecutive trading day period, the “measurement period”) in which the trading price per $1,000 principal amount of notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price per share of our common stock on such trading day and the conversion rate on such trading day;

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upon the occurrence of certain corporate events or distributions on our common stock, as described in this prospectus supplement;

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if we call such notes for redemption; and

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at any time from, and including, July 15, 2032 until the close of business on the second scheduled trading day immediately before the maturity date.

We will settle conversions by paying or delivering, as applicable, cash, shares of our common stock or a combination of cash and shares of our common stock, at our election, based on the applicable conversion rate(s). If we elect to deliver cash or a combination of cash and shares of our common stock, then the consideration due upon conversion will be determined over an observation period consisting of 25 “VWAP trading days” (as defined in this prospectus supplement). The initial conversion rate is shares per $1,000 principal amount of notes, which represents an initial conversion price of approximately $ per share, and is subject to adjustment as described in this prospectus supplement.

If a “make-whole fundamental change” (as defined in this prospectus supplement) occurs, then we will in certain circumstances increase the conversion rate for a specified period of time.

See “Description of Notes—Conversion Rights.”

Provisional Redemption We will have the right, at our election, to redeem (a “provisional redemption”) all, or any portion (subject to certain limitations described below), of the notes, at any time, and from time to time, on or after October 22, 2029 and on or before the 25th scheduled trading day immediately before the maturity date, at a cash redemption price equal to the principal amount of the notes to be redeemed, plus accrued and unpaid interest, if any, to, but excluding, the redemption date, but only if the last reported sale price per share of our common stock exceeds 130% of the conversion price on (x) each of at least 20 trading days, whether or not consecutive, during the 30 consecutive trading days ending on, and including, the trading day immediately before the date we send the related redemption notice; and (y) the trading day immediately before the date we send such notice. However, we may not redeem less than all of the outstanding notes pursuant to a provisional redemption unless at least $100.0 million aggregate principal amount of notes are outstanding and not called for redemption as of the time we send the related redemption notice. In addition, calling any note for provisional redemption will constitute a make-whole fundamental change with respect to that note, in which case the conversion rate applicable to the conversion of that note will be increased in certain circumstances if it is converted after it is called for provisional redemption. See “Description of Notes—Optional Redemption—Provisional Redemption.”

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Optional Cleanup

Redemption We will have the right, at our election, to redeem (a “cleanup redemption”) all, but not less than all, of the notes, at any time, at a cash redemption price equal to the principal amount of the notes to be redeemed, plus accrued and unpaid interest, if any, to, but excluding, the redemption date, but only if the principal amount of the notes outstanding at the time we send the related redemption notice is less than 15% of the aggregate principal amount of the notes issued in this offering (including any additional notes issued pursuant to any exercise of the underwriters’ option to purchase additional notes). In addition, calling the notes for cleanup redemption will constitute a make-whole fundamental change, which will require us to increase the conversion rate in certain circumstances for a specified period of time. See “Description of Notes—Optional Redemption—Cleanup Redemption.”

Repurchase at the Option of

the Noteholders After a

Fundamental Change If a “fundamental change” (as defined in this prospectus supplement) occurs, then, except as described in this prospectus supplement, noteholders may require us to repurchase their notes at a cash repurchase price equal to the principal amount of the notes to be repurchased, plus accrued and unpaid interest, if any, to, but excluding, the fundamental change repurchase date. See “Description of Notes—Fundamental Change Permits Noteholders to Require Us to Repurchase Notes.”

Trustee, Paying Agent and

Conversion Agent U.S. Bank Trust Company, National Association.

No Public Market The notes are a new class of securities for which no public market currently exists. We do not intend to apply to list the notes on any securities exchange or for quotation on any inter-dealer quotation system. Accordingly, a liquid market for the notes may never develop. Certain of the underwriters have advised us that they intend to make a market in the notes. However, they are not obligated to do so and may discontinue any market-making activity at any time and without notice.

The Nasdaq Capital Market

Symbol Our common stock is listed on the Nasdaq Capital Market under the symbol “VKTX.” On September 22, 2026, the last reported sale price of our common stock was $40.85 per share.

Use of Proceeds We estimate that the net proceeds to us from this offering will be approximately $ million (or approximately $ million if the underwriters exercise in full their option to purchase additional notes), after deducting the underwriting discounts and commissions and our estimated offering expenses. We intend to use the net proceeds from this offering, together with the net proceeds from the concurrent common stock offering described below, if it is consummated, for the continued clinical development, advancement and commercialization of our VK2735 and VK3019 programs and for other general research and development, working capital and general corporate purposes. We may also use a portion of the net proceeds to acquire or invest in other businesses, products and technologies that are complementary to our own, although we have no current plans, commitments or arrangements to do so. See “Use of Proceeds.”

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Concurrent Common Stock

Offering Concurrently with this offering, we are offering, pursuant to a separate prospectus supplement, shares of our common stock, plus up to an additional shares of our common stock that the underwriters of the concurrent common stock offering have the option to purchase from us. We estimate that the net proceeds to us from the concurrent common stock offering, if it is consummated, will be approximately $ million (or approximately $ million if the underwriters of the concurrent common stock offering exercise in full their option to purchase additional shares of common stock), after deducting the underwriting discounts and commissions and our estimated offering expenses.

The completion of this offering is not contingent on the completion of the concurrent common stock offering, and the completion of the concurrent common stock offering is not contingent on the completion of this offering. Accordingly, you should not assume that the concurrent common stock offering will be consummated on the terms described in this prospectus supplement, if at all, or that we will receive any additional proceeds from the concurrent common stock offering. This prospectus supplement does not constitute an offer to sell, or the solicitation of an offer to buy, any securities being offered in the concurrent common stock offering. The prospectus supplement for the concurrent common stock offering does not constitute an offer to sell, or the solicitation of an offer to buy, any of the notes, or the shares of common stock, if any, issuable upon conversion of the notes, we are offering pursuant to this prospectus supplement. See “The Concurrent Common Stock Offering.”

Risk Factors Investing in the notes involves risks. See “Risk Factors.”

Material U.S. Federal Income

Tax Considerations For a description of material U.S. federal income tax considerations of purchasing, owning, converting and disposing of the notes and owning and disposing of shares of our common stock, if any, issuable upon conversion of the notes, see “Material U.S. Federal Income Tax Considerations.”

Book-Entry Form We will initially issue the notes in the form of one or more global notes registered in the name of Cede & Co., as nominee of The Depository Trust Company (“DTC”), without interest coupons, which we will deposit with the trustee as custodian for DTC. Beneficial interests in global notes will be shown on, and transfers of global notes will be effected only through, the records maintained by DTC. Except in limited circumstances, we will not issue certificated notes. See “Description of Notes—Book Entry, Settlement and Clearance.”

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Risk Factors

Investing in the notes involves a high degree of risk. In addition to the other information included and incorporated by reference in this prospectus supplement or the accompanying prospectus, you should carefully consider the risks described or referred to below before deciding to purchase the notes. The occurrence of any of these risks may materially harm our business, results of operations and financial condition. As a result, the trading price of the notes and our common stock may decline, and you might lose part or all of your investment. As used in this section, “we,” “our” and “us” refer to Viking Therapeutics, Inc. and not to its subsidiaries.

The notes will be effectively subordinated to our existing and future secured indebtedness and structurally subordinated to the liabilities of our subsidiaries.

The notes will be our senior, unsecured obligations and will rank equal in right of payment with our existing and future senior, unsecured indebtedness, senior in right of payment to our existing and future indebtedness that is expressly subordinated to the notes and effectively subordinated to our existing and future secured indebtedness, to the extent of the value of the collateral securing that indebtedness. In addition, because none of our subsidiaries will guarantee the notes, the notes will be structurally subordinated to all existing and future indebtedness and other liabilities, including trade payables, and (to the extent we are not a holder thereof) preferred equity, if any, of our subsidiaries. As of June 30, 2026, excluding our subsidiaries, we had no indebtedness for borrowed money, and our subsidiaries had approximately $79.8 million of indebtedness and other liabilities. The indenture governing the notes will not prohibit us or our subsidiaries from incurring additional indebtedness, including senior or secured indebtedness, in the future.

If a bankruptcy, liquidation, dissolution, reorganization or similar proceeding occurs with respect to us, then the holders of any secured indebtedness that we may have in the future may proceed directly against the assets securing that indebtedness. Accordingly, those assets would not be available to satisfy any outstanding amounts under our unsecured indebtedness, including the notes, unless the secured indebtedness is first paid in full. The remaining assets, if any, would then be allocated pro rata among the holders of our senior indebtedness, including the notes. There may be insufficient assets to pay all amounts then due.

If a bankruptcy, liquidation, dissolution, reorganization or similar proceeding occurs with respect to any of our subsidiaries, then we, as a direct or indirect common equity owner of that subsidiary (and, accordingly, holders of our unsecured and unguaranteed indebtedness, including the notes), will be subject to the prior claims of that subsidiary’s creditors, including trade creditors and preferred equity holders. We may never receive any amounts from that subsidiary to satisfy amounts due under the notes.

We conduct a significant amount of our operations through our subsidiaries and will rely on our subsidiaries to make payments under the notes.

We conduct a significant amount of our operations through our subsidiaries. Accordingly, our ability to pay amounts due on the notes will depend on the cash flows of our subsidiaries and their ability to make distributions to us. None of our subsidiaries has guaranteed or otherwise become obligated with respect to the notes. Furthermore, none of our subsidiaries is under any obligation to make payments to us, and any payments to us would depend on the earnings or financial condition of our subsidiaries and various business considerations. Statutory, contractual or other restrictions may also limit our subsidiaries’ ability to pay dividends or make distributions, loans or advances to us. For these reasons, we may not have access to any assets or cash flows of our subsidiaries to make payments on the notes.

Our indebtedness and liabilities could limit the cash flow available for our operations, expose us to risks that could adversely affect our business, financial condition and results of operations and impair our ability to satisfy our obligations under the notes.

As of June 30, 2026, we had no consolidated indebtedness for borrowed money. We will incur $ million (or, if the underwriters exercise in full their option to purchase additional notes, $ million) principal amount of additional indebtedness as a result of this offering. We may also incur additional indebtedness to meet future financing needs. Our indebtedness could have significant negative consequences for our security holders and our business, results of operations and financial condition by, among other things:

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increasing our vulnerability to adverse economic and industry conditions;

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limiting our ability to obtain additional financing;

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requiring the dedication of a substantial portion of our cash flow from operations to service our indebtedness, which will reduce the amount of cash available for other purposes;

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limiting our flexibility to plan for, or react to, changes in our business;

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diluting the interests of our existing stockholders as a result of issuing shares of our common stock upon conversion of the notes; and

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placing us at a possible competitive disadvantage with competitors that are less leveraged than us or have better access to capital.

Our business may not generate sufficient funds, and we may otherwise be unable to maintain sufficient cash reserves, to pay amounts due under our indebtedness, including the notes, and our cash needs may increase in the future. In addition, future indebtedness that we may incur may contain financial and other restrictive covenants that limit our ability to operate our business, raise capital or make payments under our other indebtedness. If we fail to comply with these covenants or to make payments under our indebtedness when due, then we would be in default under that indebtedness, which could, in turn, result in that and our other indebtedness becoming immediately payable in full.

We may be unable to raise the funds necessary to repurchase the notes for cash following a fundamental change or to pay any cash amounts due upon maturity or conversion of the notes, and our other indebtedness may limit our ability to repurchase the notes or to pay any cash amounts due upon their maturity or conversion.

Noteholders may, subject to limited exceptions described in this prospectus supplement, require us to repurchase their notes following a fundamental change at a cash repurchase price generally equal to the principal amount of the notes to be repurchased, plus accrued and unpaid interest, if any. See “Description of Notes—Fundamental Change Permits Noteholders to Require Us to Repurchase Notes.” Upon maturity of the notes, we must pay their principal amount and accrued and unpaid interest in cash, unless they have been previously repurchased, redeemed or converted. In addition, upon conversion, we will satisfy part or all of our conversion obligation in cash unless we elect to settle conversions solely in shares of our common stock. We may not have enough available cash or be able to obtain financing at the time we are required to repurchase the notes or pay any cash amounts due upon their maturity or conversion. In addition, applicable law, regulatory authorities and the agreements governing our other indebtedness may restrict our ability to repurchase the notes or to pay any cash amounts due upon their maturity or conversion. Our failure to repurchase notes or to pay any cash amounts due upon their maturity or conversion when required will constitute a default under the indenture. A default under the indenture or the fundamental change itself could also lead to a default under agreements governing our other indebtedness, which may result in that other indebtedness becoming immediately payable in full. We may not have sufficient funds to satisfy all amounts due under the other indebtedness and the notes.

Not all events that may adversely affect the trading price of the notes and our common stock will result in an adjustment to the conversion rate.

We will adjust the conversion rate of the notes for certain events, including:

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certain stock dividends, splits and combinations;

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the issuance of certain rights, options or warrants to holders of our common stock;

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certain distributions of assets, debt securities, capital stock or other property to holders of our common stock;

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cash dividends on our common stock; and

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certain tender or exchange offers.

See “Description of Notes—Conversion Rights—Conversion Rate Adjustments.” We are not required to adjust the conversion rate for other events, such as third-party tender offers or an issuance of our common stock (or securities convertible into, or exercisable or exchangeable for, our common stock) for cash, that may adversely affect the trading price of the notes and our common stock. An event may occur that adversely affects the noteholders and the trading price of the notes and the underlying shares of our common stock but that does not result in an adjustment to the conversion rate.

Not all significant restructuring transactions will constitute a fundamental change, in which case you will not have the right to require us to repurchase your notes for cash.

If certain corporate events called “fundamental changes” occur, then, subject to limited exceptions described in this prospectus supplement, you will have the right to require us to repurchase your notes for cash. See “Description of Notes—Fundamental Change Permits Noteholders to Require Us to Repurchase Notes.” However, the definition of “fundamental change” is limited to specific corporate events and does not include all events that may adversely affect our financial condition or the trading price of the notes. For example, a leveraged recapitalization, refinancing, restructuring or acquisition by us may not constitute a fundamental change that would require us to repurchase the notes. Nonetheless, these events could significantly increase the amount of our indebtedness, harm our credit rating or adversely affect our capital structure and the trading price of the notes.

The increase to the conversion rate resulting from a make-whole fundamental change may not adequately compensate noteholders for the lost option value of their notes. In addition, a variety of transactions that do not constitute a make-whole fundamental change may significantly reduce the option value of the notes without a corresponding increase to the conversion rate.

If certain corporate events that constitute a “make-whole fundamental change” occur, then we will, in certain circumstances, temporarily increase the conversion rate. See “Description of Notes—Conversion Rights—Increase in Conversion Rate in Connection with a Make-Whole Fundamental Change.” The amount of the increase to the conversion rate will depend on the date on which the make-whole fundamental change becomes effective and the applicable “stock price.” While the increase to the conversion rate is designed to compensate noteholders for the lost option value of their notes resulting from a make-whole fundamental change, the increase is only an approximation and may not adequately compensate noteholders for the loss in option value. In addition, if the applicable “stock price” is greater than $ per share or less than $ per share (in each case, subject to adjustment), then we will not increase the conversion rate for the make-whole fundamental change. Moreover, we will not increase the conversion rate pursuant to these provisions to an amount that exceeds shares of our common stock per $1,000 principal amount of notes, subject to adjustment.

Furthermore, the definition of make-whole fundamental change is limited to certain specific transactions. Accordingly, the make-whole fundamental change provisions of the indenture will not protect noteholders from other transactions that could significantly reduce the option value of the notes. For example, a spin-off or sale of a subsidiary or business division with volatile earnings, or a change in our line of business, could significantly affect the trading characteristics of our common stock and reduce the option value of the notes without constituting a make-whole fundamental change that results in a temporary increase to the conversion rate.

In addition, our obligation to increase the conversion rate in connection with a make-whole fundamental change could be considered a penalty, in which case its enforceability would be subject to general principles of reasonableness and equitable remedies.

There is currently no trading market for the notes. If an active trading market for the notes does not develop, then noteholders may be unable to sell their notes at desired times or prices, or at all.

The notes are a new class of securities for which no market currently exists. We do not intend to apply to list the notes on any securities exchange or for quotation on any inter-dealer quotation system. Although certain of the underwriters have advised us that they intend to make a market in the notes, they are not obligated to do so and may discontinue any market-making activity at any time and without notice. Accordingly, an active market for the notes may never develop, and, even if one develops, it may not be maintained. If an active trading market for the notes does not develop or is not maintained, then

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the market price and liquidity of the notes will be adversely affected and noteholders may not be able to sell their notes at desired times or prices, or at all.

The liquidity of the trading market, if any, and future trading prices of the notes will depend on many factors, including, among other things, the trading price and volatility of our common stock, prevailing interest rates, our dividend yield, financial condition, results of operations, business, prospects and credit quality relative to our competitors, the market for similar securities and the overall securities market. Many of these factors are beyond our control. Historically, the market for convertible debt has been volatile. Market volatility could significantly harm the market for the notes, regardless of our financial condition, results of operations, business, prospects or credit quality.

The trading price of our common stock, the condition of the financial markets, prevailing interest rates and other factors could significantly affect the trading price of the notes.

We expect that the trading price of our common stock will significantly affect the trading price of the notes, which could result in greater volatility in the trading price of the notes than would be expected for non-convertible securities. The trading price of our common stock will likely continue to fluctuate in response to the factors described or referred to elsewhere in this section and under the caption “Disclosure Regarding Forward-Looking Statements,” among others, many of which are beyond our control.

In addition, the condition of the financial markets and changes in prevailing interest rates can have an adverse effect on the trading price of the notes. For example, prevailing interest rates have fluctuated in the past and are likely to fluctuate in the future, and we would expect an increase in prevailing interest rates to depress the trading price of the notes. An increase in short- or long-term interest rates, including as a result of a rise in actual or expected inflation, could cause the trading price of the notes to fall significantly.

The issuance or sale of shares of our common stock, including pursuant to the concurrent common stock offering, or rights to acquire shares of our common stock, could depress the trading price of our common stock and the notes.

Concurrently with this offering, we are offering $ of our common stock, plus up to an additional $ of our common stock that the underwriters of the concurrent common stock offering have the option to purchase from us. We may also conduct future offerings of common stock, preferred stock or other securities that are convertible into, or exercisable or exchangeable for, our common stock to finance our operations or fund acquisitions, or for other purposes. In addition, as of June 30, 2026, we have reserved 5,990,015 shares of our common stock issuable upon the exercise of outstanding options, 1,813,501 shares of our common stock for future issuance upon vesting of outstanding restricted stock units, 9,481,886 shares of our common stock for issuance under our 2024 Equity Incentive Plan and 5,462,753 shares of our common stock for issuance under our 2024 Employee Stock Purchase Plan. The indenture for the notes will not restrict our ability to issue additional equity securities in the future. If we issue additional shares of our common stock or rights to acquire shares of our common stock, if any of our existing stockholders sells a substantial amount of our common stock, or if the market perceives that such issuances or sales may occur, then the trading price of our common stock and, accordingly, the notes may significantly decline. In addition, our issuance of additional shares of common stock will dilute the ownership interests of our existing common stockholders, including noteholders who have received shares of our common stock upon conversion of their notes.

This offering is not contingent on the consummation of the concurrent common stock offering, and vice versa.

We will make only very limited covenants in the indenture, and these limited covenants may not protect your investment.

Many debt instruments contain provisions that restrict the borrower’s activities and operations in a manner that is designed to preserve the borrower’s ability to make payments on the related indebtedness when due. These provisions include

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financial and operating covenants, and restrictions on the payments of dividends, the incurrence of indebtedness or the issuance or repurchase of securities by the borrower or any of its subsidiaries. The indenture for the notes will not contain any of these covenants or restrictions or otherwise place any meaningful restrictions on our ability to operate our business as management deems appropriate. As a result, your investment in the notes may not be as protected as an investment in an instrument that contains some or all of these types of covenants and restrictions.

Regulatory actions, changes in market conditions and other events may adversely affect the trading price and liquidity of the notes and the ability of investors to implement a convertible note arbitrage trading strategy.

We expect that many investors in the notes, including potential purchasers of the notes from investors in this offering, will seek to employ a convertible note arbitrage strategy. Under this strategy, investors typically short sell a certain number of shares of our common stock and adjust their short position over time while they continue to hold the notes. Investors may also implement this type of strategy by entering into swaps on our common stock in lieu of, or in addition to, short selling shares of our common stock.

The SEC and other regulatory authorities have implemented various rules and taken certain actions, and may in the future adopt additional rules and take other actions, that may impact those engaging in short selling activity involving equity securities (including our common stock). These rules and actions include Rule 201 of SEC Regulation SHO, the adoption by the Financial Industry Regulatory Authority, Inc., and the national securities exchanges of a “limit up-limit down” program, the imposition of market-wide circuit breakers that halt trading of securities for certain periods following specific market declines, and the implementation of certain regulatory reforms required by the Dodd-Frank Wall Street Reform and Consumer Protection Act of 2010. Any governmental or regulatory action that restricts investors’ ability to effect short sales of our common stock or enter into equity swaps on our common stock could depress the trading price of, and the liquidity of the market for, the notes.

In addition, the liquidity of the market for our common stock and other market conditions could deteriorate, which could reduce, or eliminate entirely, the number of shares available for lending in connection with short sale transactions and the number of counterparties willing to enter into an equity swap on our common stock with a note investor. These and other market events could make implementing a convertible note arbitrage strategy prohibitively expensive or infeasible. If investors in this offering or potential purchasers of the notes that seek to employ a convertible note arbitrage strategy are unable to do so on commercial terms, or at all, then the trading price of, and the liquidity of the market for, the notes may significantly decline.

You may be subject to tax if we adjust, or fail to adjust, the conversion rate of the notes, even though you will not receive a corresponding cash distribution.

We will adjust the conversion rate of the notes in certain circumstances, including the payment of cash dividends. Adjustments (or failures to make adjustments) that have the effect of increasing your proportionate interest in our assets or earnings and profits may in some circumstances result in a deemed distribution, for U.S. federal income tax purposes, to you even though no cash or property is received. Adjustments to the conversion rate made pursuant to a bona fide, reasonable adjustment formula that has the effect of preventing the dilution of the interest of the holders of the notes, however, will generally not be considered to result in a deemed distribution to you. In addition, if we do not adjust (or adjust adequately) the conversion rate after an event that increases your proportionate interest in us, then you could be treated as having received a deemed taxable dividend. For example, if we adjust the conversion rate as a result of a dividend that is taxable to holders of our common stock, such as a cash dividend, then you may be deemed, for U.S. federal income tax purposes, to have received a taxable dividend to the extent of our earnings and profits, without the receipt of any cash or property. If a make-whole fundamental change occurs prior to the maturity date, under some circumstances, we will increase the conversion rate for notes converted in connection with that make-whole fundamental change. Such increase may also be treated as a distribution subject to U.S. federal income tax as a dividend.

If you are subject to backup withholding, or if you are a non-U.S. holder (as defined in “Material U.S. Federal Income Tax Considerations”) subject to U.S. federal withholding tax, such withholding may be withheld from or set off against subsequent payments on the notes or our common stock owned by you or from any proceeds of any subsequent sale, exchange or other disposition of such notes (including the retirement of such notes) or such common stock or other funds or assets held by you. The Internal Revenue Service has issued proposed regulations addressing the amount and timing of deemed distributions, obligations of withholding agents and filing and notice obligations of issuers, which, if adopted, could affect the U.S. federal income tax treatment of a holder of notes deemed to receive such a distribution. See “Description of

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Notes—Conversion Rights—Conversion Rate Adjustments,” “Description of Notes—Conversion Rights—Increase in Conversion Rate in Connection with a Make-Whole Fundamental Change” and “Material U.S. Federal Income Tax Considerations.”

A rating agency may not rate the notes or may assign a rating that is lower than expected.

We do not intend to seek to have the notes rated by any rating agency. However, if one or more rating agencies rate the notes and assign a rating that is lower than the rating that investors expect, or reduce their rating in the future, then the trading price of our common stock and the notes could significantly decline.

In addition, market perceptions of our creditworthiness will directly affect the trading price of the notes. Accordingly, if a ratings agency rates any of our indebtedness in the future, or puts us on credit watch, then the trading price of the notes will likely decline.

Provisions in the indenture could delay or prevent an otherwise beneficial takeover of us.

Certain provisions in the notes and the indenture could make a third-party attempt to acquire us more difficult or expensive. For example, if a takeover constitutes a fundamental change, then, except as described in this prospectus supplement, noteholders will have the right to require us to repurchase their notes for cash. In addition, if a takeover constitutes a make-whole fundamental change, then we may be required to temporarily increase the conversion rate. In either case, and in other cases, our obligations under the notes and the indenture could increase the cost of acquiring us or otherwise discourage a third party from acquiring us, including in a transaction that noteholders or holders of our common stock may view as favorable.

You may be unable to convert your notes before July 15, 2032, and the trading price of the notes could be less than the value of the consideration into which they could otherwise be converted.

Before July 15, 2032, you may convert your notes only if specific conditions are met. If these conditions are not met, then you will not be able to convert your notes and receive the cash, shares of our common stock or combination of cash and shares, as applicable, into which the notes would otherwise be convertible. As a result, the notes may trade at prices that are less than the value of the consideration into which they would otherwise be convertible.

Fluctuations in the trading price of our common stock after you elect to convert your notes may cause you to receive less valuable consideration than expected.

We will generally have the right to settle conversions in cash, shares of our common stock or a combination of cash and shares. If we elect to settle conversions solely in cash or in a combination of cash and shares, then the consideration due upon conversion will be determined based on the volume-weighted average price of our common stock during the related “observation period,” which is defined under the caption “Description of Notes—Definitions” and will consist of 25 “VWAP trading days.” Except in certain circumstances, the observation period will begin after the related conversion date. Accordingly, a considerable amount of time may lapse between the time you elect to convert your notes and the time you receive the consideration due upon conversion, and if the trading price of our common stock declines during this time, then you may receive less consideration, or consideration that is less valuable, than expected.

Your investment in the notes may be harmed if we redeem the notes.

We will have the right to redeem the notes in certain circumstances before the maturity date. See “Description of Notes—Optional Redemption.” If we redeem your notes, then you may not be entitled to benefit from potential future appreciation in the trading price of our common stock, and you may be unable to reinvest any proceeds from the redemption in comparable investments at favorable interest rates. In addition, we will be permitted, in certain circumstances, to redeem less than all of the outstanding notes in connection with a provisional redemption. A redemption of less than all of the outstanding notes will likely harm the liquidity of the market for the unredeemed notes following the redemption. Accordingly, if your notes are not redeemed in a partial redemption, then you may be unable to sell your notes at the times you desire or at favorable prices, if at all, and the trading price of your notes may decline.

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We have broad discretion in how we use the proceeds of this offering and, if it is consummated, the concurrent common stock offering, and may not use these proceeds effectively, which could affect our results of operations and cause our stock price to decline.

Although we have described in this prospectus supplement, under the caption “Use of Proceeds,” how we currently intend to use the proceeds to us from this offering and, if it is consummated, the concurrent common stock offering, our management will have broad discretion to apply the net proceeds, and investors will rely on our judgment in spending the net proceeds with only limited information about our specific intentions for the use of the net proceeds. Our management may use the proceeds in ways that do not earn a profit or otherwise result in the creation of stockholder value. In addition, pending our use of the proceeds, we may invest the proceeds from this offering in a manner that does not produce income or that may lose value.

The accounting method for the notes could adversely affect our reported financial condition and results.

The accounting method for reflecting the notes on our balance sheet, accruing interest expense for the notes and reflecting the underlying shares of our common stock in our reported diluted earnings per share may adversely affect our reported earnings and financial condition.

In accordance with applicable accounting standards, we expect that the notes we are offering will be reflected as a liability on our balance sheets, with the initial carrying amount equal to the principal amount of the notes, net of issuance costs. The issuance costs will be treated as a debt discount for accounting purposes, which will be amortized into interest expense over the term of the notes. As a result of this amortization, the interest expense that we expect to recognize for the notes for accounting purposes will be greater than the cash interest payments we will pay on the notes, which will result in lower reported income.

In addition, we expect that the shares underlying the notes will be reflected in our diluted earnings per share using the “if converted” method. Under that method, diluted earnings per share would generally be calculated assuming that all the notes were converted solely into shares of our common stock at the beginning of the reporting period, unless the result would be anti-dilutive. The application of the if-converted method may reduce our reported diluted earnings per share, and accounting standards may change in the future in a manner that may adversely affect our diluted earnings per share.

Furthermore, if any of the conditions to the convertibility of the notes is satisfied, then we may be required under applicable accounting standards to reclassify the liability carrying value of the notes as a current, rather than a long-term, liability. This reclassification could be required even if no noteholders convert their notes and could materially reduce our reported working capital.

We have not reached a final determination regarding the accounting treatment for the notes, and the description above is preliminary. Accordingly, we may account for the notes in a manner that is significantly different than described above.

Because the notes will initially be held in book-entry form, noteholders must rely on DTC’s procedures to exercise their rights and remedies.

We will initially issue the notes in the form of one or more “global notes” registered in the name of Cede & Co., as nominee of DTC. Beneficial interests in global notes will be shown on, and transfers of global notes will be effected only through, the records maintained by DTC. Except in limited circumstances, we will not issue certificated notes. See “Description of Notes—Book Entry, Settlement and Clearance.” Accordingly, if you own a beneficial interest in a global note, then you will not be considered an owner or holder of the notes. Instead, DTC or its nominee will be the sole holder of the notes. Payments of principal, interest and other amounts on global notes will be made to the paying agent, who will remit the payments to DTC. We expect that DTC will then credit those payments to the DTC participant accounts that hold book-entry interests in the global notes and that those participants will credit the payments to indirect DTC participants. Unlike persons who have certificated notes registered in their names, owners of beneficial interests in global notes will not have the direct right to act on our solicitations for consents or requests for waivers or other actions from noteholders. Instead, those beneficial owners will be permitted to act only to the extent that they have received appropriate proxies to do so from DTC or, if applicable, a DTC participant. The applicable procedures for the granting of these proxies may not be sufficient to enable owners of beneficial interests in global notes to vote on any requested actions on a timely basis.

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Holding notes will not, in itself, confer any rights with respect to our common stock.

Noteholders will generally not be entitled to any rights with respect to our common stock (including voting rights and rights to receive any dividends or other distributions on our common stock). However, noteholders will be subject to all changes affecting our common stock to the extent the trading price of the notes depends on the market price of our common stock and to the extent they receive shares of our common stock upon conversion of their notes. For example, if we propose an amendment to our charter documents that requires stockholder approval, then a noteholder will not, as such, be entitled to vote on the amendment, although the noteholder will be subject to any changes implemented by that amendment in the powers, preferences or special rights of our common stock.

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Disclosure Regarding Forward-Looking Statements

This prospectus supplement and the accompanying base prospectus, including the documents incorporated by reference herein and therein, contain forward-looking statements within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act, which statements involve substantial risks and uncertainties. Forward-looking statements generally relate to future events or our future financial or operating performance. In some cases, you can identify forward-looking statements because they contain words such as “may,” “will,” “should,” “expects,” “plans,” “anticipates,” “could,” “intends,” “target,” “projects,” “contemplates,” “believes,” “estimates,” “predicts,” “potential” or “continue” or the negative of these words or other similar terms or expressions that concern our expectations, strategy, plans or intentions. Forward-looking statements contained in this prospectus supplement and the accompanying base prospectus and the documents incorporated by reference herein and therein may include, but are not limited to, statements about:

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risks and uncertainties associated with our research and development activities, including our clinical trials and preclinical studies;

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the timing or likelihood of regulatory filings and approvals or of alternative regulatory pathways for our drug candidates;

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the potential market opportunities for commercializing our drug candidates;

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our expectations regarding the potential market size and the size of the patient populations for our drug candidates, if approved for commercial use, and our ability to serve such markets;

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estimates of our expenses, future revenue, capital requirements and our needs for additional financing;

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our ability to develop, acquire and advance our drug candidates into, and successfully complete, clinical trials and preclinical studies, and obtain regulatory approvals;

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the implementation of our business model and strategic plans for our business and drug candidates;

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the initiation, cost, timing, progress and results of future and current preclinical studies and clinical trials, and our research and development programs;

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new product candidates;

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the terms of future licensing arrangements, and whether we can enter into such arrangements at all;

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timing and receipt, or payments, of licensing and milestone revenues, if any;

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the scope of protection we are able to establish and maintain for intellectual property rights covering our drug candidates, and our ability to operate our business without infringing the intellectual property rights of others;

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regulatory developments in the United States and foreign countries;

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the performance of our third-party suppliers and manufacturers;

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our ability to maintain and establish collaborations or obtain additional funding;

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the success of competing therapies that are currently or may become available;

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our future financial performance;

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developments and projections relating to our competitors and our industry;

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our expectations regarding the completion of, and anticipated use of proceeds from, this offering and the concurrent common stock offering; and

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other risks and uncertainties, including those listed in the section titled “Risk Factors.”

We caution you that the forward-looking statements highlighted above do not encompass all of the forward-looking statements made in this prospectus supplement or the accompanying base prospectus or in the documents incorporated by reference herein and therein.

We have based the forward-looking statements contained in this prospectus supplement and the accompanying base prospectus and in the documents incorporated by reference herein and therein primarily on our current expectations and projections about future events and trends that we believe may affect our business, financial condition, results of operations and prospects. The outcomes of the events described in these forward-looking statements are subject to risks, uncertainties and other factors that could cause actual results and experience to differ from those projected, including, but not limited to, the risk factors described herein and the risk factors set forth in Part I - Item 1A, “Risk Factors”, in our Annual Report on Form 10-K for the year ended December 31, 2025, as filed with the SEC on February 11, 2026, in our Quarterly Report on Form 10-Q for the quarter ended March 31, 2026, as filed with the SEC on April 30, 2026 and in our Quarterly Report on Form 10-Q for the quarter ended June 30, 2026, as filed with the SEC on July 29, 2026 and elsewhere in the documents incorporated by reference into this prospectus supplement and the accompanying base prospectus. Moreover, we operate in a very competitive and challenging environment. New risks and uncertainties emerge from time to time, and it is not possible for us to predict all risks and uncertainties that could have an impact on the forward-looking statements contained in this prospectus supplement and the accompanying base prospectus and in the documents incorporated by reference herein and therein. We cannot assure you that the results, events and circumstances reflected in the forward-looking statements will be achieved or occur, and actual results, events or circumstances could differ materially from those described in the forward-looking statements.

The forward-looking statements contained in this prospectus supplement and the accompanying base prospectus and in the documents incorporated by reference herein and therein relate only to events as of the date on which the statements are made. We do not undertake any obligation to release publicly any revisions to such forward-looking statements to reflect events or circumstances after the date of this prospectus supplement or to reflect the occurrence of unanticipated events. We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements and you should not place undue reliance on our forward-looking statements. Our forward-looking statements do not reflect the potential impact of any future acquisitions, mergers, dispositions, joint ventures, other strategic transactions or investments we may make.

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Market and Industry Data

This prospectus supplement and the accompanying base prospectus and the information incorporated by reference herein and therein contain statistical data, estimates, forecasts, projections and other information concerning our industry, our business and the markets for certain diseases, including data regarding the estimated size of those markets and the incidence and prevalence of certain medical conditions. Information that is based on statistical data, estimates, forecasts, projections, market research or similar methodologies is inherently subject to uncertainties and actual events or circumstances may differ materially from events and circumstances reflected in this information. Unless otherwise expressly stated, we obtained this industry, business, market and other data from reports, research surveys, medical and general publications, government data, studies and similar data prepared by market research firms and other third parties. These third parties may, in the future, alter the manner in which they conduct surveys and studies regarding the markets in which we operate our business. The market and other estimates included in this prospectus supplement and the accompanying base prospectus and the information incorporated by reference herein and therein, as they relate to projections, involve numerous assumptions, are subject to risks and uncertainties, and are subject to change based on various factors, including those discussed in the section of this prospectus supplement and the accompanying base prospectus titled “Risk Factors” and in the other information contained or incorporated by reference herein and therein.

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