Phathom Pharmaceuticals Vonoprazan Phase 3 Heartburn Trial Starts September 25, 2026: Non-Erosive GERD Study

Phathom Pharmaceuticals (PHAT) has a Phase 3 trial reaching its expected start date of September 25, 2026, according to trial registration data tracked by BioSniper since September 2, 2026. The study evaluates vonoprazan 10 mg against placebo for relief of episodic heartburn in patients with symptomatic non-erosive gastroesophageal reflux disease over 24 weeks — a lifecycle-extension study for a drug that already carries an FDA advisory committee record and approved-NDAs in our tracker. For a company with a market capitalization of roughly $763 million in our snapshot, this preview covers the registered design, the verified program history, and the unknowns.

The event

The trial is registered in our catalyst dataset as:

"A Phase 3, Randomized, Double-Blind, Multicenter Study to Evaluate the Efficacy and Safety of Vonoprazan 10 mg Compared to Placebo for Relief of Episodic Heartburn in Subjects With Symptomatic Non-Erosive Gastroesophageal Reflux Disease Through 24 Weeks"

The expected start date — September 25, 2026 — is recorded with "exact" date confidence. As of publication, no actual start is recorded in our data; the verified fact is the registered plan, eight days out.

What's verified

• Company: Phathom Pharmaceuticals, Inc., ticker PHAT, active listing status.
• Event type: Phase 3 trial start.
• Expected date: September 25, 2026, "exact" confidence.
• First tracked: September 2, 2026.
• Design elements from the registered title: Phase 3; randomized; double-blind; multicenter; vonoprazan 10 mg versus placebo; endpoint relief of episodic heartburn; population symptomatic non-erosive gastroesophageal reflux disease; duration through 24 weeks; efficacy and safety named as measures.
• Drug: vonoprazan (parsed from the registered title), with a resolved canonical drug page in our system.
• Vonoprazan trial footprint (drug-database linkage resolved for this article): 8 tracked trials — by phase: 3 Phase 1, 1 Phase 2, 2 Phase 3, plus one unknown and one N/A; by status: 5 completed, 1 recruiting, 1 active-not-recruiting, 1 not yet recruiting. Earliest registered start March 1, 2016; latest registered start September 25, 2026 — this study.
• Institutional ownership (13F): no 13F snapshot is available in our data for this name; we report that as-is rather than infer.

What remains unknown

• Enrollment size: UNKNOWN in our data.
• Actual start: not yet recorded.
• Results: any efficacy outcome is unknown and unpredicated.

Platform context: an approved drug expanding outward

What distinguishes this start in our tracker is the commercial base behind it. Vonoprazan's record in our data already includes:

• An FDA advisory committee record — "AdCom: VOQUEZNA (vonoprazan) tablets" dated June 6, 2025, outcome not recorded in our data.
• Three approved NDA patent-expiry records, all dated May 3, 2032 (NDA215151, NDA215152, NDA215153) — the commercial franchise this Phase 3 would extend.
• An eosinophilic esophagitis Phase 2 — vonoprazan 20 mg versus placebo over 12 and 24 weeks — started October 30, 2025 (confirmed), the most recent prior registration in the GI expansion.
• A formulation Phase 1 — orally disintegrating tablet bioavailability work — started February 14, 2025 (confirmed).

The pattern our data shows is lifecycle management in the classic shape: an approved potassium-competitive acid blocker (the marketed VOQUEZNA franchise, per the AdCom record) pushing into adjacent indications — EoE in Phase 2, and now episodic heartburn in non-erosive GERD in Phase 3. Symptomatic non-erosive GERD is the largest patient pool in the reflux spectrum; the 10 mg dose and 24-week window are the registered facts, and the commercial stakes are the context our market-cap snapshot frames without predicting.

Two dose-and-duration comparisons sit inside the same dataset. This Phase 3 registers vonoprazan at 10 mg through 24 weeks for episodic heartburn in non-erosive GERD; the EoE Phase 2 started October 2025 registered 20 mg over 12 and 24 weeks. Same molecule, adjacent GI indication, double the dose in the esophagitis setting — a registered contrast our data documents without explaining, since dosing rationale is not a field we track. The ten-year span of the drug's trial footprint (earliest registered start March 1, 2016; latest this study) further frames how much accumulated investigation stands behind what is, for Phathom, a still-mid-cap commercialization story.

How to track it

• Phathom Pharmaceuticals company page: https://biosniper.co/company/PHAT
• This trial-start event page: https://biosniper.co/calendar/event/5790823
• Vonoprazan drug page: https://biosniper.co/drug/vonoprazan

Bottom line

A registered Phase 3 start on September 25, 2026 puts vonoprazan 10 mg against placebo for episodic heartburn in symptomatic non-erosive GERD over 24 weeks — the eighth tracked trial in the drug's footprint and the newest expansion of a franchise that already carries an AdCom record, three approved NDAs, and a confirmed EoE Phase 2 started in October 2025. Enrollment size, actual start, and results are unknowns in our data. The design skeleton above is exactly what the registration states.