Pfizer's monthly GLP-1 hits its Phase 2b endpoint in VESPER-3

Pfizer reported positive topline results on February 3, 2026, from VESPER-3, a Phase 2b study of PF-08653944 (PF'3944, previously called MET-097i), an ultra-long-acting injectable GLP-1 receptor agonist being developed for both weekly and monthly dosing ^[1]. The trial met its primary endpoint, with up to 12.3% mean placebo-adjusted weight loss at week 28 ^[1].

VESPER-3 is an ongoing 64-week randomized, double-blind, placebo-controlled trial in adults with obesity or overweight who do not have type 2 diabetes ^[1]. It has five arms of roughly 54 participants each: four different titration-to-monthly regimens and placebo ^[1]. Everyone assigned to active drug started with weekly injections and up to two titration steps through week 12, then switched to monthly injections at a four-fold equivalent dose through week 28 ^[1]. The specific regimens were Arm 1 (0.4 mg weekly / 0.8 mg weekly / 3.2 mg monthly), Arm 2 (0.8 mg weekly / 3.2 mg monthly), Arm 3 (0.4 / 0.8 / 1.2 mg weekly / 4.8 mg monthly), Arm 4 (0.6 / 1.2 mg weekly / 4.8 mg monthly), and Arm 5 (placebo) ^[1].

All four active regimens beat placebo on weight reduction from randomization to week 28 (P < 0.001) ^[1]. Arms 1 and 3 — the low and medium monthly maintenance regimens Pfizer plans to carry into Phase 3 — produced 10% and 12.3% placebo-adjusted weight loss respectively, using what Pfizer calls the efficacy estimand ^[1]. Pfizer said weight loss continued after the switch from weekly to monthly dosing, with no plateau observed at week 28, and that it expects further weight loss as the study runs to week 64 ^[1].

Safety and tolerability so far

Pfizer described the safety profile through week 28 as consistent with the GLP-1 class ^[1]. Gastrointestinal treatment-emergent adverse events were predominantly mild or moderate, with no more than one instance of severe nausea or vomiting in any dose group and no instances of severe diarrhea ^[1]. Across Arms 1 and 3, five participants total discontinued treatment because of adverse events during the weekly phase and five more during the monthly phase; there were zero such discontinuations in the placebo group ^[1].

Several things are not yet public. Pfizer's release gives placebo-adjusted figures, not total percentage weight loss for each arm, and it does not report baseline weight, completion rates, or the full adverse-event tables ^[1]. There is no head-to-head comparison with semaglutide (Ozempic, Wegovy, Rybelsus) or tirzepatide (Mounjaro, Zepbound) in this trial ^[1]. Detailed results are scheduled for presentation on June 6, 2026, at the 86th Scientific Sessions of the American Diabetes Association ^[1].

Why it matters for patients

Every approved GLP-1 injectable in this class is taken weekly. A monthly injection would mean 12 shots a year instead of 52, which changes the day-to-day routine of treatment, refill timing, and travel planning for people who stay on these drugs long term. Pfizer's stated goal for VESPER-3 was to show that weight loss keeps going after the dosing interval is stretched four-fold, and that tolerability holds up when a month's worth of drug is given at once ^[1].

That second point matters because larger, less frequent doses could in principle concentrate nausea and vomiting around injection days. In this trial, Pfizer reported that severe GI events were rare and discontinuations were in the single digits across the two regimens it plans to advance ^[1]. But these are topline numbers from arms of about 54 people each, not peer-reviewed data, and they cover 28 weeks of a 64-week study ^[1].

Nothing here is available by prescription. PF'3944 is investigational, and Phase 3 results would be needed before any regulatory filing ^[1].

What happens next

Pfizer said it remains confident in including a higher 9.6 mg monthly maintenance dose in Phase 3, according to Jim List, MD, PhD, the company's Chief Internal Medicine Officer ^[1]. Ten Phase 3 trials of PF'3944 are expected to advance in 2026, including the already-initiated VESPER-4 (weekly dosing, obesity or overweight without type 2 diabetes), the planned VESPER-5 (weekly, with type 2 diabetes), the planned VESPER-6 (monthly), and at least seven more studies aimed at comorbidities and access ^[1]. Pfizer, which recently acquired Metsera and signed a license agreement with YaoPharma, says it plans 20-plus trials in 2026 across a pipeline that also includes an amylin analog, PF'3945 (MET-233i), and a GIPR agonist, PF-08654696 (MET-034i) ^[1]. Full VESPER-3 data are due June 6, 2026 ^[1].