Pfizer unveils new Phase 2b obesity data to push toward a monthly weight-loss injection

Pfizer is moving to differentiate its next obesity drug by targeting a monthly dosing schedule, presenting new clinical readouts meant to show that weight loss can continue after patients switch from a weekly injection to an every-four-weeks maintenance dose. The company unveiled the latest results for berobenatide, an investigational GLP-1 receptor agonist peptide, during a Saturday session tied to the American Diabetes Association’s annual scientific meeting. Pfizer’s goal is to position berobenatide as a potential first-in-class monthly option within a market where weekly injections currently set the benchmark for weight reduction.

In Pfizer’s Phase 2b VESPER-1 study, the company highlighted results from an exploratory extension. Patients received once-weekly berobenatide and, in a 32-week segment of the program, achieved non-placebo-adjusted weight loss of about 15.9% on the 2.4 mg dose, with Pfizer saying there was no plateau observed by that point. VESPER trials are mid-stage studies designed to test dose strategies and to build a basis for Phase 3 dosing regimens.

For the monthly strategy specifically, Pfizer pointed to VESPER-3, an ongoing 64-week Phase 2b trial in people with obesity or overweight without type 2 diabetes. Pfizer reported placebo-adjusted weight loss at week 28 of 10% for one monthly maintenance regimen and 12.3% for another, and said it did not observe a plateau at week 28, suggesting continued weight loss may extend as the study continues through later weeks. In Pfizer’s framing, these results support continued development of monthly dosing and help define the doses it plans to test in larger Phase 3 trials.

Pfizer also emphasized what it calls a patient-friendly administration profile. In its release, the company said the program achieved favorable tolerability indicates, including low rates of gastrointestinal adverse events and discontinuations, even as dosing was escalated rapidly without an allowed step-down. The release further described the maintenance presentation as a low-volume injection, stating the monthly option would involve a 0.5 mL injection volume, alongside what it described as convenience and scalability advantages.

The company tied the new data to a broader obesity buildout for 2026. Pfizer said it plans to advance 10 Phase 3 studies for berobenatide in 2026, as part of what it described as a 20-plus trial program across obesity and related comorbidities. The Phase 3 plan includes VESPER-6, a pivotal study evaluating once-monthly berobenatide and noted as open for enrollment, and additional planned studies aimed at conditions including knee osteoarthritis and obstructive sleep apnea. Separately, StreetInsider reported Pfizer executives linked the effort to its manufacturing footprint and said berobenatide’s requirements could reduce active ingredient needs versus some rival therapies, though those points were not fully detailed in Pfizer’s press release.

Pfizer’s effort follows its 2025 acquisition of Metsera, a biotech with obesity-focused candidates. Under the Metsera deal announced in September 2025, Pfizer said it would acquire Metsera for $47.50 per share in cash, with an initial enterprise value of about $4.9 billion and additional contingent value rights that could add up to further payments tied to clinical and regulatory milestones. The transaction also positioned Metsera’s weekly and monthly injectable GLP-1 program, MET-097i, as a key input into Pfizer’s longer-term obesity pipeline development.

Market context adds urgency to the monthly proposition. Statnews reported that the VESPER-3 data presented at the ADA meeting showed continued weight loss after the weekly-to-monthly transition and had not hit a plateau by 28 weeks, but it also noted that the weight-loss rate at the same time point was still lower than what was seen in the pivotal trial of Eli Lilly’s Zepbound. Pfizer, meanwhile, has continued to frame monthly dosing as an adherence and convenience advantage relative to weekly injectables.

Still, important details remain uncertain. The reported efficacy figures are from Phase 2b interim analyses, and while Pfizer reported no plateau by week 28 in the monthly-maintenance portion of VESPER-3, it did not disclose longer-term durability, comparative results versus specific weekly competitors, or a complete side-effect profile in the briefing materials tied to the announcement. Regulatory timing and approval likelihood for a monthly GLP-1 option are also not determined, and Phase 3 outcomes could shift dosing, labeling, or risk-benefit conclusions.

For investors and patients, the next checkpoint is Pfizer’s Phase 3 execution across the VESPER program, including enrollment and dosing strategy for once-monthly treatment in VESPER-6. The company is also likely to emphasize whether monthly maintenance preserves tolerability over longer treatment periods and how it performs against evolving standards set by weekly obesity drugs.