Pfizer details monthly berobenatide data and plans 10 Phase 3 trials in 2026

Pfizer on June 6 presented detailed Phase 2b results for berobenatide, an investigational injectable GLP-1 receptor agonist the company says could become the first approved monthly GLP-1 peptide, during a late-breaking symposium at the 86th Scientific Sessions of the American Diabetes Association ^[1]. The company also said it plans to run 10 Phase 3 studies of the drug in 2026 as part of a broader program of more than 20 obesity trials ^[1].

The headline number came from a 32-week exploratory extension (Part B) of the Phase 2b VESPER-1 study. Participants with obesity or overweight who moved from placebo to 2.4 mg weekly berobenatide lost 15.9% of their body weight, a figure that is not adjusted for placebo, with no plateau observed at 32 weeks — week 60 of the overall study ^[1]. Pfizer called this the first clinical experience with the top weekly dose ^[1].

A second study, VESPER-2, tested weekly dosing in adults with obesity or overweight who also had type 2 diabetes. Pfizer reported dose-dependent drops in both body weight and HbA1c, a blood sugar measure. At the 1.6 mg weekly dose, HbA1c fell 2.2% at week 28 using an on-treatment efficacy analysis, compared with a 0.2% reduction on placebo ^[1][2].

Pfizer also re-presented detail from VESPER-3, an ongoing 64-week study of monthly maintenance dosing in people with obesity or overweight without type 2 diabetes ^[1]. That trial randomized roughly 250 adults and previously showed placebo-adjusted weight loss of 10% and 12.3% at week 28 on the low and medium monthly regimens Pfizer is carrying into Phase 3 ^[2]. Across the program, the company said tolerability was favorable, with low rates of gastrointestinal side effects and discontinuations despite rapid dose escalation and no allowed step-down, and pointed to a 0.5 mL injection volume as a convenience advantage ^[1].

"In Phase 2b studies, berobenatide delivered continuous, uninterrupted weight loss at all doses selected for Phase 3, while preserving a tolerable profile as people transitioned from a weekly to a monthly maintenance dose," said Jim List, MD, PhD, Pfizer's chief internal medicine officer ^[1][2].

Why it matters for patients

Every GLP-1 medicine on the US market for weight is taken at least weekly, or daily in the case of oral Rybelsus. A once-monthly injection would mean 12 shots a year instead of 52. Pfizer frames that as a durability and adherence question, and outside commentary at the meeting echoed it. "Weight management is a lifelong commitment, and the barriers to staying on therapy long-term are just as important as the therapy itself," said John B. Buse, MD, PhD, of the University of North Carolina School of Medicine ^[1].

How berobenatide compares with drugs already on pharmacy shelves is unsettled. Fierce Biotech noted that tirzepatide (Zepbound) showed 20.9% weight loss at 72 weeks in a late-stage trial, and the high dose of semaglutide (Wegovy) showed 18.7% at the same time point — but these are longer trials, and cross-trial comparisons carry inherent flaws ^[2]. Berobenatide's 15.9% figure covers 32 weeks of extension dosing and is not placebo-adjusted ^[1], so it is not an apples-to-apples match.

It is also worth noting what is not yet known. The sources do not give a filing or approval date for berobenatide, do not break out specific rates of nausea, vomiting or other side effects, and do not report how much lean versus fat mass was lost. Safety and efficacy in larger, longer Phase 3 populations have not been reported.

What happens next

Three Phase 3 studies are already underway or open. VESPER-4 is testing once-weekly berobenatide in adults with obesity or overweight without type 2 diabetes; VESPER-5 is testing it in adults who also have type 2 diabetes, including a higher 2.4 mg weekly dose; and VESPER-6, the pivotal once-monthly study, is now open for enrollment ^[1][2]. Seven more Phase 3 studies are planned, aimed at obesity-related conditions including knee osteoarthritis and obstructive sleep apnea ^[1].

Pfizer is also running SOLIS-1, a Phase 2b study of an ultra-long-acting amylin analog (PF'3945) alone and combined with berobenatide ^[1]. The company acquired berobenatide, previously coded MET-097i, through its $10 billion purchase of Metsera, and in February paid $495 million for US-facing commercialization rights to Sciwind Biosciences' GLP-1 ecnoglutide ^[2].