Global pharma giant Pfizer is moving aggressively into the next wave of obesity treatment.

 

The company has reported robust Phase 2b results for its experimental GLP-1 receptor agonist berobenatide (PF-3944), a drug designed for monthly dosing that could reshape long-term weight management if it succeeds in late-stage trials.

 

The company said data from multiple VESPER studies show the peptide delivered meaningful weight loss, favorable tolerability, and the possibility of a first-in-class monthly injection format—an approach aimed at improving adherence in chronic obesity care.

 

Across the Phase 2b VESPER-1, VESPER-2, and VESPER-3 trials, Pfizer said the drug demonstrated “proof of concept for berobenatide as a potential first-in-class monthly GLP-1 RA peptide that can deliver competitive weight loss,” along with “favorable tolerability…"

 

The most closely watched data came from an extension of the VESPER-1 study, where patients who escalated from placebo to 2.4 mg weekly berobenatide achieved a non-placebo-adjusted weight loss of 15.9% over 32 weeks, with researchers reporting no observed plateau at 32 weeks.

 

That result strengthens the case for sustained efficacy over time, a key challenge in obesity pharmacotherapy, where weight loss often levels off or reverses.

 

Pfizer is now preparing a major late-stage push. It plans to launch 10 Phase 3 trials in 2026, spanning chronic weight management and obesity-related conditions including knee osteoarthritis and obstructive sleep apnea. The broader program will ultimately include more than 20 obesity-related studies.

 

In Phase 2b VESPER-2, which included participants with type 2 diabetes, the drug showed dose-dependent improvements in both weight and blood sugar control. At week 28, the highest weekly dose produced a 2.2% reduction in HbA1c, compared with 0.2% in the placebo group, underscoring its metabolic impact beyond weight loss.

 

Executives say the data support both weekly and monthly dosing strategies as Pfizer advances into Phase 3.

 

“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, Chief Internal Medicine Officer, Pfizer. 

 

“These data highlight the potential for berobenatide to be the first approved monthly GLP-1 RA peptide and support our extensive Phase 3 program that includes 10 studies for chronic weight management and obesity-related comorbidities. 

 

"With berobenatide as a potential foundational metabolic medicine, both as a single agent and as a combination backbone, Pfizer is advancing a differentiated pipeline with multiple mechanisms and modalities designed to meet the many needs of people living with obesity and related conditions.”

 

Outside experts also pointed to the clinical relevance of switching from weekly to monthly dosing, a shift that could improve long-term adherence if the drug reaches market.

 

“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, Professor of Medicine at the University of North Carolina School of Medicine, Chapel Hill. 

 

“The growing body of evidence shows berobenatide delivering meaningful weight loss with a well-tolerated profile following a switch from weekly to monthly dosing in Phase 2b studies. If approved, berobenatide has the potential to not only be effective, but practical and sustainable in real life.”

 

Pfizer is also testing combination strategies, including pairing berobenatide with an ultra-long-acting amylin analog in a separate Phase 2b program.

 

With obesity rates projected to rise globally into the billions over the coming decade, Pfizer is positioning berobenatide as a potential cornerstone therapy in a rapidly expanding metabolic drug market—one increasingly defined by high efficacy, long-acting formulations, and combination regimens.