Pfizer Inc. (NYSE:PFE) said its investigational obesity drug PF-08653944 delivered placebo-adjusted weight loss of up to 12.3% in a phase 2b clinical study, supporting its potential as a monthly injectable treatment. The trial evaluated the GLP-1 receptor agonist in adults who were obese or overweight but did not have type 2 diabetes.
The phase 2b VESPER-3 study met its primary goal, showing statistically meaningful reductions in body weight at 28 weeks across all four dose levels tested versus placebo. Around 270 participants were enrolled and split evenly across five study groups, with roughly 54 individuals in each arm.
Patients began with weekly injections for the first 12 weeks before transitioning to a once-monthly dosing schedule through week 28. The two doses selected for late-stage development produced placebo-adjusted weight loss of 10% and 12.3%, respectively. Importantly, weight reduction continued after the switch to monthly dosing, with no evidence of a plateau by the end of the study period.
Pfizer said the treatment showed a safety and tolerability profile in line with other GLP-1 receptor agonists. Most gastrointestinal side effects were mild to moderate in severity, and five participants in each of the two key dose groups discontinued treatment because of adverse events during both the weekly and monthly dosing phases.
Looking ahead, Pfizer plans to launch 10 phase 3 trials of PF-08653944 in 2026, covering patient populations with and without type 2 diabetes. The compound was originally developed by Metsera, which Pfizer recently acquired, and the group also has a collaboration with YaoPharma as part of its broader obesity program.
More detailed findings from the ongoing 64-week study are expected to be presented at the American Diabetes Association Scientific Sessions in June 2026, according to a company statement.