Pharma powerhouse Pfizer has announced that its investigational obesity treatment delivered significant weight loss in the Phase 2b VESPER-3 study, supporting the potential for monthly dosing in adults with overweight or obesity without type 2 diabetes.
The study tested whether PF’3944 could maintain efficacy when switching from weekly to monthly injections and remain safe and well-tolerated. Results showed up to 12.3% mean placebo-adjusted weight loss at week 28, with all four dosing regimens outperforming placebo.
“This topline results from the Phase 2b VESPER-3 study reinforce the potential of PF’3944 as a monthly treatment with competitive efficacy,” said Jim List, Chief Internal Medicine Officer.
“Based on the monthly dosing efficacy and tolerability demonstrated in this trial, we remain confident in our plan to include a higher 9.6 mg monthly maintenance dose of PF’3944 in Phase 3. With PF’3944 as an anchor of Pfizer’s obesity pipeline, we are positioned to address critical gaps in obesity care and meet the diverse needs of patients.”
VESPER-3 is a 64-week, randomized, double-blind, placebo-controlled study evaluating weekly-to-monthly dosing of PF’3944 across four titration protocols. In the low and medium monthly dose arms, participants achieved 10% and 12.3% placebo-adjusted weight loss, with no plateau by week 28—suggesting ongoing weight loss through the study’s completion at week 64.
PF’3944’s safety profile remained favorable. Gastrointestinal side effects were mostly mild or moderate, with no severe diarrhea and only rare instances of severe nausea or vomiting. Across key study arms, ten participants discontinued due to adverse events, while none discontinued in the placebo group.
Pfizer is rapidly advancing its obesity pipeline following the acquisition of Metsera and a global collaboration with YaoPharma. The company plans over 20 clinical trials in 2026, including at least 10 Phase 3 trials of PF’3944, spanning weekly and monthly dosing, type 2 diabetes and non-diabetes populations, and studies targeting obesity-related comorbidities.
