The Monthly Weight-Loss Shot That Hasn't Peaked Yet

Pfizer's monthly GLP-1 shot hit its Phase 2b weight loss target at 28 weeks, with no plateau in sight

10 Apr 2026

A once-a-month obesity injection may be about to shake up a market that weekly shots currently dominate. Pfizer's Phase 2b data on PF-3944 show the ultra-long-acting GLP-1 drug is working, still improving, and built for the long haul.

Topline results from the VESPER-3 trial, released February 3, 2026, confirmed PF-3944 met its primary endpoint of statistically significant weight reduction at 28 weeks across all four dose arms. The two groups advancing to Phase 3 achieved 10% and 12.3% placebo-adjusted weight loss. No plateau had appeared by week 28, suggesting further reductions as the 64-week study runs its course.

Enrolled participants were adults living with obesity or overweight but without type 2 diabetes. The trial opened with 12 weeks of weekly titration before shifting to monthly injections, a sequence designed to test whether the drug could hold its gains at lower dosing frequency. It did. Side effects were mild and mostly gastrointestinal, consistent with the GLP-1 drug class, and few participants dropped out due to adverse events.

Jim List, MD, PhD, Pfizer's Chief Internal Medicine Officer, said the data reinforced confidence in PF-3944 as a competitive monthly option and confirmed a higher maintenance dose would be included in Phase 3.

Pfizer is not betting on a single horse. Following its acquisition of Metsera and a collaboration with YaoPharma, the company has more than 20 obesity trials running in 2026, including 10 Phase 3 studies of PF-3944 across obesity, type 2 diabetes, and cardiovascular comorbidity indications.

Adherence is where weekly regimens quietly lose patients, and monthly dosing addresses that directly. A credible once-monthly option could bring more people into sustained treatment and keep them there. Full VESPER-3 results are set for the American Diabetes Association Scientific Sessions in June 2026, where the data will face its first serious peer scrutiny.

The race to own long-term obesity care just got more interesting.