Pfizer’s recently acquired weight loss injection has shown to maintain weight loss after a switch from weekly to monthly dosing in a Phase IIb trial, suggesting the drugmaker’s $10bn bet on Metsera looks well placed.
In the VESPER-3 study (NCT06973720), the monthly maintenance glucagon-like peptide-1 receptor agonist (GLP-1RA) PF’3944, previously MET-097i, was investigated in adults with obesity or overweight without type 2 diabetes.
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The study found that PF’3944 achieved continued weight loss when switching from weekly to monthly subcutaneous injections, with efficacy being maintained. Dosing was reduced from a weekly to a monthly basis after 12 weeks.
The study demonstrated statistically significant weight reduction of 10% and 12.3% mean placebo-adjusted weight loss at week 28 from cohort one and cohort two. The lack of plateau at week 28 suggests continued weight loss is expected as the study continues through week 64.
The doses from cohorts one and three, low and medium monthly maintenance dosing regimens, are planned for inclusion in Phase III.
Detailed results from VESPER-3 will be presented on 6 June 2026, at the 86th Scientific Sessions of the American Diabetes Association (ADA).
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By GlobalDataPF’3944 also maintained a well-tolerated and favourable safety profile through week 28 that is consistent with the GLP-1RA class.
Dr Jim List, chief internal medicine officer of Pfizer, said: “These topline results from the Phase IIb VESPER-3 study reinforce the potential of PF’3944 as a monthly treatment with competitive efficacy. 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 III.”
Metsera agreement added PF’3944 to Pfizer portfolio
In November 2025, Pfizer acquired Metsera after becoming embroiled with Novo Nordisk in a bidding war. Pfizer eventually won with a $10bn offer for the obesity biotech. Upon the acquisition, Pfizer took charge of the development of MET-097i, now called PF’3944, including the ongoing, 64-week, randomised, double-blind, placebo-controlled VESPER-3 study.
Interim tolerability results from the VESPER-3 trial were previously reported after 12 weeks of weekly dosing by Metsera in September 2025. These data found that therapy was well tolerated with minimal diarrhoea signal and a risk difference from placebo of 13% nausea and 11% vomiting at 12 weeks after two titration steps.
Pfizer is set to run a large number of Phase III trials of PF’3944, including the recently initiated VESPER-4 pivotal study (NCT07311850) investigating once-weekly PF’3944 in patients who are overweight or with obesity and without type 2 diabetes.
The company has also planned the VESPER-5 study investigating once-weekly PF’3944 patients who are overweight or with obesity with type 2 diabetes, and the VESPER-6 study with once-monthly PF’3944 in patients who are overweight or with obesity. It will also initiate at least seven additional planned Phase III studies of PF’3944 designed to target comorbidities and increase patient optionality and access.
Pfizer has further obesity assets in development as part of an exclusive global collaboration and license agreement with YaoPharma.
Pfizer is hoping to pit itself against obesity giants Novo Nordisk and Eli Lilly. While Eli Lilly’s injectable GLP-1RA has shown higher sales in 2025, Novo Nordisk has taken the lead in the oral market after its oral version of semaglutide gained US Food and Drug Administration (FDA) approval in December 2025.
Novo Nordisk has also released data from a Phase III trial of CagriSema, a combination of cagrilintide and semaglutide, in which it outperformed Ozempic (semaglutide) in patients with type 2 diabetes.
