Pfizer has released mid-stage (Phase 2b) VESPER-3 results: its experimental drug PF’3944 (previously known as MET-097i and brought into Pfizer via the Metsera deal) helped people with obesity or overweight lose up to 12.3% of body weight (placebo-adjusted) by week 28. The headline feature is the dosing schedule: patients started with weekly injections during dose escalation, then switched to a once-monthly maintenance shot. Pfizer says there was no clear weight-loss “plateau” by week 28, and the trial continues through week 64.
A key nuance: Pfizer is reporting placebo-adjusted weight loss (the difference between the drug group and the placebo group). That’s the standard way clinical trials talk about results, but it’s not the same as the everyday “I lost X% of my weight.” And these are week-28 numbers — not a full-year readout. Meanwhile, investors have gotten used to eye-popping efficacy from the leaders in the category, which is why the reaction is basically: “Nice… but is it competitive?”
Pfizer’s communications also point to side effects and to some patients stopping treatment. In VESPER-3, a number of participants discontinued because of adverse events during both the weekly and monthly phases. For GLP-1 drugs, gastrointestinal issues (nausea, diarrhea, etc.) are common — and in the real world, tolerability often determines whether people stay on therapy long enough to see meaningful results.
So what’s next? Pfizer is essentially trying to make long-term treatment easier to live with: one shot a month instead of one a week. In its official materials, the company discusses moving the program forward (including later-stage development) and dialing in dosing strategy, including modeling a higher dose in future studies. If things go as planned, Pfizer is aiming for a potential launch closer to 2028.
Worth keeping expectations calibrated: these are topline results and corporate communications (a press release and investor-oriented commentary), not a full peer-reviewed journal paper with deep detail on body composition, metabolic markers, subgroup breakdowns, and so on. Still, having an official press release and a clear trial design makes the story more solid than the usual hype cycle.