Metsera’s New Obesity Data Raises Efficacy Profile, Key Side Effect Questions for Pfizer After Acquisition

Metsera’s lead obesity drug, MET-097i, demonstrated notable efficacy in a Phase 2 trial, achieving an average placebo-subtracted weight loss of 14–14.1% at the highest dose after 28 weeks, with individual responses up to 26.5%13.

A titrated (step-up) dosing regimen was shown to limit gastrointestinal side effects (notably nausea and vomiting) compared to the standard fixed-dose regimen, suggesting a potentially improved tolerability profile over current GLP-1-based therapies such as Eli Lilly’s Zepbound13.

Only 2 of 239 study participants discontinued the drug due to side effects in Metsera’s Phase 2 study, indicating a low dropout rate caused by tolerability issues1.

Reported side effects for titrated doses included nausea (13% higher than placebo), vomiting (11% higher), and minimal association with diarrhea. These rates are generally lower or comparable to leading competitors such as Zepbound13.

Metsera did not publicly release full safety data but emphasized minimal overall dropout due to adverse events. Ongoing studies will provide more robust safety and efficacy data by the end of 2025 or early 202613.

Pfizer acquired Metsera for $4.9 billion in September 2025. Pfizer aims to advance MET-097i into Phase 3 trials, striving to regain a leadership position in the highly competitive obesity drug market forecasted to reach $100 billion in annual sales13.

Pfizer has previously discontinued internal obesity programs due to safety concerns, increasing the need to carefully vet side effect profiles as new data emerges1.

There is no evidence from these trials or official releases suggesting unexpected or severe side effect concerns unique to MET-097i at this stage, but larger and longer-term studies are required for a definitive safety and efficacy assessment13.

Sources:

1. https://www.biopharmadive.com/news/metsera-obesity-drug-study-results-pfizer-deal/761462/

3. https://www.clinicaltrialsarena.com/news/pfizers-obesity-bet-shows-14-1-weight-loss-in-phase-iib-trial/