Pfizer files Phase 3 trial of once-monthly berobenatide in Japan
Pfizer's experimental obesity shot berobenatide is moving into late-stage testing in Japan, but it is not approved anywhere and no Phase 3 weight-loss results have been reported yet.
Pfizer has filed a Phase 3 trial of its once-monthly obesity drug berobenatide in Japan. The study, called VESPER-JM, is listed with a start date of Sept. 27, 2026 [1]. A companion Japanese trial is testing a once-weekly version of the same drug [1].
The two Japanese studies
VESPER-JM (NCT07794774) is a randomized, double-blind, placebo-controlled Phase 3 study of once-monthly berobenatide in adults in Japan with obesity disease — a term used there for obesity as a medical condition in which a person has too much body fat, which can harm health and raise the risk of other medical problems [1]. Some participants may also have type 2 diabetes [1].
About 197 adults will take part. They will be assigned by chance to receive berobenatide or a placebo, given as an injection under the skin of the abdomen [1]. People take part for about 21 months, with about 16 visits at the study site and two phone visits [1].
The companion study, VESPER-JW (NCT07794761), tests once-weekly berobenatide in about 180 adults with obesity disease in Japan, some of whom may also have type 2 diabetes [1]. Participants take part for about 22 months, with about 15 site visits and two phone visits [1]. That study was first submitted Aug. 26, 2026 and last updated Sept. 3, 2026, and is not yet recruiting [2]. It uses a parallel-group design and triple blinding, meaning participants, care teams and investigators do not know who receives the active drug [2]. Both Japanese listings show a status of not yet recruiting [1].
Pfizer is also running a Phase 3 study of once-weekly PF-08653944 — another name for berobenatide — in Chinese adults with overweight or obesity, listed with a start date of Aug. 31, 2026 [1].
What the drug is
Berobenatide is an injectable synthetic peptide that acts on the GLP-1 receptor [1]. It is also known as PF-08653944, PF'3944 and MET 097, and the drug database listing names D&D Pharmatech as the originator organization and Pfizer as an active organization [1]. Its listed highest phase is Phase 3, and the listing shows no first-approval date, meaning it is not approved in any country yet [1].
On Aug. 4, 2026, Pfizer Chief Scientific Officer Chris Boshoff said on the company's second-quarter earnings call that an analysis "suggests berobenatide can deliver weight loss comparable to tirzepatide and potentially better than semaglutide" [1]. Combined with data from the extension arm of the Phase 2b Vesper-1 trial, Boshoff said Pfizer is increasingly confident the drug "can potentially deliver robust efficacy and favorable [gastrointestinal] tolerability with the convenience of a monthly therapy" [1]. Those are company statements, not results from a Phase 3 trial.
The same update disclosed that Pfizer discontinued two other obesity programs: the oral GLP-1 drug MET-224o and the GIPR antagonist PF-07976016, which was dropped after Phase 2a data [1]. Pfizer continues to advance berobenatide as the lead asset in its obesity pipeline [1].
Why it matters for patients
Berobenatide is not available to patients in the United States or anywhere else. It has no approval date and remains in Phase 3 testing [1].
The practical question the drug raises is whether a once-monthly injection could eventually offer an alternative schedule to the weekly injections used by approved GLP-1 obesity medicines. Pfizer says monthly dosing may work, but no Phase 3 weight-loss results for berobenatide have been reported [1][2]. Whether monthly dosing produces weight loss and side effects similar to weekly dosing has not been established in a late-stage trial.
It is also not yet known whether Pfizer plans to run a Phase 3 obesity trial of berobenatide in the United States. That has not been disclosed in these listings [1][2].
No information on pricing, insurance coverage, or head-to-head comparisons with approved obesity drugs has been reported [1][2]. Berobenatide is a different molecule from semaglutide (sold as Ozempic, Wegovy and Rybelsus) and tirzepatide (sold as Mounjaro and Zepbound); the comparison to those drugs comes from Pfizer's own analysis, not from a completed Phase 3 study [1].
What happens next
- Aug. 31, 2026: listed start date for the Phase 3 study of once-weekly berobenatide in Chinese adults with overweight or obesity [1].
- Sept. 27, 2026: listed start dates for VESPER-JM and VESPER-JW, the two Japanese Phase 3 studies [1].
- Both Japanese trials list themselves as not yet recruiting, and participants stay on treatment and follow-up for about 21 to 22 months [1]. One report says topline data are several years away even as the program moves into its pivotal stage [2].
Sources
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