Pfizer files a Japanese Phase 3 of monthly berobenatide

Pfizer has submitted a Phase 3 study called VESPER-JM to test once-monthly berobenatide in Japanese adults with obesity, with a planned start date of September 27, 2026 ^[1]. The trial will enroll about 197 adults, some of whom may also have type 2 diabetes, and compare berobenatide against a placebo injected under the skin of the abdomen ^[1]. Participants are expected to stay in the study for about 21 months, including roughly 16 in-person visits and two phone check-ins ^[1].

The monthly study follows a companion trial, VESPER-JW, which tests a once-weekly version of the same drug in about 180 Japanese adults over roughly 22 months ^[1][2]. VESPER-JW was first submitted on August 26, 2026, and as of early September was listed as not yet recruiting ^[2]. Pfizer is also running a separate once-weekly Phase 3 trial of the drug in Chinese adults with overweight or obesity, which is set to start August 31, 2026 ^[1].

Berobenatide, also known as PF-08653944 or MET-097, is a GLP-1 receptor agonist that Pfizer picked up through its roughly $10 billion acquisition of Metsera ^[1]. On Pfizer's second-quarter 2026 earnings call, Chief Scientific Officer Chris Boshoff said an internal analysis "suggests berobenatide can deliver weight loss comparable to tirzepatide and potentially better than semaglutide," citing data from the extension arm of the drug's Phase 2b Vesper-1 trial ^[1]. Tirzepatide is sold as Mounjaro and Zepbound, and semaglutide is sold as Ozempic, Wegovy, and Rybelsus. Boshoff said Pfizer believes the drug could offer "robust efficacy and favorable gastrointestinal tolerability with the convenience of a monthly therapy" ^[1]. These are company statements based on internal analysis and an extension-trial comparison, not a head-to-head clinical trial result, so they should be read as preliminary.

The new Japanese filings came in the same period that Pfizer discontinued two other obesity-related programs: an oral GLP-1 drug called MET-224o, also inherited from Metsera, and a GIPR antagonist called PF-07976016 that had shown disappointing Phase 2a results when combined with liraglutide ^[1]. A Pfizer spokesperson said the company remains "committed to exploring oral peptide and small molecule approaches for agonism of the GLP-1 receptor" and still has one oral GLP-1 candidate, PF-08642534, licensed from China's YaoPharma ^[1].

Why it matters for patients

For people currently using or considering GLP-1 medications in the United States, this filing does not change anything about available treatment options today. Berobenatide is not approved anywhere, and these Phase 3 trials are enrolling only in Japan and China, not the United States ^[1][2]. If the once-monthly or once-weekly versions eventually reach the market, they would add another option to a field that already includes weekly semaglutide (Ozempic, Wegovy) and weekly tirzepatide (Mounjaro, Zepbound), potentially reducing how often patients need to inject.

The claim that berobenatide might match tirzepatide or beat semaglutide on weight loss comes from a company-reported comparison based on extension-study data, not a completed controlled trial testing the drugs directly against each other ^[1]. Independent, randomized head-to-head results are not yet available, so patients and clinicians cannot yet judge how the drug would actually compare in practice.

What happens next

VESPER-JM is expected to begin September 27, 2026, and VESPER-JW around the same date, with both Japanese trials expected to run for about 21 to 22 months from enrollment ^[1]. A companion once-weekly trial in Chinese adults is set to start August 31, 2026 ^[1]. Given those timelines, topline results from the Japanese pivotal program are not expected for at least a couple of years, and any path to U.S. availability would require additional trials and regulatory review after that.