Pfizer starts the first of its September berobenatide Phase 3 trials

Pfizer has registered a new round of Phase 3 trials for berobenatide (PF-08653944), an experimental once-monthly injectable for obesity, including a US study called VESPER-6 and companion trials in Japan and China ^[1][2].

VESPER-6, listed on ClinicalTrials.gov under the identifier NCT07595549, is described as a study to learn about berobenatide in people with overweight or obesity ^[1]. In Japan, Pfizer has registered two related studies: VESPER-JM, a once-monthly trial expected to enroll about 197 adults with obesity, some of whom may also have type 2 diabetes, with a start date of September 27, 2026, and VESPER-JW, a once-weekly version of the same design expected to enroll about 180 adults, also starting September 27, 2026 ^[2]. A separate Phase 3 study in China will test once-weekly berobenatide in Chinese adults with overweight or obesity, with a start date of August 31, 2026 ^[2]. All of these studies are randomized, double-blind, and placebo-controlled, and all involve injections under the skin of the abdomen ^[2].

Berobenatide is a synthetic peptide that acts on the GLP-1 receptor, the same target used by semaglutide and tirzepatide ^[2]. It was originally developed by D&D Pharmatech and later Metsera before Pfizer took over the program ^[2]. Pfizer's chief scientific officer, Chris Boshoff, told investors in early August 2026 that an internal analysis suggests berobenatide can deliver weight loss comparable to tirzepatide and potentially better than semaglutide, a claim he based partly on results from the extension arm of berobenatide's Phase 2b VESPER-1 trial ^[2]. Boshoff said the company is increasingly confident the drug could offer strong weight-loss results with tolerable gastrointestinal side effects and the convenience of monthly dosing ^[2].

The new trials come as Pfizer has narrowed its broader obesity pipeline. In the same early-August update, the company disclosed it was discontinuing two other obesity-related programs: an oral GLP-1 candidate called MET-224o, which also came from the Metsera deal, and a GIPR antagonist, PF-07976016, after reviewing mid-stage data ^[2]. Pfizer said it remains committed to exploring other oral GLP-1 approaches but that berobenatide is now the lead asset in its injectable obesity pipeline ^[2]. A count on the drug's development record lists 16 registered clinical trials tied to berobenatide as of early September 2026 ^[2].

Why it matters for patients

Berobenatide is not approved for use in the United States, and none of the trials described here have reported results yet. For patients currently weighing GLP-1 options, this news signals that a monthly-dosing alternative to weekly injections like Ozempic, Wegovy, and Zepbound is moving through formal testing, but it is not something anyone can access outside a clinical trial right now. The comparison Pfizer's Boshoff drew to tirzepatide and semaglutide is based on the company's own analysis and extension-arm data from an earlier trial, not from a completed head-to-head Phase 3 study, so it should be read as an early signal rather than a settled finding ^[2]. The different dosing schedules being tested in Japan, monthly versus weekly, also show that even within Pfizer's own program, the ideal dosing interval is still being worked out ^[2].

What happens next

The China trial is set to begin August 31, 2026, and the two Japan trials on September 27, 2026 ^[2]. The US-based VESPER-6 study is also underway ^[1]. Results from these Phase 3 trials, along with additional studies expected to follow, will take time to mature given the multi-visit, months-long design described for the Japan trials, which run roughly 21 to 22 months per participant ^[2]. It is not yet known from the available trial records exactly when full results or a US regulatory filing might be expected.