Regeneron pushes back Phase 2 completion date for trevogrumab muscle study

Regeneron has pushed back the primary completion date for a Phase 2 trial that adds its experimental drug trevogrumab — alone or combined with a second drug, garetosmab — to semaglutide, according to a registry change logged by a trial tracker ^[1]. The primary completion date moved from May 6, 2026 to June 16, 2026, about six weeks later ^[1].

The trial is testing whether the combination shifts the mix of what participants lose, aiming for more fat loss and less lean-tissue loss. Regeneron reported earlier COURAGE results in September 2025: trevogrumab roughly halved the lean-mass loss caused by semaglutide, and adding garetosmab cut it further, to 7.4% of total weight lost ^[2].

Changes like this are easy to miss because ClinicalTrials.gov overwrites a record when it is updated and keeps no public history of the old value ^[1]. The tracker that recorded this change snapshots the registry six times a day and has logged 147 changes since monitoring began on Aug. 21, 2026, across 122 trials ^[1].

Regeneron is one of several companies testing drugs meant to protect lean mass in people taking GLP-1s. None is FDA-approved for that purpose ^[2]. In the BELIEVE Phase 2 trial, which enrolled 507 participants and was published in Nature Medicine in 2026, semaglutide alone produced a 6.9% drop in lean mass at week 48; with the drug bimagrumab added, lean mass fell 2.3% while total weight loss rose to 16.4%, with 92.3% of that loss coming from fat ^[2]. Reported trade-offs included muscle spasms, diarrhea, acne, a 17.6% rise in LDL cholesterol on bimagrumab alone, and discontinuation for side effects in 14% to 21% of participants ^[2].

A separate program, apitegromab (EMBRAZE, Nature Medicine, 2026), preserved 1.9 kg more lean mass than placebo alongside tirzepatide ^[2]. Lilly terminated one bimagrumab trial in September 2025 for business reasons, and the FDA now appears to require added weight loss over a GLP-1 alone as an endpoint, not just better body composition ^[2].

Some context on the problem: lean-mass loss accompanies large weight loss generally, not only GLP-1 use. In the SURMOUNT-1 DXA sub-study, which followed 160 participants over 72 weeks, tirzepatide produced 21.3% weight loss, with fat mass down 33.9% and lean mass down 10.9% — roughly 75% of the loss was fat and 25% was lean. The same ratio appeared in the placebo group ^[2]. In the STEP-1 DXA sub-study, total lean body mass fell 9.7% alongside a 15.0% weight loss; the figure often quoted is that 35% to 40% of the weight lost is lean mass ^[2]. "Lean mass" on a DXA scan includes body water, glycogen and organ mass, not only muscle ^[2].

Why it matters for patients

Timing is the practical consequence. Every delay pushes body-composition data further out, and people deciding about or already taking a GLP-1 have no approved drug option for protecting lean tissue during treatment ^[2].

The delay also matters because of how these results are being judged. A drug that preserves lean mass but does not add weight loss over a GLP-1 alone may not clear the bar the FDA appears to be setting, based on the Lilly termination and the endpoint shift ^[2]. So the details in the eventual readout — how much lean mass is preserved and whether total weight loss holds up — carry weight.

Comparing the programs is not yet possible. The reported lean-mass figures come from different trials with different designs, participant counts and durations, and no head-to-head data has been reported ^[2].

Add-ons sold online are a separate category. Peptides such as BPC-157, TB-500 and ipamorelin have no human efficacy data for preserving muscle on a GLP-1 ^[2]. In a 2026 analysis of 6,441 consumer-marketed peptide samples across 14 compounds, 41.6% to 71.1% failed basic quality criteria and 15% had measurable endotoxin contamination ^[2].

What happens next

The registry now lists June 16, 2026 as the primary completion date for the Regeneron trial ^[1]. That date marks the end of primary data collection, not the release of results. A date for reporting the Phase 2 results has not been reported.

Registry dates move often and in both directions. Among the 147 changes the tracker has recorded, some results dates moved months later and others moved more than two years earlier ^[1].