Regeneron pushes back the readout on its muscle-preservation combination

Regeneron's Phase 2 study of trevogrumab, given alone or with garetosmab on top of semaglutide, has a new primary completion date of June 16, 2026, moved from May 6, 2026, according to a registry update tracked by GLP-1 Briefing.^[1] The trial is testing whether these antibodies can help people lose weight and fat while keeping more of their muscle than semaglutide alone would allow.

The change is a scheduling delay, not a result. It is one of 147 changes to GLP-1 trial records that outside monitors have logged since late August 2026, and one of only four flagged as a "lead" change because it involves a meaningful shift in timing.^[1] The source note that ClinicalTrials.gov overwrites old values when a trial record changes, so a delay like this would otherwise leave no public trace.^[1]

Regeneron's earlier COURAGE data, reported in September 2025, found that trevogrumab roughly halved the lean-mass loss normally seen with semaglutide, and that adding garetosmab cut it further, down to about 7.4% of total weight lost coming from lean mass.^[2] For comparison, in a separate body-composition study of tirzepatide, roughly 25% of weight lost was lean mass, a ratio that held even in the placebo group, suggesting the loss is a normal part of losing a large amount of weight by any method, not something unique to GLP-1 drugs.^[2] Semaglutide studies have generally shown a somewhat larger share, with lean mass making up an estimated 35% to 40% of weight lost.^[2]

Regeneron is not alone in this effort. More than a dozen companies are now developing drugs meant to be paired with GLP-1 medicines to protect muscle, including bimagrumab, which in a 507-person Phase 2 trial called BELIEVE cut lean-mass loss from 6.9% down to 2.3% at 48 weeks while total weight loss rose to 16.4%, and apitegromab, which preserved 1.9 kg more lean mass than placebo when added to tirzepatide.^[2] None of these combinations is approved by the FDA for any use, and the field carries real uncertainty. Eli Lilly ended one bimagrumab trial in September 2025 for business reasons, and the FDA now appears to require that any add-on drug show extra weight loss beyond a GLP-1 alone, not just a better ratio of fat to muscle lost.^[2]

Why it matters for patients

For people currently taking semaglutide or tirzepatide, this news does not change anything about their treatment today. None of these muscle-preserving combinations is approved, and the earliest Regeneron could report results from this specific trial is now mid-June 2026 at the soonest, based on the registry's new completion date.^[1]

The bigger picture matters more than the date itself. Losing lean mass along with fat is a known and expected part of losing significant weight, whether through diet, surgery, or a GLP-1 drug.^[2] Bariatric surgery patients lose an average of 8.13 kg of lean mass in the first year, a similar pattern to what shows up on GLP-1 drugs.^[2] The two interventions with the strongest evidence for keeping more muscle during weight loss remain unglamorous: getting roughly 1.2 to 1.6 grams of protein per kilogram of body weight each day, and resistance training at least three times a week combined with regular aerobic activity.^[2] A 2021 trial found that combining exercise with liraglutide produced more weight loss and preserved more lean mass than either approach alone.^[2]

What happens next

Regeneron's trevogrumab and garetosmab study is now expected to reach its primary completion around June 16, 2026, according to the current registry listing, though that date has already moved once and could shift again.^[1] Other muscle-preservation programs, including bimagrumab and apitegromab, are also generating data on separate timelines, and none of these drugs has a clear path to FDA approval yet.^[2]