The drugs designed to stop you losing muscle on GLP-1s

TL;DR

• Trial data put up to 40% of GLP-1 weight loss in lean mass - but a 2026 real-world cohort (n=486) found 80–85% of the loss was fat, with relative muscle mass preserved or increased in over 70% of patients.
• Bimagrumab plus semaglutide reached about 22% weight loss at 72 weeks in the Phase 2 BELIEVE trial, ~92% of it fat, with lean-mass loss ~2.9% versus ~7.4% on semaglutide alone.
• Trevogrumab, an anti-myostatin antibody, preserved lean mass added to semaglutide in the COURAGE Phase 2 trial, where ~35% of the weight lost was otherwise lean.
• Enobosarm cut lean-mass loss to about 1.2% versus about 4.1% on semaglutide alone in the QUALITY trial in adults 60+, and is advancing to Phase 3.
• Every drug named here is investigational - bimagrumab and trevogrumab are Phase 2, none is approved, none is available.
• The proven answer available today is resistance training plus adequate protein - in the S-LITE trial, a GLP-1 with supervised training increased lean mass rather than merely holding it.

Educational content, not medical advice. No doses or protocols appear. Bimagrumab and trevogrumab are investigational (Phase 2).

Updated 13 September 2026: gives the QUALITY trial (enobosarm added to semaglutide in adults 60+) its own entry with the lean-mass figures and its progression to Phase 3 - it was previously buried in an "others in development" list with no data attached. BELIEVE remains correctly labelled Phase 2.

Updated September 2026: qualifies the "up to 40%" premise. A 2026 real-world cohort (n=486) found 80-85% of weight lost was fat mass and relative skeletal muscle mass was preserved or increased in more than 70% of patients, so muscle loss is not the default outcome the muscle-preservation category is often marketed against.

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GLP-1 drugs are superb at removing weight - but not all of that weight is fat. Trial data show up to 40% of GLP-1 weight loss can be lean mass (muscle and connective tissue), and losing muscle is a problem: it lowers your resting metabolism, hurts physical function, and makes weight re-gain easier.

One correction before going further, because it changes how you should read the rest of this page. That "up to 40%" is the top of a trial-derived range, and a 2026 real-world retrospective cohort - 486 adults at a specialist obesity clinic in Vienna, 2022–2025 - reported a considerably less alarming picture: 80–85% of the weight lost was fat mass, mean skeletal muscle loss was around 5%, and relative skeletal muscle mass was preserved or increased in more than 70% of patients. That is a single-centre, non-randomised cohort in a supervised setting, and it should be weighed as such. But it matters here specifically: a drug class whose commercial premise is "GLP-1s destroy your muscle" is being built against a problem that, for most supervised patients, appears to be smaller than advertised. Read the pipeline below with that in mind. Fuller treatment in GLP-1s and muscle loss. Two responses are emerging. The proven one, available now, is resistance training plus adequate protein. The future one is a new class of drugs - bimagrumab, trevogrumab and relatives - that in early trials preserve or even build muscle while GLP-1s strip fat. Here's the honest split between what works today and what's coming.

First - what actually works now

Before any new drug, the evidence-backed way to protect muscle on a GLP-1 is unglamorous and effective:

• Resistance training - the single strongest signal to keep muscle during weight loss. In the S-LITE trial, combining a GLP-1 with supervised training didn't just preserve lean mass - patients gained it, an outcome drugs alone didn't match.
• Protein - roughly 1.2–1.6 g/kg/day supports lean-mass retention, with diminishing returns above that.

This is the foundation, and it's why losing fat, not muscle, on a GLP-1 is a training-and-nutrition problem first, a pharmacology problem second.

The new drug class: preserving muscle pharmacologically

The emerging drugs work on the activin/myostatin system - biological "brakes" on muscle growth. Block them, and the body holds (or adds) muscle while fat comes off:

• Bimagrumab - a monoclonal antibody against type II activin receptors. In the BELIEVE Phase 2 trial (published in Nature Medicine, 2026), bimagrumab combined with semaglutide produced about 22% weight loss at 72 weeks with ~92% of it from fat - lean-mass loss was only ~2.9%, versus ~7.4% with semaglutide alone. Bimagrumab alone caused weight loss that was 100% fat, with a 2.5% increase in lean mass. It's now being studied with tirzepatide too.
• Trevogrumab - an anti-myostatin antibody (Regeneron). In the COURAGE Phase 2 trial, adding trevogrumab (with or without the anti-activin-A antibody garetosmab) to semaglutide preserved lean mass and increased fat loss - against a backdrop where ~35% of semaglutide's weight loss was otherwise lean mass. The triple combination had more tolerability issues.
• Enobosarm - an oral selective androgen receptor modulator (SARM), and the one non-antibody entrant with its own named readout. In the QUALITY trial, adding enobosarm to semaglutide in adults aged 60 and over cut lean-mass loss to about 1.2%, versus about 4.1% on semaglutide alone, with physical function also better preserved. It is advancing to Phase 3. Worth separating from the activin/myostatin antibodies above: different mechanism, different regulatory history, and a compound class with a long record of unsupervised misuse outside trials.
• Others in development - garetosmab and apitegromab, both at earlier stages.

The honest caveats

• All investigational. Bimagrumab and trevogrumab are Phase 2; enobosarm is entering Phase 3. None is approved, none is available. The numbers are promising but early, and a Phase 2 result is a reason to run Phase 3, not a reason to act.
• Function still needs proving. Preserving lean mass on a scan isn't the same as preserving strength and function; those endpoints remain sparse.
• Not a substitute for the basics. Even if these drugs arrive, training and protein will remain the foundation - and they're free, available, and health-promoting on every other axis.

The bottom line - and where to start

Muscle loss is the real weakness of GLP-1 weight loss, and the field is moving fast to address it: bimagrumab and trevogrumab preserve or add muscle while fat falls in Phase 2 trials - genuinely exciting, but investigational and years out. What you can do now is proven and powerful: resistance training and adequate protein, ideally within a supervised plan that tracks body composition, not just the scale. That's how you make sure the weight you lose is the weight you want to lose.

Explore it with verified supply. Every Vivre Labs lot is independently tested and the certificate of analysis is published, so you know exactly what is in the vial. Explore semaglutide.

Frequently asked questions

How much muscle do you lose on Ozempic or Mounjaro? Studies suggest up to 40% of GLP-1 weight loss can be lean mass (around 35% in some trials), though resistance training and adequate protein substantially reduce that. Losing muscle lowers resting metabolism and makes regain easier.

What is bimagrumab? An investigational monoclonal antibody that blocks activin receptors to preserve or build muscle. In a Phase 2 trial with semaglutide, ~92% of weight loss came from fat and lean-mass loss was minimal. It's not yet approved.

Can I preserve muscle on a GLP-1 without new drugs? Yes - resistance training plus about 1.2–1.6 g/kg/day of protein is the proven approach available now, and combining training with a GLP-1 has even increased lean mass in trials.

Related reading

• Losing fat, not muscle, on a GLP-1 · New weight-loss drugs 2026–2027 · Do GLP-1s work differently in women and men?
• Part of The Complete Guide to GLP-1s

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Educational content, not medical advice. Bimagrumab and trevogrumab are investigational (Phase 2); trial data and timelines change. Claims for the Malaysian market are subject to MAB requirements.

References

• Heymsfield SB, et al. Bimagrumab plus semaglutide alone or in combination for the treatment of obesity: a randomized phase 2 trial (BELIEVE). Nature Medicine. 2026. (~22% weight loss at 72 wks, ~92% from fat; lean-mass loss ~2.9% vs ~7.4% semaglutide alone; bimagrumab alone +2.5% lean mass) · Regeneron COURAGE Phase 2 (trevogrumab ± garetosmab + semaglutide): ~35% of semaglutide weight loss was lean mass; combinations preserved lean mass. · S-LITE trial: GLP-1 + supervised resistance/aerobic training preserved/increased lean mass; protein ~1.2–1.6 g/kg/day. · QUALITY trial (enobosarm + semaglutide, adults 60+): lean-mass loss ~1.2% vs ~4.1% with semaglutide alone; advancing to Phase 3. · Activin/myostatin inhibitors (bimagrumab, trevogrumab, garetosmab, apitegromab) and SARM enobosarm - all investigational; none approved for this use.