Bimagrumab vs Ostarine
A monoclonal antibody and a SARM, both of which reliably add lean mass on a scan, and neither of which has ever improved what that mass is supposed to do.
Short answer
Bimagrumab and Ostarine both have human clinical data, so the deciding factor is what you want them for. Bimagrumab suits someone focused on obesity/body composition and muscle-wasting conditions, while Ostarine is aimed at muscle growth, recomposition and muscle preservation while cutting or on a GLP-1. Bimagrumab is given by IV infusion, while Ostarine is taken by mouth.
Bimagrumab
BYM338, LY3985863
A monoclonal antibody that reliably adds lean mass and strips fat across multiple randomized trials, but has never once improved a physical-performance outcome — not in inclusion body myositis (its pivotal RESILIENT trial failed), not in sarcopenia, not in COPD, not in obesity. It adds tissue that shows up on a scan; no trial has shown that tissue does more work.
Full Bimagrumab evidence reviewOstarine
Enobosarm, MK-2866, GTx-024
Reliably adds lean body mass and just as reliably fails to improve physical function — the two phase 3 POWER trials found both, which is why no regulator has ever approved it.
Full Ostarine evidence reviewBimagrumab vs Ostarine: head to head
- FDA status / approved use
Bimagrumab
Investigational antibody in phase 2 for obesity; not FDA-approved for any indicationOstarine
Never approved in any country; not a legal supplement ingredient; sold as a research chemical- Marketed for
Bimagrumab
Investigational for obesity/body composition and muscle-wasting conditions — no approved indicationOstarine
Muscle growth, recomposition, muscle preservation while cutting or on a GLP-1- Outcome areas
Bimagrumab
Muscle / strength / lean mass; Weight loss / appetiteOstarine
Muscle / strength / lean mass- Evidence grade
Bimagrumab
Clinical dataOstarine
Clinical data- How it works
Bimagrumab
Antibody blocking activin type II receptors, which restrain muscle growth and fat breakdownOstarine
Binds the androgen receptor, acting strongly in muscle and bone, weakly in prostate- Route and dosing
Bimagrumab
Intravenous infusion spaced weeks apart; subcutaneous dosing under studyOstarine
Oral, 3 mg daily in phase 3 trials- Headline human result
Bimagrumab
Combined with semaglutide, −17.8 kg at week 48 with 92% of weight lost as fat vs 71% on semaglutide alone (BELIEVE, 2026)Ostarine
Beat placebo on lean body mass but not physical function in two phase 3 trials of 651 lung cancer patients- Strongest evidence
Bimagrumab
RESILIENT phase 2/3, Lancet Neurol 2019Bimagrumab evidence reviewPubMed 31397289Ostarine
POWER phase 3 program, Lancet Oncol 2013Ostarine evidence reviewPubMed 23499390- Key safety signal
Bimagrumab
Muscle spasms, acne and raised LDL cholesterol; 14–21% discontinuation on monotherapyOstarine
Case reports of cholestatic liver injury; suppresses testosterone and lowers HDL cholesterol- How it is obtained
Bimagrumab
Legitimately available only inside clinical trialsOstarine
Sold gray-market as a research chemical; no approved human product
| Bimagrumab | Ostarine | |
|---|---|---|
| FDA status / approved use | Investigational antibody in phase 2 for obesity; not FDA-approved for any indication | Never approved in any country; not a legal supplement ingredient; sold as a research chemical |
| Marketed for | Investigational for obesity/body composition and muscle-wasting conditions — no approved indication | Muscle growth, recomposition, muscle preservation while cutting or on a GLP-1 |
| Outcome areas | Muscle / strength / lean mass; Weight loss / appetite | Muscle / strength / lean mass |
| Evidence grade | Clinical data | Clinical data |
| How it works | Antibody blocking activin type II receptors, which restrain muscle growth and fat breakdown | Binds the androgen receptor, acting strongly in muscle and bone, weakly in prostate |
| Route and dosing | Intravenous infusion spaced weeks apart; subcutaneous dosing under study | Oral, 3 mg daily in phase 3 trials |
| Headline human result | Combined with semaglutide, −17.8 kg at week 48 with 92% of weight lost as fat vs 71% on semaglutide alone (BELIEVE, 2026) | Beat placebo on lean body mass but not physical function in two phase 3 trials of 651 lung cancer patients |
| Strongest evidence | RESILIENT phase 2/3, Lancet Neurol 2019Bimagrumab evidence reviewPubMed 31397289 | POWER phase 3 program, Lancet Oncol 2013Ostarine evidence reviewPubMed 23499390 |
| Key safety signal | Muscle spasms, acne and raised LDL cholesterol; 14–21% discontinuation on monotherapy | Case reports of cholestatic liver injury; suppresses testosterone and lowers HDL cholesterol |
| How it is obtained | Legitimately available only inside clinical trials | Sold gray-market as a research chemical; no approved human product |
marks a row where the two differ. “Not established” marks a cell the available evidence does not answer. Evidence grades come from our evidence matrix, which grades each molecule on the human data for the use it is marketed for.
- Clinical data:
- Tested in humans — but investigational, discontinued, or proven only on a surrogate marker (not the marketed outcome).
Our verdict
This is the rare pair where both molecules share the same failure, and that shared failure is the most useful thing about comparing them. Bimagrumab consistently increases lean mass and strips fat — in BELIEVE at week 72 it cut fat mass 28.5% while adding 2.5% lean — yet across four randomized trials it has never improved a physical-performance outcome, and its pivotal RESILIENT trial in sporadic inclusion body myositis found no improvement in 6-minute walk distance at any dose. Ostarine’s phase 3 POWER program found precisely the same split: lean body mass rose and physical function did not, which is why no regulator has ever approved it. Neither is something a reader can obtain — bimagrumab is an infused antibody with no approved indication, and ostarine is not an approved medicine and is prohibited in sport. If either has a future it is probably alongside a GLP-1: BELIEVE tested bimagrumab with semaglutide and reported 92% of the weight lost coming from fat against 71% on semaglutide alone. That is still a body-composition endpoint, not a functional one.
Bimagrumab fits if
You are following the activin/myostatin pathway and want the better-documented trial record, including a real combination readout alongside a GLP-1.
Ostarine fits if
You want the SARM evidence stated honestly — that the lean-mass gains are real, and that the functional benefit has never materialised in a phase 3.
Bimagrumab vs Ostarine: common questions
- Is either bimagrumab or Ostarine FDA-approved?
- No. Bimagrumab is an investigational antibody in phase 2 for obesity; not FDA-approved for any indication. Ostarine has never been approved in any country; not a legal supplement ingredient; sold as a research chemical.
- Which has stronger human evidence, bimagrumab or Ostarine?
- Neither clearly. Both have human clinical data. The key source for bimagrumab is RESILIENT phase 2/3, Lancet Neurol 2019; for Ostarine, it is POWER phase 3 program, Lancet Oncol 2013.
- What are the main safety concerns with bimagrumab and Ostarine?
- For bimagrumab, watch for muscle spasms, acne and raised LDL cholesterol; 14–21% discontinuation on monotherapy. For Ostarine, watch for case reports of cholestatic liver injury; suppresses testosterone and lowers HDL cholesterol.
Key studies behind each
Bimagrumab
- Lach-Trifilieff E, Minetti GC, Sheppard K, et al. (2014). An antibody blocking activin type II receptors induces strong skeletal muscle hypertrophy and protects from atrophy. Mol Cell Biol. PubMed 24298022
- Hanna MG, Badrising UA, Benveniste O, et al.; RESILIENT Study Group. (2019). Safety and efficacy of intravenous bimagrumab in inclusion body myositis (RESILIENT): a randomised, double-blind, placebo-controlled phase 2b trial. Lancet Neurol. PubMed 31397289
- Amato AA, Hanna MG, Machado PM, et al.; RESILIENT Study Extension Group. (2021). Efficacy and Safety of Bimagrumab in Sporadic Inclusion Body Myositis: Long-term Extension of RESILIENT. Neurology. PubMed 33597289
- Rooks D, Swan T, Goswami B, et al. (2020). Bimagrumab vs Optimized Standard of Care for Treatment of Sarcopenia in Community-Dwelling Older Adults: A Randomized Clinical Trial. JAMA Netw Open. PubMed 33074327
Ostarine
- Dias JP, Dobs AS. (2026). Will Selective Androgen Receptor Modulators Ever Reach The Clinic? J Clin Endocrinol Metab. PubMed 41670367
- Dalton JT, Barnette KG, Bohl CE, Hancock ML, et al. (2011). The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II trial. J Cachexia Sarcopenia Muscle. PubMed 22031847
- Dobs AS, Boccia RV, Croot CC, Gabrail NY, et al. (2013). Effects of enobosarm on muscle wasting and physical function in patients with cancer: a double-blind, randomised controlled phase 2 trial. Lancet Oncol. PubMed 23499390
- Crawford J, Prado CM, Johnston MA, Gralla RJ, et al. (2016). Study Design and Rationale for the Phase 3 Clinical Development Program of Enobosarm, a Selective Androgen Receptor Modulator, for the Prevention and Treatment of Muscle Wasting in Cancer Patients (POWER Trials). Curr Oncol Rep. PubMed 27138015
The full evidence reviews
- Bimagrumab: the fat-loss antibody that failed its pivotal trial
An anti-ActRII monoclonal antibody — not a peptide, not for sale — that reliably strips fat and adds lean mass, has never improved physical function in a randomized trial, and is now in phase 2 alongside GLP-1 drugs.
Updated August 2026
- Ostarine (enobosarm): the clinical drug behind the black-market compound
Ostarine is enobosarm — a real SARM with two completed phase 3 trials. They found the same thing twice: lean body mass went up, physical function did not. That dissociation, not the bodybuilding folklore, is what you need to know.
Updated August 2026
Go deeper
GLP-1 medications and muscle: what the body-composition data actually show
Some of the weight lost is lean mass — but the substudies show fat falls faster, the ratio improves, and resistance training plus protein is what protects muscle.