Head-to-head

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.

Bimagrumab

BYM338, LY3985863

Clinical data

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 review

Ostarine

Enobosarm, MK-2866, GTx-024

Clinical data

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 review

Side by side

	Bimagrumab	Ostarine
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
Evidence grade	Clinical data	Clinical data
Family	Hormonal	Hormonal
Key human source	RESILIENT phase 2/3, Lancet Neurol 2019	POWER phase 3 program, Lancet Oncol 2013

marks a row where the two differ. Evidence grades come from our evidence matrix, which grades each molecule on the human data for the use it is marketed for.

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.

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.