Activin type II receptor antibody

Bimagrumab

Published phase 2 evidence now includes bimagrumab combined with semaglutide.

Evidence Maturity · M3 - Clinical Investigational for obesity
Evidence reviewed: September 19, 2026Source-labeled

Signal summary

Bimagrumab has controlled body-composition evidence from an older diabetes trial and the larger 2026 BELIEVE combination trial below.

Signal interpretation: Bimagrumab shows why body-composition intelligence can reveal something the scale misses: modest weight loss can coexist with very large fat loss if lean tissue rises.

Study details

Doses studied — not a dosing recommendation. Regimens belong to the named study, formulation and population.

BELIEVE randomized phase 2 trial

Population
507 adults with obesity/overweight and complications, excluding diabetes; nine groups.
Doses and administration studied
Bimagrumab 10 or 30 mg/kg intravenously every 12 weeks; semaglutide 1.0 or 2.4 mg subcutaneously weekly; monotherapy and combination arms.
Duration
48-week main period; open-label extension to week 72
Reported finding / status
At week 48, the high-dose combination produced -17.8 kg weight change versus -14.2 kg with semaglutide 2.4 mg (treatment-regimen estimand). Combinations reduced lean-mass loss relative to semaglutide alone.
Interpretation and limitations
Only 74.4% completed the main period. Muscle spasms, diarrhea and acne occurred. Functional measures were mixed/exploratory; preservation is not proven long-term functional benefit.

Source tier B · Read the original study or record

Outcome Evidence Strength

Weight change3/5
Fat-mass change4/5
Lean-mass change4/5
Strength / function benefit2/5

Weight: published phase 2 RCT. Fat and lean: controlled findings in BELIEVE and the older diabetes trial. Function: exploratory, mixed findings; not confirmatory.

Editorial evidence ratings for the cited outcomes, not effect size or treatment recommendations. A lean-mass score may describe loss. 0 means not established in the reviewed evidence, not proof of no effect. Read the rubric.

Earlier evidence: 2021 diabetes trial

  • In a 48-week randomized Phase 2 trial, fat mass decreased 20.5% with bimagrumab versus 0.5% with placebo.
  • Lean mass increased 3.6% with bimagrumab versus a 0.8% decrease with placebo.
  • Body weight decreased 6.5%, meaning its composition effect was much larger than the scale alone would suggest.

What is not established?

  • The study included 75 adults with type 2 diabetes and overweight/obesity; it is not a broad Phase 3 obesity dataset.
  • An increase in lean mass does not automatically establish improved strength or physical function.
  • BELIEVE provides published combination evidence; confirmatory and longer-term outcomes remain important.

Evidence sources

A = regulatory/official • B = peer-reviewed randomized/meta-analysis • C = peer-reviewed review/observational • D = registered trial • E = sponsor-reported • F = preclinical

Source tier B: Peer-reviewed randomized Phase 2 trial
Effect of Bimagrumab vs Placebo on Body Fat Mass
Educational use only. This page summarizes research evidence and regulatory status. Study doses describe research, not prescribing instructions. This page does not provide personalized dosing, self-use protocols, sourcing, or a recommendation to use this therapy.