Bimagrumab
Metabolic Health · Activin receptor antagonist
Tier C+
What this is
Heymsfield JAMA 2021: -20.5% fat mass with +3.6% lean mass gain at 48 weeks. Unique profile: most weight-loss drugs (incl. GLP-1s) cost ~25-30% of weight loss as lean mass. Now owned by Lilly — actively being explored as combo with tirzepatide for body recomposition. Highlighted in 2026 obesity-pharmacotherapy reviews (Lempesis & Dalamaga, Metabol Open) as the prototype lean-mass-preservation agent. BELIEVE (Phase 2b): bimagrumab preserved or increased lean mass while semaglutide alone reduced it, and bimagrumab + semaglutide produced the greatest total weight loss. No Phase 3 readout yet.
Mechanism
Monoclonal antibody blocks activin type II receptors — reduces myostatin/activin signaling; increases muscle mass while reducing fat mass (body recomposition effect)
Dose & route
Phase 2 trials used 10 mg/kg IV every 4 weeks
Citations
- https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2776354
- https://pubmed.ncbi.nlm.nih.gov/33433648/
- https://doi.org/10.1016/j.metop.2026.100463
- https://doi.org/10.1002/jcsm.70298
- https://clinicaltrials.gov/study/NCT01601600
- https://pubmed.ncbi.nlm.nih.gov/39385353/
- https://pubmed.ncbi.nlm.nih.gov/41178728/
- https://clinicaltrials.gov/study/NCT01433263
- https://doi.org/10.3390/nu18091352
- https://doi.org/10.1186/s12933-026-03140-0
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This is an independent synthesis of published research by a non-clinician. Scores are opinions supported by citations, not prescriptions. See the full disclaimer and methodology for how this score was produced and what it does and doesn't mean.