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Metabolic & Weight Management

Bimagrumab

Also known as BYM338 · Versanis drug

Emerging researchIntravenous infusionSubcutaneous injection (co-formulation in development)Investigational; not approved by the FDA for any indication. It is a biologic monoclonal antibody in clinical development (Eli Lilly), not a small-molecule peptide, and is not a compounded 503A/503B product or available through standard pharmacy compounding. As an unapproved investigational agent it is restricted to clinical trials. Athletes should note that agents acting on the myostatin/activin pathway are prohibited at all times under the WADA Prohibited List in class S4 (Hormone and Metabolic Modulators), subsection S4.3, 'Agents Preventing Activin Receptor IIB Activation' — the category in which bimagrumab is named by example — and are classified as non-Specified Substances.

Bimagrumab is a fully human monoclonal antibody (not a peptide) that binds and blocks activin type II receptors (ActRIIA/ActRIIB), preventing signaling by myostatin and activin, which normally limit muscle growth. In research this receptor blockade has been associated with increases in lean muscle mass alongside reductions in fat mass and visceral adiposity. Originally developed by Novartis (with MorphoSys) for sporadic inclusion body myositis, where a Phase 2b/3 study failed in 2016, it was later repositioned for obesity and metabolic indications by Versanis Bio and acquired by Eli Lilly in 2023. Human Phase 2 trials, including the BELIEVE study evaluating it alone and combined with semaglutide, have reported fat-mass reduction with relative lean-mass preservation. It remains investigational; in 2025 Lilly terminated a tirzepatide-bimagrumab Phase 2b trial in type 2 diabetes while an obesity-focused combination study continued.

Studied / used for

  • Investigated for fat-mass reduction in obesity and overweight
  • Studied for preserving or increasing lean muscle mass during weight loss
  • Investigated in combination with GLP-1 agonists (e.g., semaglutide) for obesity
  • Studied for body-composition and glycemic measures in type 2 diabetes
  • Originally studied for sporadic inclusion body myositis and sarcopenia

Commonly reported side effects

  • Muscle spasms or cramps (commonly reported)
  • Diarrhea, more often reported after initial dosing (commonly reported)
  • Acne or transient skin eruptions (commonly reported)
  • Mild, transient injection/infusion-related events (commonly reported)
Emerging research. Active research; human evidence still developing. This reflects the strength of the research base, not effectiveness or a recommendation.

Not medical advice.

This is an educational reference. Peptalk does not recommend, prescribe, endorse, or rate any compound, and provides no dosing information. Do not start, stop, or change any peptide, hormone, supplement, or therapy based on this page. All clinical decisions must be made with your licensed healthcare provider.

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