Also known as: BYM338
Body composition improvement (fat loss with muscle preservation)
Amount
10 mg/kg
Frequency
Every 4 weeks (Q4W)
Duration
48 weeks
Route
IVTiming
Administered as IV infusion at clinical sites. The BELIEVE trial used approximately Q12W dosing (4 infusions over 48 weeks) in combination with semaglutide.
Duration
48 weeks
Repeatable
Yes
DEXA body composition scan
When: Baseline
Why: Baseline fat mass and lean mass measurement
HbA1c
When: Baseline
Why: Baseline glycemic control assessment
CMP (Comprehensive Metabolic Panel)
When: Baseline
Why: Baseline liver and kidney function
DEXA body composition scan
When: 24 weeks
Why: Monitor fat mass and lean mass changes
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Bimagrumab (BYM338) is a fully human IgG1 monoclonal antibody that binds to and blocks activin type II receptors (ActRIIA and ActRIIB). By blocking these receptors, bimagrumab prevents signaling by myostatin, activin A, and other TGF-beta superfamily ligands that normally limit muscle growth and promote fat accumulation. The result is simultaneous muscle preservation (or growth) and fat loss, a combination not achieved by most weight loss therapies.
Originally discovered by Novartis, bimagrumab was tested in muscle wasting conditions including inclusion body myositis (IBM), sarcopenia, and COPD. After disappointing results in IBM (the RESILIENT trial failed its primary endpoint), Novartis licensed the molecule to Versanis Bio, which repositioned it for obesity and cardiometabolic disease. Eli Lilly subsequently acquired Versanis Bio in 2023 for up to $1.925 billion, primarily for the bimagrumab asset.
Bimagrumab binds competitively to both ActRIIA and ActRIIB at the ligand binding site, with greater than 200-fold binding preference for ActRIIB over ActRIIA (though both affinities are subnanomolar). This blocks signaling by multiple TGF-beta superfamily ligands:
By blocking these ligands at the receptor level, bimagrumab prevents downstream Smad2/3 phosphorylation, sparing myosin heavy chain from degradation and promoting muscle protein synthesis.
Bimagrumab produces two simultaneous effects:
This dual action is particularly valuable in the context of GLP-1 receptor agonist therapy, where 20-40% of weight loss typically comes from lean mass rather than fat.
Effect of bimagrumab vs placebo on body fat mass among adults with type 2 diabetes and obesity: a phase 2 randomized clinical trial, published in JAMA Network Open (Heymsfield SB et al., 2021; PMID: 33439265):
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See real-world usage patterns alongside the clinical evidence above. Community-sourced, not clinically verified.
Based on 40+ community reports
View community protocolsEnobosarm (Ostarine/GTx-024): oral SARM for muscle preservation during GLP-1 weight loss. QUALITY Phase 2b positive. PLATEAU trial with tirzepatide planned.
Follistatin: Activin-binding myostatin inhibitor for muscle growth. Covers FST isoforms, gene therapy dystrophy trials, dosing, and safety data.
GDF-8 (Myostatin): Muscle growth negative regulator guide. Covers TGF-beta signaling, double-muscling mutations, inhibitor therapies, and research.
ACE-031: ActRIIB-Fc myostatin inhibitor for muscle wasting. Covers mechanism, Duchenne dystrophy trials, dosing, side effects, and clinical status.
This website is for educational and informational purposes only. The information provided is not intended to diagnose, treat, cure, or prevent any disease. Always consult with a qualified healthcare professional before using any peptide or supplement.
Research review of peptides targeting sarcopenia and age-related muscle loss, including myostatin inhibitors, growth factors, and GH secretagogues with clinical trial data.
A research review of lean mass loss during GLP-1 treatment, with DEXA data from STEP and SURMOUNT trials, and emerging strategies including bimagrumab, resistance training, and high-protein diets.
A research review comparing bimagrumab, trevogrumab, and apitegromab โ three anti-myostatin antibodies in clinical development for muscle preservation, obesity, and spinal muscular atrophy.
A research review of non-GLP-1 peptide approaches to weight loss โ amylin analogs (cagrilintide, petrelintide, pramlintide), melanocortin agonists (setmelanotide, bivamelagon), and anti-myostatin antibodies (bimagrumab).
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