Performance & GH axis
Bimagrumab
BYM338
Bimagrumab is a human monoclonal antibody against the activin type II receptor, investigated for increasing muscle mass and, more recently, for preserving lean mass during GLP-1-induced weight loss. It is an antibody, not a peptide, and is not approved for any indication.
Also known as: BYM 338
- Status
- Bimagrumab is in Phase 2 clinical trials and not approved.
- Evidence
- Early human data. Only small or early-phase studies in people so far.
- Half-life
- Roughly 2 to 3 weeks, typical of a monoclonal antibody.
- How it's taken
- Intravenous or subcutaneous infusion (investigational)
- Mechanism
- Anabolic (IGF-1 / myostatin)
- Pathways
- Myostatin
How Bimagrumab works
Bimagrumab blocks the activin type II receptors ActRIIA and ActRIIB, which are the receptors through which myostatin, activin A and related ligands signal to restrain skeletal muscle growth. Blocking the receptor removes that restraint, increasing muscle mass. Trials have also consistently shown a reduction in fat mass, a less well-explained effect that has driven renewed interest.
What research has looked at
- Phase 2 studies reported increased lean body mass and decreased fat mass in adults with obesity and type 2 diabetes.
- It is being investigated in combination with GLP-1 receptor agonists specifically to address the loss of lean mass that accompanies rapid incretin-driven weight loss — a genuine clinical concern with that class.
- Because it acts at the receptor rather than on a single ligand, it blocks myostatin and activin signalling together.
Evidence level: Early human data. Only small or early-phase studies in people so far. These are areas studied or reported, not promised effects.
Reported side effects and risks
- It failed its primary endpoint in a Phase 2/3 trial in sporadic inclusion body myositis, despite increasing muscle mass. Muscle mass gain did not translate into functional benefit in that condition, which is an important caution against equating the two.
- Muscle spasms, acne and diarrhea were among the more frequent adverse events in trials.
- Elevations in liver enzymes and in pancreatic enzymes have been reported.
- It is not approved by any regulator for any indication.
- Long-term consequences of chronic activin receptor blockade in healthy people are unknown; the activin pathway has roles well beyond skeletal muscle, including in reproduction and in tumour suppression.
Sources
- PubMed research on bimagrumab activin receptor lean mass · NIH · National Library of Medicine
- DrugBank record for bimagrumab · DrugBank
- Active clinical trials for bimagrumab · U.S. National Library of Medicine
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Bimagrumab FAQ
What is Bimagrumab?
Bimagrumab is a human monoclonal antibody against the activin type II receptor, investigated for increasing muscle mass and, more recently, for preserving lean mass during GLP-1-induced weight loss. It is an antibody, not a peptide, and is not approved for any indication.
How does Bimagrumab work?
Bimagrumab blocks the activin type II receptors ActRIIA and ActRIIB, which are the receptors through which myostatin, activin A and related ligands signal to restrain skeletal muscle growth. Blocking the receptor removes that restraint, increasing muscle mass. Trials have also consistently shown a reduction in fat mass, a less well-explained effect that has driven renewed interest.
Is Bimagrumab FDA approved?
No. Bimagrumab is in Phase 2 clinical trials and not approved. Evidence level: early human data. Only small or early-phase studies in people so far.
What is the half-life of Bimagrumab?
Reported half-life: Roughly 2 to 3 weeks, typical of a monoclonal antibody.
How is Bimagrumab taken?
Intravenous or subcutaneous infusion (investigational).
What side effects have been reported with Bimagrumab?
Reported in the sources: It failed its primary endpoint in a Phase 2/3 trial in sporadic inclusion body myositis, despite increasing muscle mass. Muscle mass gain did not translate into functional benefit in that condition, which is an important caution against equating the two; Muscle spasms, acne and diarrhea were among the more frequent adverse events in trials; Elevations in liver enzymes and in pancreatic enzymes have been reported; It is not approved by any regulator for any indication; Long-term consequences of chronic activin receptor blockade in healthy people are unknown; the activin pathway has roles well beyond skeletal muscle, including in reproduction and in tumour suppression.
Educational summary compiled from the sources listed above. Not medical advice. Peptide Vault does not sell, source or recommend any compound. Talk to a qualified clinician before starting or changing anything.