Follistatin isoform (344 amino acids) / myostatin and activin antagonist
Follistatin-344 is a form of the natural protein follistatin that blocks myostatin and activin to allow greater muscle growth.
| Class / type | Follistatin isoform (344 amino acids) / myostatin and activin antagonist |
|---|---|
| Category | Growth Hormone & Muscle |
| Status (Jul 2026) | Research use only |
It is a binding protein that binds myostatin and activin A with high affinity in the extracellular space, preventing them from activating ActRIIB and thereby releasing the natural limit on muscle growth.
Studied mainly via AAV-mediated gene therapy in Becker muscular dystrophy and inclusion body myositis, and in preclinical animal models for muscle hypertrophy and anti-fibrotic effects.
Gene-therapy trials reported increased muscle volume and strength over two years without serious adverse events; preclinical models show dramatic muscle growth.
Human data are very limited, injectable protein protocols are unvalidated, and follistatin's roles in reproductive and other TGF-beta pathways raise off-target and long-term safety concerns.
Users cite the large muscle-growth potential seen in animal and gene-therapy research; anecdotal sentiment only, not a medical endorsement.
NOT FDA-approved. It remains investigational (gene-therapy and preclinical research only) with no approved human product, and myostatin-inhibiting agents are prohibited by WADA under class S4.5.