Follistatin
Also known as: Follistatin-344, FS-344, FST
A naturally occurring protein that inhibits myostatin and activin A, two signals that limit muscle growth. While often associated with bodybuilding, it also has applications in hair growth and is being studied in gene therapy for muscular dystrophy. Myostatin inhibitors are in Phase 3 trials from multiple pharmaceutical companies.
How it works
Follistatin is your body's natural brake on myostatin, a protein that tells muscles to stop growing. By binding to both myostatin and activin A, follistatin removes the growth limit and allows muscles to develop more freely. Follistatin-344 is the variant most studied because it works throughout the body (systemic delivery), while other forms tend to stay local. It is also being explored in gene therapy, where a DNA plasmid delivers the follistatin gene directly to cells for effects that can last about a year.
Common uses
- Muscle growth and preservation (research)
- Hair growth and follicle health (research)
- Muscular dystrophy treatment (gene therapy trials)
- Body composition improvement (experimental)
Side effects
- Slight increase in LDL cholesterol (reported in about one-third of gene therapy patients)
- Injection site reactions
- Limited data on long-term safety of injectable peptide form
- Theoretical reproductive effects (activin A plays a role in reproduction)
- Unknown long-term effects of myostatin suppression
Key research
- First human gene therapy trial for follistatin completed in muscular dystrophy patients showed improved ambulation
- Scholar Rock's myostatin inhibitor (apitegromab) is seeking FDA approval based on Phase 3 SMA trials
- Over 500 patients treated with follistatin gene therapy with good tolerability
- Multiple Phase 3 trials underway from Scholar Rock, Biohaven, and Roche for myostatin inhibition in SMA
Safety notes
- Injectable follistatin peptide is not FDA-approved and is sold for research use only
- Gene therapy approach is being developed through proper clinical channels
- The peptide form has a very short half-life, requiring frequent injections
- Myostatin inhibition could have unknown long-term effects on heart muscle and other tissues
- Quality of research-grade products varies widely
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