For research and educational purposes only. Not medical advice.

Follistatin Reference

Educational, not medical advice reference for Follistatin: Growth Factor; regulatory status, evidence posture, source review, and schedule notes…

Plain English

What it is
Follistatin is a protein the body makes naturally that blocks myostatin and activin, the signals that limit muscle growth. It is not approved by the FDA as a medicine for any use. The only real human studies used a gene-therapy version (AAV1-FS344) run at a single hospital, and the 'Follistatin 344' or '315' vials sold as research chemicals are a different product with no human trial program.
What people use it for
In the muscle-building research community, people bring it up because lab studies showed it is one of the strongest natural myostatin blockers, and raising it in mice produced large gains in muscle. There is no approved human use for building muscle.
What the science shows
The foundation is animal and lab work in mice. The human record is two small, early-stage, non-randomized gene-therapy trials in muscle-wasting diseases (Becker muscular dystrophy and inclusion body myositis), which tracked walking tests in a handful of patients. No large, high-quality randomized human trial of any follistatin product exists, and the research-vial peptide has no human results at all.
The catch
Research-vial follistatin is not the same molecule as the gene-therapy version that was studied, and it carries a research-chemical posture with no proof it works or is safe in people. Myostatin-pathway agents like follistatin are banned in sport at all times by the World Anti-Doping Agency.

Reference summary

Foundational biology is Lee & McPherron 2001 PNAS, which established follistatin as a potent endogenous myostatin/activin inhibitor and showed that follistatin overexpression in mice produces substantial muscle hypertrophy. Human experience is the two small AAV1-FS344 gene-therapy trials (Becker MD, IBM) - non-randomized open-label, small samples, surrogate endpoints. There is no large randomized human trial of any follistatin product.

Regulatory and posture

Categories
Growth Factor
Aliases
FST, FST-344, FST-315, AAV1-FS344 (gene therapy construct), Activin-binding protein
Evidence posture
preclinical - Animal models and a small gene-therapy program only. No randomized controlled trial of any research-vial follistatin peptide product exists.
Regulatory status
Not FDA-approved as a drug for any indication. Follistatin is an endogenous activin-binding glycoprotein. The clinical experience to date is the AAV1-FS344 gene-therapy program led at Nationwide Children's Hospital (Mendell 2015 Mol Ther, Becker MD; Mendell 2017 Mol Ther, sporadic inclusion body myositis), which ran Phase 1/2a only and did not advance to a Phase 3 program. Recombinant or research-vial 'Follistatin 344 / 315' peptide products sold in the research-chemical market are not the same molecule as the gene-therapy construct and are not FDA-approved. WADA-prohibited at all times as a myostatin-pathway agent (S4).
Content review status
research reference

Selected public sources

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