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Growth Factors & IGF

Follistatin-344

Also known as FS-344 · FST-344 · Follistatin

Emerging researchIntramuscular (used in the AAV gene-therapy trial)Subcutaneous (reported for research-grade peptide material)Not approved by the FDA for any indication; follistatin gene therapy has only been studied under investigational (IND) status in clinical trials. Because no follistatin drug is FDA-approved, there is no legitimate 503A or 503B compounding pathway for it, and material sold by research-chemical vendors is labeled "for research use only," not for human use, and is not FDA-regulated for purity or safety. Follistatin is prohibited in sport by WADA as a myostatin inhibitor (Section S4, Hormone and Metabolic Modulators), and AAV/gene-vector forms additionally fall under the prohibited Gene and Cell Doping methods (M3).

Follistatin-344 (FS-344, or FST-344) refers to the full-length 344-residue follistatin precursor encoded by the follistatin gene — the construct delivered in muscular-dystrophy gene-therapy trials — rather than one of the mature secreted isoforms (FS-288, FS-300, FS-315). Follistatin is a glycoprotein the body produces that binds and neutralizes members of the TGF-beta family, most notably myostatin and activin. By sequestering these ligands, follistatin reduces SMAD2/3 signaling through the activin type II receptor, a pathway that normally restrains skeletal-muscle growth; researchers have therefore studied it as a myostatin antagonist. The only human data come from a small open-label Phase 1/2a gene-therapy trial that delivered the FS344 gene via an adeno-associated virus (AAV1-FS344) by intramuscular injection in Becker muscular dystrophy and sporadic inclusion body myositis, which reported measures of muscle volume and walking distance over roughly two years without serious adverse events. That human evidence is for the AAV gene-therapy construct, not for the injectable research-grade peptide. Most remaining evidence is preclinical, where follistatin overexpression markedly increased muscle mass in animal models. Follistatin-344 is not an FDA-approved drug, and the synthetic peptide sold to research vendors has not been characterized for safety or pharmacokinetics in humans.

Studied / used for

  • Investigated for influencing skeletal-muscle mass via myostatin and activin binding
  • Studied in a small gene-therapy trial for Becker muscular dystrophy
  • Studied in sporadic inclusion body myositis as a muscle-wasting condition
  • Investigated in preclinical models for muscle hypertrophy and fibrosis changes
  • Investigated for its role in TGF-beta / activin signaling regulation

Commonly reported side effects

  • Injection-site reactions such as redness, swelling, or pain commonly reported
  • Local inflammation at the administration site commonly reported
  • Reports of hormonal or reproductive-axis effects given follistatin's activin-binding role
  • Concerns about unverified purity and contamination are commonly reported with research-grade material
Emerging research. Active research; human evidence still developing. This reflects the strength of the research base, not effectiveness or a recommendation.

Not medical advice.

This is an educational reference. Peptalk does not recommend, prescribe, endorse, or rate any compound, and provides no dosing information. Do not start, stop, or change any peptide, hormone, supplement, or therapy based on this page. All clinical decisions must be made with your licensed healthcare provider.

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