Follistatin 344 is a naturally occurring glycoprotein (344 amino acids) that binds and neutralizes activin and myostatin, two TGF-β superfamily members that inhibit muscle growth. By blocking myostatin, follistatin allows greater muscle hypertrophy. Gene therapy approaches using follistatin (AAV1-FS344) have been tested in human clinical trials for Becker muscular dystrophy and inclusion body myositis. The recombinant protein version sold by research vendors has extremely limited human data.
Category: Growth Factor. Evidence rating: D (animal/preclinical only).
Clinical status: Gene therapy (AAV1-FS344): Phase I/II trials completed for Becker muscular dystrophy (Mendell et al., Mol Ther 2015) and inclusion body myositis (Mendell et al., Mol Ther 2017). Recombinant protein:…
Binds activin A, activin B, and myostatin with high affinity, preventing them from signaling through ActRII/ActRIIB receptors and downstream SMAD2/3 phosphorylation. Myostatin is a negative regulator of skeletal muscle mass — its inhibition leads to muscle hypertrophy. Follistatin also modulates…
Research base: 0 registered clinical trials and 7 indexed publications reference Follistatin 344.
Safety considerations: Gene therapy trials: generally well-tolerated with mild injection site reactions; one patient developed transient liver enzyme elevation; Recombinant protein: no human safety data; Theoretical concerns about reproductive effects (follistatin regulates FSH).
Reviewed by the PeptideAtlas Editorial Team. Last reviewed: 2026-07-06.
Related peptides: IGF-1 LR3, MGF, IGF-1 DES.
Compare: Follistatin 344 vs IGF-1 LR3, Follistatin 344 vs MGF, Follistatin 344 vs IGF-1 DES.
FST344 is the full-length isoform that circulates systemically. FST315 lacks the heparin-binding domain and has more localized action. FST288 binds to cell surfaces. The 344 form is most commonly discussed for muscle-building.
The recombinant protein has a half-life of only 2-4 hours, meaning brief injections may not sustain myostatin inhibition long enough. Gene therapy provides continuous expression. No human data supports injected recombinant follistatin for muscle building.
Follistatin 344 is a naturally occurring glycoprotein that binds and inhibits myostatin and activin, potentially promoting muscle growth and reducing muscle wasting.
FOLLISTATIN 344 has been studied for: Myostatin inhibition, Muscle growth support, Lean mass preservation, Recovery support. Full-length follistatin isoform; potent myostatin blocker.
Binds activin and myostatin with high affinity, neutralizing their growth-inhibitory signaling on skeletal muscle tissue.