Follistatin-344

Follistatin is an endogenous glycoprotein that binds and neutralises members of the TGF-β superfamily, most notably myostatin (GDF-8) and activins. Myostatin is a negative regulator of skeletal muscle mass; by sequestering it, follistatin releases a brake on muscle growth, allowing satellite-cell activation and fibre hypertrophy. FS344 is a specific follistatin isoform of 344 amino acids that is secreted and post-translationally processed to the circulating FS315 form, which has comparatively lower affinity for activin than the cell-surface-bound FS288 isoform — a property intended to bias its action toward muscle while limiting broader activin-related effects. The best-characterised delivery is not an injected peptide but an adeno-associated virus (AAV) vector carrying the FS344 gene, driving local, durable follistatin expression in muscle.

Evidence for FS344 is preclinical and early-phase gene-therapy data, not injectable-peptide data. Kota et al. (Sci Transl Med, 2009) showed that a single intramuscular injection of an AAV1 vector expressing a follistatin isoform produced pronounced, durable increases in muscle size and strength in cynomolgus macaques without organ pathology. Mendell et al. (Mol Ther, 2015) conducted a phase 1/2a AAV1-huFollistatin344 gene-therapy trial in Becker muscular dystrophy, reporting improved ambulation in some patients — described as the first gene-therapy trial to show functional improvement in a muscular dystrophy. Crucially, these results derive from AAV-delivered gene expression under clinical oversight, not from self-administered 'follistatin' peptide, for which controlled human efficacy data are absent.

Educational overview only — no dosing instructions in the public hub. The validated data are from AAV-delivered FS344 in controlled trials, not from self-administered peptide.

Unchecked myostatin/activin inhibition raises theoretical and preclinical concerns: disorganised or excessive tissue growth, effects on tendon integrity and cardiac muscle, and off-target actions across other TGF-β pathways (activins regulate reproduction, inflammation, and fibrosis). Long-term human safety of injectable 'follistatin' material is unknown, and AAV gene therapy carries its own risks (immune responses to vector and transgene, irreversibility of expression). Sourcing and purity are major practical risks for any gray-market product, and the identity of a large glycoprotein is hard to confirm. As a myostatin/activin-pathway modulator, follistatin is prohibited in sport at all times.

No approved injectable follistatin product exists for human use. Follistatin is a large, glycosylated protein whose correct folding and glycosylation are difficult to reproduce and verify; a short peptide sold as 'follistatin' cannot reproduce the biology of the full protein. Any research material should carry a recent third-party Certificate of Analysis (identity, purity, quantification, mass spectrometry) as a minimum, recognising that end-user verification of a glycoprotein is inherently limited. Content here reflects the gene-therapy construct and protein as studied, not gray-market material of unverified composition.

Not approved for human use in any major jurisdiction; sold research-use-only (RUO), and supplying it for human consumption is unlawful in most jurisdictions. Gene-therapy forms (AAV1-huFollistatin344) remain investigational and confined to registered clinical trials. As a myostatin/activin-pathway modulator it is on the WADA Prohibited List (class S4, hormone and metabolic modulators) and is banned in sport at all times.