Also known as fst344, fs344 · Wikipedia
Follistatin-344 (FST-344, FS-344) is a 344-amino-acid splice isoform of the endogenous activin-binding glycoprotein follistatin. It is marketed as a research peptide for myostatin inhibition and skeletal-muscle hypertrophy, with most credible human evidence coming from AAV-delivered gene-therapy programs (Acceleron / Nationwide Children's Hospital under Jerry Mendell) for Becker muscular dystrophy and sporadic inclusion-body myositis rather than from injected recombinant protein. Because FST-344 is a large, glycosylated protein with a serum half-life measured in minutes and rapid heparin/extracellular-matrix sequestration, subcutaneous vendor product is mechanistically unlikely to achieve meaningful systemic bioactivity. Also known as: FST344; FS344.
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Browse all vendorsMechanism of action
Follistatin-344 is a 344-aa splice isoform of endogenous follistatin that functions as a high-affinity decoy ligand for TGF-beta superfamily members myostatin (GDF-8) and activins A/B, preventing receptor engagement at ActRIIB and downstream Smad2/3 signaling. By relieving the myostatin brake on satellite-cell activation and protein synthesis, follistatin produces skeletal-muscle hypertrophy in preclinical models (https://pubmed.
Pharmacokinetic properties
Half-life
Native follistatin protein has a very short serum half-life (~minutes); the heparin-binding 344 isoform binds tissue extracellular matrix rapidly. Gene-therapy (AAV-FST) delivers durable expression
Routes
intramuscular (gene therapy) · subcutaneous (vendor protein — questionable)
Bioavailability
Vendor-sold lyophilized recombinant or synthesized follistatin is unlikely to remain bioactive after subcutaneous injection: as a 344-aa glycoprotein it requires correct folding and glycosylation, and the molecule is rapidly cleared. Meaningful systemic effects from SC self-administration are mechanistically implausible. Gene-therapy approaches (AAV1-FS344) bypass this by driving in-situ muscle expression.
Amino-acid sequence
(Glycoprotein, 344 aa; sequence too long for label field)
Use & research dosing
There is no validated human dose for injected recombinant follistatin-344. Self-experimentation protocols commonly report 100 mcg subcutaneously daily or every other day for 10-30 day cycles, despite serious bioactivity concerns for a 344-aa glycoprotein delivered SC. The only systematic human data come from AAV gene-therapy trials (Mendell et al., BMD and sIBM): AAV1.CMV.FS344 was delivered by direct bilateral intramuscular quadriceps injection at 3 x 10^11 vg/kg/leg (Cohort 1) and higher in subsequent cohorts (https://pmc.ncbi.nlm.nih.gov/articles/PMC4426808/) - not transferable to recombinant-protein dosing.
Research-use framing only. SavePeptides sells nothing for human consumption. Doses above reflect reported research / self-experimentation ranges, not clinical recommendations.
Major factual landmine: vendor-sold subcutaneous follistatin-344 is unlikely to be systemically bioactive. It is a 344-aa glycoprotein requiring correct folding and glycosylation, has a serum half-life of minutes, and is rapidly sequestered to extracellular matrix. The only credible clinical progress has been AAV gene therapy (Mendell group) for Becker muscular dystrophy and sporadic inclusion-body myositis, with mixed independent replication (https://pmc.ncbi.nlm.nih.gov/articles/PMC5628928/). Research subjects considering this peptide should treat marketing claims of muscle hypertrophy from SC self-administration with extreme skepticism.
— SavePeptides editorial desk · last updated 2026-05-25
Cautions & contraindications
Research foundation
Facts verified
2026-05-25
Confidence
low
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