Follistatin 344
Follistatin-344 is a research-grade form of the full-length follistatin isoform, a TGF-beta superfamily-binding glycoprotein studied preclinically for skeletal-muscle growth via myostatin/activin pathway modulation; research protocols typically use 50 mcg intramuscularly pre-workout.
It has been studied primarily in preclinical models for skeletal-muscle growth and hypertrophy via myostatin/activin pathway modulation, with additional research interest in muscle-wasting and fibrosis contexts.
Follistatin-344 (FS-344) is a research-grade form of follistatin, a secreted glycoprotein in the TGF-beta superfamily-binding protein family. The "344" designation refers to the full-length circulating isoform, distinguished by a C-terminal extension from the shorter, more tissue-local isoforms (FS-288, FS-315); structurally it comprises a heparin-binding N-terminal domain plus three cysteine-rich follistatin domains. Mechanistically, it acts not as a receptor agonist but as a high-affinity ligand trap: research has characterized it binding and sequestering myostatin (GDF-8), activin A, and related TGF-beta family ligands, with structural studies showing two follistatin molecules encircling the ligand to bury its type I and type II receptor binding sites.
This prevents engagement of the ActRIIA/ActRIIB receptors and the downstream SMAD2/3 signaling that normally restrains muscle growth. Most characterization comes from preclinical and gene-therapy research; FS-344 is not an FDA-approved drug and is used as a research compound.
Research literature on injectable follistatin peptide protocols is limited and not standardized; most rigorous data derive from gene-therapy and animal models rather than validated human dosing regimens.
No validated human time-to-effect has been established; animal and gene-therapy research has reported muscle-mass changes over a course of weeks rather than acutely.
In research and anecdotal contexts it is sometimes discussed alongside growth-hormone secretagogues or other myostatin-pathway compounds, though controlled human stacking data are lacking.
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This page is educational reference material about compounds studied in research settings. It is not medical advice, and nothing here is a recommendation to buy, possess, or use any compound. Research findings described are from published literature; individual compounds may not be approved for human use. Talk to a licensed clinician about anything that affects your health.