Follistatin-344
Also known as FST-344, Follistatin 344, FS344
Follistatin-344 is a naturally occurring glycoprotein that acts as a potent inhibitor of myostatin (GDF-8) — the primary biological brake on muscle growth. By binding and neutralizing myostatin, follistatin removes this ceiling, enabling significantly greater muscle hypertrophy. It also inhibits activin A and other TGF-β family members. Considered one of the most anabolic compounds in the research peptide space.
How it works
Follistatin binds myostatin (GDF-8) and activin A with high affinity, sequestering them from their receptors (ActRIIA/IIB). Myostatin normally signals via Smad2/3 to suppress satellite cell activation and myofiber growth. Blocking myostatin unleashes satellite cell proliferation and dramatically increases protein synthesis. FST-344 is the 344 amino acid isoform — the dominant circulating form.
Benefits
- Potently inhibits myostatin, removing the primary limit on muscle mass
- Promotes dramatic skeletal muscle hypertrophy
- Inhibits activin A, which may have anti-aging and muscle-preserving effects
- Potential for improved body composition (muscle gain + fat loss)
- May support fertility and ovarian function (activin inhibition)
- Animal models show 200%+ increases in muscle mass with gene therapy
Dosing
50–100 mcg · Once daily for 10 days
Typically run as a 10-day course (100mcg/day IM). Course-based — not continuous use. Significant anabolic effects expected within the course. Some users run 2 courses per year.
Ranges reflect commonly cited research protocols, not a prescription. Dose with a licensed provider.
Reconstitution
Reconstitute 1mg vial with 1mL BAC water = 1mg/mL. Extremely fragile — avoid vortexing, use gentle swirling only. Store at -20°C lyophilized.
Helix’s free reconstitution calculator gives you the exact draw volume → get the app
Common stacks
Reported side effects
- Injection site pain (can be significant)
- Potential hypertrophy of organs not just muscle (heart, gut — monitor)
- Possible effects on reproductive hormones (activin inhibition)
- Unknown long-term consequences of myostatin suppression
- Very limited human safety data
Who it’s for
Advanced bodybuilders or athletes seeking maximum hypertrophy who have exhausted conventional approaches. Requires extensive knowledge of peptide use. Not appropriate for beginners — long-term myostatin suppression has unknown consequences in humans.
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