Follistatin 344
FitnessAlso known as: FST-344, Follistatin isoform 344
Limited EvidenceWhat is Follistatin 344?
A 344-amino acid isoform of follistatin, a naturally occurring glycoprotein that binds and neutralizes myostatin — the protein that limits muscle mass. By inhibiting myostatin, follistatin theoretically removes the body's built-in ceiling on muscle growth. Popularized following myostatin knock-out animal studies, but human evidence for exogenous peptide administration is negligible.
How it works
Follistatin binds myostatin (GDF-8) with high affinity, sequestering it and preventing it from signaling through ActRIIB receptors. Myostatin is a negative regulator of muscle growth — without its inhibitory signal, satellite cells proliferate more freely and hypertrophy is less constrained. The FST-344 isoform has high affinity for heparan sulfate proteoglycans, anchoring it to local tissue rather than circulating systemically.
What marketers claim
- ▸removes the genetic ceiling on muscle mass
- ▸produces steroid-like gains without side effects
- ▸proven in humans based on animal studies
- ▸safe indefinitely at any dose
What evidence supports
- ✓gene therapy delivery to macaques produced significant muscle hypertrophy without toxicity (Nationwide Children's Hospital, 2009)
- ✓pilot gene therapy trial in Becker muscular dystrophy (6 patients) showed modest muscle function improvements
- ✓myostatin inhibition consistently produces hypertrophy across multiple animal species
Research evidence
Key studies on Follistatin 344, summarized in plain language. This is not an exhaustive list — it highlights the most relevant findings.
Follistatin gene delivery enhances muscle in nonhuman primates
Finding: 15–27% muscle mass increase in treated muscles with no adverse effects at 8-week follow-up; confirms follistatin-mediated myostatin inhibition is effective in primates.
Limitation: Gene therapy in primates is completely different from exogenous synthetic peptide injection; delivery mechanism, duration of expression, and systemic exposure differ fundamentally.
Pilot trial of follistatin gene therapy for Becker muscular dystrophy
Finding: Modest but measurable improvements in 6-minute walk test and muscle volume in treated limbs; no serious adverse events at 6-month follow-up.
Limitation: Disease population (BMD) with impaired baseline muscle function; gene therapy delivery mechanism; extremely small sample; results do not generalize to healthy adults seeking hypertrophy.
Best for
What to expect
Realistic timeline based on available research. Individual results vary.
Human timeline unknown
Gene therapy trials measured outcomes at 8 weeks post-administration. Peptide injection timeline, if any effect exists, is entirely uninvestigated in humans. The FST-344 isoform binds heparan sulfate proteoglycans, suggesting local tissue retention — but this has not been characterized pharmacokinetically for injected peptide.
Safety notes & concerns
Full safety guide →- ⚠virtually no human evidence for exogenous peptide administration — the gene therapy data involves completely different delivery
- ⚠follistatin also inhibits FSH — chronic suppression could impair reproductive function in both sexes
- ⚠follistatin inhibits activin, which has roles in bone density, glucose metabolism, and tumor suppression
- ⚠large protein peptides extremely difficult to synthesize correctly — commercial purity uncertain
- ⚠long-term systemic myostatin and activin blockade in healthy humans entirely unstudied
Pairs well with
Use caution with
Frequently asked questions
What about "super baby" and double-muscled cattle stories — don't they prove myostatin inhibition works?
These cases involve myostatin gene mutations (loss-of-function), not follistatin. The 2004 German infant case (born with extreme muscularity due to myostatin gene defect) and Belgian Blue cattle confirm myostatin's role in limiting muscle growth, but they do not validate exogenous follistatin peptide injections as a safe or effective way to replicate this effect in adults.
Why not take a follistatin supplement pill?
Follistatin is a ~35 kDa glycoprotein — it cannot survive oral digestion intact and would be broken down into individual amino acids before absorption. Many commercial "follistatin supplements" contain egg yolk powder (which naturally contains follistatin), but quantities present are far too small and not bioavailable in peptide form to affect systemic myostatin levels.
Related fitness peptides
those exploring growth hormone optimization under medical supervision
investigational GH axis optimisation in adults seeking to restore youthful GH pulsatility for recovery, sleep quality, and body composition — in a research context with physician oversight; Sermorelin is the more legally accessible clinical alternative in the US for similar goals
understanding GH secretagogue research — use under medical supervision only
research context — those exploring GH secretagogues under medical supervision
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Last updated: 2026-06-10
Medical Disclaimer
The information on this site is for educational and informational purposes only. It is not intended as medical advice and should not be used to diagnose, treat, or prevent any condition. Always consult with a qualified healthcare professional before starting any new supplement, peptide, or treatment protocol.