Follistatin 344

Also known as FST-344, FS-344, Follistatin-344, FST344

A recombinant follistatin isoform that binds and neutralizes myostatin and activins to promote muscle growth; the most credible human evidence comes from AAV gene therapy, not injected peptide.

Molecular weight~37–49 kDa recombinant glycoprotein (344-aa precursor; varies with glycosylation)

Half-life~12–36 hours (estimated; the C-terminal heparin-binding tail of the 344 isoform prolongs tissue retention).

CategoryGrowth & GH

Typical use cases

✓ Myostatin inhibition research✓ Muscle growth/strength studies✓ Muscular dystrophy models✓ Fibrosis/tissue research

Dosing guidelines

StartingResearch context: ~100 mcg/day SC for short cycles (e.g. 10–30 days) is commonly cited; no validated human dose.

Maintenance~100 mcg/day during a cycle; not standardized.

Max (studied)Undefined; informal protocols rarely exceed ~300 mcg/day — treat as an unverified research ceiling.

Titration

Typically flat-dosed within a short cycle; no validated titration scheme.

Reconstitution

1 mg vial: add ~1–2 mL bacteriostatic water (~0.5–1 mg/mL = 50–100 mcg per 0.1 mL); swirl gently.

Injection sites

Subcutaneous (abdomen/thigh), rotate sites.

Storage & handling

Lyophilized: stable months cool/dark, longer frozen. Reconstituted: refrigerate (2–8 °C).

Side effects

Injection-site reaction Mild · Uncommon
Possible effects on reproductive/pituitary (FSH) axis (theoretical) Moderate · Rare
Headache / fatigue Mild · Uncommon
Unknown long-term effects (limited human data) Moderate · Uncommon

Research summary

Follistatin is an endogenous glycoprotein that wraps around and neutralizes TGF-β family ligands — chiefly myostatin (GDF8) and activins — de-repressing skeletal-muscle growth. FS-344 is the full-length 344-amino-acid precursor, processed to the circulating FS-315 and tissue-bound FS-288 isoforms. The strongest human data come from an AAV1-FS344 gene-therapy trial (Mendell et al.) in Becker muscular dystrophy and inclusion body myositis showing functional gains over ~2 years — there are no robust human trials of injected follistatin peptide itself, so the research-peptide use is largely extrapolated from gene-therapy and animal work. Educational only — not medical advice.

Key references

Lee & McPherron, PNAS (2001) — follistatin and myostatin regulation of muscle mass
Mendell et al., Molecular Therapy (2015) — AAV1-FS344 gene therapy in BMD/IBM patients

Related compounds

ACE-031 → Myostatin (GDF8) YK-11

Where to buy

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Educational reference only — not medical advice. Dosing figures are commonly-cited ranges, not prescriptions. Consult a qualified clinician.

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