WhatPeptide

Follistatin-344

A 344-amino-acid glycoprotein that functions as a potent endogenous inhibitor of myostatin (GDF-8) and activin A/B. Tested clinically as an AAV1-delivered gene therapy vector (AAV1.CMV.FS344) for muscular dystrophy, and available as a recombinant peptide through unregulated channels.

Moderate evidence Unregulated Myostatin Inhibitor

Written by WhatPeptide Editorial Team · Last updated 2026-03-18

Half-life

Protein: ~90 min (estimated); Gene therapy: sustained expression >15 months in primates (Kota et al., PMID 20368179)

Dosage range

Gene therapy: 3-6 × 10¹¹ vg/kg/leg IM (Mendell et al.); Peptide (unregulated): 100-200 mcg/day SC — not clinically validated

Administration

Subcutaneous injection

Research level

Moderate

How Follistatin-344 works

Physically binds myostatin and activin with near-irreversible affinity, preventing them from engaging ActRIIB receptors on muscle cells. This blocks downstream ALK4/ALK5 → Smad2/3 signaling that normally suppresses the Akt/mTOR protein synthesis pathway and inhibits satellite cell proliferation.

Also known as: FS-344, FST-344, FS344, Follistatin 344, AAV1-FS344, FS-315

Research relevance

Muscle Growth
Strong research relevance 85
Recovery & Healing
Some relevance 40
Injury Rehab
Some relevance 35
Anti-Aging & Longevity
Some relevance 25

Side effects & safety

No serious adverse events reported in gene therapy trials Injection-site reactions Theoretical hormonal disruption via activin/FSH axis Theoretical tendon vulnerability from rapid muscle growth

Contraindications

Hypersensitivity to AAV1 vector components
Pre-existing immune response to AAV1 capsid proteins
Pregnancy/lactation

Consult a healthcare provider before use if any of these apply to you.

FAQ

What is Follistatin-344? +
A 344-amino-acid glycoprotein that functions as a potent endogenous inhibitor of myostatin (GDF-8) and activin A/B. Tested clinically as an AAV1-delivered gene therapy vector (AAV1.CMV.FS344) for muscular dystrophy, and available as a recombinant peptide through unregulated channels. Its mechanism of action is supported by moderate clinical and preclinical evidence.
What is Follistatin-344 researched for? +
Follistatin-344 has the strongest research relevance for Muscle Growth, Recovery & Healing, Injury Rehab. Evidence is supported by moderate clinical and preclinical evidence.
What are the side effects of Follistatin-344? +
Reported side effects include No serious adverse events reported in gene therapy trials, Injection-site reactions, Theoretical hormonal disruption via activin/FSH axis, Theoretical tendon vulnerability from rapid muscle growth. Key contraindications: Hypersensitivity to AAV1 vector components; Pre-existing immune response to AAV1 capsid proteins; Pregnancy/lactation.
Is Follistatin-344 FDA approved? +
Follistatin-344 is not FDA-approved. It is available as a research compound or through compounding pharmacies in some jurisdictions.
How is Follistatin-344 administered? +
Follistatin-344 is typically administered via subcutaneous route. Researched dosage range: Gene therapy: 3-6 × 10¹¹ vg/kg/leg IM (Mendell et al.); Peptide (unregulated): 100-200 mcg/day SC — not clinically validated. Half-life: Protein: ~90 min (estimated); Gene therapy: sustained expression >15 months in primates (Kota et al., PMID 20368179).

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