# Follistatin 344

> Evidence tier C — Animal data · GH & Growth · reviewed 2026-11-08
> Source page: https://peptidemeta.com/p/follistatin-344/

Also known as: FS-344, Follistatin, FST

## Quick answers

**What is Follistatin 344?**

A recombinant glycoprotein that binds and inhibits myostatin, the primary negative regulator of muscle growth. A ~344-amino-acid glycoprotein (precursor isoform of follistatin) rather than a short peptide.

**How strong is the evidence for Follistatin 344?**

Tier C (animal data) on the peptidemeta evidence scale. Evidence for the protein is from animal studies; the only human data are small open-label gene-therapy trials (AAV-delivered follistatin), not the protein itself.

**Is Follistatin 344 FDA-approved?**

No. Follistatin 344 is not approved by the FDA for any use.

**Is Follistatin 344 banned in sport?**

Yes. Follistatin 344 is prohibited in sport by the World Anti-Doping Agency under S4 (hormone and metabolic modulators).

**How does Follistatin 344 work?**

Follistatin 344 is a recombinant activin-binding protein that sequesters myostatin (GDF-8), activin A, and other TGF-beta superfamily ligands, preventing them from signaling through ActRIIB. By neutralizing myostatin, it removes the primary endogenous brake on skeletal muscle growth, allowing increased muscle fiber hypertrophy and satellite cell-mediated repair.

**What is known about the safety of Follistatin 344?**

Gene therapy trials (AAV-follistatin) showed acceptable safety in muscular dystrophy patients. Recombinant protein form has minimal human safety data.

## Key facts

- **Evidence tier:** C (Animal data)
- **FDA:** not approved
- **WADA:** prohibited (S4)
- **Peptide:** yes
- **Routes studied:** Subcutaneous, Intramuscular

## Overview

A recombinant glycoprotein that binds and inhibits myostatin, the primary negative regulator of muscle growth. Follistatin 344 promotes muscle hypertrophy by removing the myostatin brake.

## Mechanism

Follistatin 344 is a recombinant activin-binding protein that sequesters myostatin (GDF-8), activin A, and other TGF-beta superfamily ligands, preventing them from signaling through ActRIIB. By neutralizing myostatin, it removes the primary endogenous brake on skeletal muscle growth, allowing increased muscle fiber hypertrophy and satellite cell-mediated repair.

## Effects reported in research

_Reported outcomes, not promises; see the evidence tier._

- Myostatin inhibition and muscle growth
- Increased lean muscle mass
- Improved strength output
- Potential bone density enhancement

## Safety & unknowns

Gene therapy trials (AAV-follistatin) showed acceptable safety in muscular dystrophy patients. Recombinant protein form has minimal human safety data. Theoretical risks include disruption of activin/FSH reproductive signaling and fibrosis in non-muscle tissues. Not FDA-approved.

## Status sources

- [Mendell et al. 2015, Mol Ther (AAV follistatin, Becker MD)](https://pubmed.ncbi.nlm.nih.gov/25322757/)
- [WADA 2026 Prohibited List](https://www.wada-ama.org/en/prohibited-list)

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Educational reference only — not medical advice. No dosing information is published. Tiers rate the strength of published evidence, not effectiveness or safety.