Wellness and performance
Bones & muscles
Follistatin-344
Also called FST-344
Follistatin-344 is a myostatin-binding protein sold for muscle gain. See how it works, why it is not FDA-approved, and what human research exists.
- Reviewed by
- William Maish, MD MBA MPH, Clinical Product Lead
- Published
- October 5, 2026
- Last updated
- October 5, 2026
Key takeaway
Follistatin-344 is a form of the natural protein follistatin that blocks myostatin, a brake on muscle growth, sold as a "research chemical" in the performance market for muscle gain. The strongest human data come from gene therapy, not the injectable peptide. In a small 2017 trial, six patients with sporadic inclusion body myositis gained a median 56.0 m per year on the 6-minute walk test after follistatin gene therapy, versus a 25.8 m decline in eight matched untreated controls (p = 0.01). It is not FDA-approved and is banned in sport.
At a glance
| FDA status | Non-FDA-approved peptide sold as a research chemical/performance drug |
| What it is | Myostatin-binding protein, marketed to remove a natural brake on muscle growth |
| Research | Human data come only from small gene-therapy disease trials, not the injectable peptide |
| Sport | Prohibited by WADA at all times |
| Evidence strength | Low research |
What is follistatin-344?
Follistatin is a natural protein that binds and neutralizes myostatin and related factors. Follistatin-344 (FS344) refers to a specific 344-amino acid form used in research and gene-therapy work. In the performance market, an injectable "follistatin peptide" is sold for muscle growth, though it is a different, uncharacterized product from the gene-therapy material. It is not an approved medicine.
How does it work?
Myostatin normally limits how much muscle the body builds. By binding and neutralizing myostatin, follistatin is proposed to release that brake and allow greater muscle growth. This pathway is well supported in animal models1, where disrupting myostatin signaling produces pronounced muscle growth. This describes the proposed mechanism, which comes from animal work, separate from proven outcomes in people using the injectable peptide.
Is it FDA-approved?
No. Follistatin-344 is not approved by the FDA as a drug. Its status by form and setting:
- Injectable peptide: a research chemical and performance-enhancing drug with no recognized compounding status
- Gene therapy: remains investigational
- Sport: myostatin-binding proteins including follistatin are prohibited at all times under the WADA list
What does the research show?
The human evidence belongs to gene therapy, not the peptide. According to PubMed, a small Phase 1/2a trial2 used a gene therapy delivering the follistatin (FS344) gene in six patients with Becker muscular dystrophy, reporting some walking improvements and muscle changes; follow-up3 reported ambulation data. This is a disease population and a gene-therapy delivery, not the injectable follistatin peptide sold for wellness, and it does not establish efficacy or safety of that peptide in healthy people. There are no controlled human trials of the injectable peptide.
Two small studies of this gene therapy report walking results:
| Study | Patients | Design | Result |
| Phase 1/2a trial in Becker muscular dystrophy | 6 treated | No placebo group | 4 of the 6 walked farther on the 6-minute walk test, by 29 m to 125 m4; muscle biopsies showed less fibrosis |
| Study in sporadic inclusion body myositis5, an inflammatory muscle disease, published in 2017 | 6 treated, versus 8 matched, untreated controls | Same gene therapy alongside an exercise regimen; controls not randomized | Treated patients gained a median 56.0 m per year on the 6-minute walk test, versus a 25.8 m decline in controls (p = 0.01), with individual changes of 5 to 153 m |
The 2017 sample was tiny and the controls were not randomized, so that result is hypothesis-generating.
More for bones & muscles
Sources: a Phase 1/2a follistatin gene-therapy trial (Mendell et al., Molecular Therapy, 2014, DOI: 10.1038/mt.2014.2002) and its follow-up (Journal of Neuromuscular Diseases, 2015, DOI: 10.3233/jnd-1500833), indexed on PubMed; and the WADA Prohibited List. This document is educational, is not medical advice or a health claim, and is not an offer to sell any product.