← All compounds · evidence tier first, by design
| Use | E1 | E2 | E3 | E4 | E5 | E6 | E7 | E8 |
|---|---|---|---|---|---|---|---|---|
| E4 Muscle disease via follistatin-344 gene therapy (a different intervention) | E4 | |||||||
| E8 Muscle growth and strength (injected follistatin-344 protein) | E8 |
Follistatin-344
An alternatively spliced isoform of human follistatin, a cysteine-rich secreted glycoprotein rather than a short peptide. Black-market products analysed in 2019 contained a His-tagged recombinant protein with a high proportion of oligomers.
Non-standard residues or modifications: no plain one-letter sequence
Also: Follistatin 344, FS344, FST344
A form of follistatin, a natural protein that binds and blocks myostatin and related growth factors that limit muscle growth. Gray-market vials labelled "follistatin 344" are sold for muscle building. That is different from the clinical research, which used a gene-therapy virus carrying the follistatin-344 gene, injected into the thigh muscles of a few patients with muscular dystrophy or inclusion body myositis. No follistatin product is approved as a medicine in any jurisdiction checked.
- US C gray market
- EU ? not verified
- UK ? not verified
- CA ? not verified
- AU ? not verified
- JP ? not verified
- CN ? not verified
01Regulatory status, by jurisdiction
| Jurisdiction | Status | Detail and primary source |
|---|---|---|
| US | Not approved | No FDA-approved follistatin product was identified; the black-market analysis cited above also states that no approved pharmaceutical formulations of follistatin are available. Follistatin does not appear in any category (1, 2 or 3) of FDA's list of bulk drug substances nominated for 503A compounding, updated 14 May 2026, so it has not been nominated for pharmacy compounding.“Includes three categories of bulk drug substances: Category 1: Bulk Drug Substances Under Evaluation Category 2: Bulk Drug Substances that Raise Significant Safety Concerns Category 3: Bulk Drug Substances Nominated Without Adequate Support”Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the Federal Food, Drug, and Cosmetic Act (Updated May 14, 2026) · retrieved 2026-10-10 |
| EU UK CA AU JP CN | Not yet verified from a primary source. No status is shown rather than an unsourced one. | |
Sport (WADA): Prohibited · class S4.3. Named as a myostatin-binding protein under class S4.3 (agents preventing activin receptor IIB activation), prohibited at all times, on the 2026 Prohibited List. “Myostatin inhibitors such as: Agents reducing or ablating myostatin expression Myostatin-binding proteins (e.g. follistatin, myostatin propeptide)” WADA source
02What the human evidence shows
Muscle disease via follistatin-344 gene therapy (a different intervention)
No randomised controlled trial in humans has been published for this use.
Gene therapy is not the gray-market product. An adeno-associated virus carrying the follistatin-344 gene was injected into the thigh muscles of six men with Becker muscular dystrophy and, separately, six people with sporadic inclusion body myositis. Walking distance improved in four of six in each study, with no adverse effects reported; the myositis study compared against eight untreated patients, not a randomised control. In macaques, the same vector increased muscle size and strength.
- [1] Uncontrolled trial in six patients with Becker muscular dystrophy; four improved on the six-minute walk test
- [2] Six treated patients with inclusion body myositis compared with eight untreated matched patients on six-minute walk distance
- [3] Increased quadriceps size and strength in cynomolgus macaques after intramuscular AAV1-FS344 gene transfer
Registered-study counts: ClinicalTrials.gov intervention search “follistatin”, fetched 2026-10-10. Registered studies include trials of other uses; the gap between registered and reported is itself a finding.
Muscle growth and strength (injected follistatin-344 protein)
No human trial of any design has been published for this use.
No published study of injected follistatin-344 protein in any model, animal or human, was identified. Animal studies of follistatin protein used other forms: an engineered follistatin-315 fusion protein increased lean mass in mice, while follistatin-288 protein in rats had mixed effects, including smaller muscles and less force in some groups. These results cannot be transferred to gray-market follistatin-344, whose stability, activity and content are unknown.
- [4] An engineered follistatin-315 Fc fusion protein (not follistatin-344) increased lean muscle mass in mice
- [5] Follistatin-288 protein (not follistatin-344) had mixed effects on muscle weight and force in rats after nerve injury
Registered-study counts: ClinicalTrials.gov intervention search “follistatin”, fetched 2026-10-10. Registered studies include trials of other uses; the gap between registered and reported is itself a finding.
Key registered trials
| NCT | Title (as registered) | Phase | Status |
|---|---|---|---|
| NCT01519349 | Follistatin Gene Transfer to Patients With Becker Muscular Dystrophy and Sporadic Inclusion Body Myositis | 1 | Completed |
| NCT02354781 | Clinical Intramuscular Gene Transfer of rAAV1.CMV.huFollistatin344 Trial to Patients With Duchenne Muscular Dystrophy | 1/2 | Completed |
03Safety signals
There are no adequate human safety data. The absence of reported harm is not evidence of safety.
- Mislabelled and uncharacterised black-market products [6]
In an anti-doping laboratory analysis of 17 black-market products sold as follistatin, only nine contained follistatin; some others contained different growth-promoting peptides. All nine follistatin-containing products held a His-tagged recombinant protein with a high degree of oligomers.
04What is unknown
- No human or animal study of injected follistatin-344 protein was identified, for efficacy, pharmacokinetics or safety
- Whether injected recombinant follistatin-344 protein stays active long enough in the body to affect muscle is unknown
- Follistatin also binds activins, which act in reproductive and other tissues; effects of systemic exposure in humans are unstudied
- Immunogenicity of His-tagged, partly oligomerised black-market protein has not been assessed
- The gene-therapy findings come from 12 patients without randomised controls and do not apply to protein injections
- Regulatory status outside the US was not verified from regulator sources for this record
05Product quality
No independent purity results have been published for this compound yet. The purity programme will publish full methods and vendor-named results, passes and failures, once its protocol has had legal review.
06Citations
- A phase 1/2a follistatin gene therapy trial for becker muscular dystrophy (2015). doi:10.1038/mt.2014.200
- Follistatin Gene Therapy for Sporadic Inclusion Body Myositis Improves Functional Outcomes (2017). doi:10.1016/j.ymthe.2017.02.015
- Follistatin gene delivery enhances muscle growth and strength in nonhuman primates (2009). doi:10.1126/scitranslmed.3000112
- Follistatin: a novel therapeutic for the improvement of muscle regeneration (2014). doi:10.1124/jpet.113.211169
- Follistatin Protein Enhances Satellite Cell Counts in Reinnervated Muscle (2022). doi:10.1055/s-0042-1748535
- Detection of black market follistatin 344. doi:10.1002/dta.2741
Every DOI is resolved against Crossref and every NCT number against ClinicalTrials.gov, title for title, before publication. Regulatory sources are cited inline above with a verbatim quote and retrieval date.
07Mechanism
Follistatin binds myostatin and activins and blocks their signalling through activin type II receptors; in mice and macaques, raising follistatin levels by gene transfer increased skeletal muscle size.
Mechanism is placed last on purpose: a plausible mechanism is not evidence that a compound works in people.
Reviewed by OSMF research team (AI-assisted, source-verified) on 2026-10-10. Found an error? It goes in the corrections log: report it.