# Follistatin > A natural myostatin and activin antagonist — by neutralizing the muscle brake it is one of the most potent pro-muscle factors studied, and a doping and gene-therapy flashpoint. - Also known as: FST, FS-288, FS-315, follistatin-344 - Class: Growth Hormone, Metabolic - FDA approved: No - Canonical page: https://www.americanpeptide.com/catalog/follistatin ## Overview Follistatin is the body’s own counterweight to myostatin. It is a secreted glycoprotein that binds and neutralizes TGF-β-superfamily ligands — most importantly myostatin and activin — and by mopping up the signals that restrain muscle, it becomes one of the most powerful pro-muscle factors in the research literature. If myostatin is the brake on muscle growth, follistatin takes the foot off it. Follistatin exists in the body precisely to oppose the activin/myostatin axis, and overexpressing it produces some of the most striking muscle-growth phenotypes in animal research — larger gains than knocking out myostatin alone, because follistatin blocks multiple inhibitory ligands at once. It occurs in several isoforms (the FS-288 and FS-315 forms differ in how tightly they bind to cell surfaces and heparan sulfate), and as a secreted glycoprotein it is a true biologic, not a synthetic peptide. Most of the serious work on follistatin has been as gene therapy: delivering a follistatin gene (often the FS-344 construct) to muscle has shown durable muscle growth in models and has been explored in early human trials for muscular dystrophies and inclusion-body myositis. That gene-therapy route — rather than injecting the protein — reflects both follistatin’s short half-life and the goal of sustained local expression. It shares the forward-looking metabolic angle with myostatin: as GLP-1-class drugs drive large weight loss that includes muscle, follistatin-based and myostatin-antagonist approaches are part of the strategy to protect lean mass and improve the *quality* of that weight loss. It is, equally, a doping and hype target — "follistatin" products are marketed far beyond the evidence, and the pathway is banned in sport. For a reference, follistatin is best framed honestly: a genuinely potent muscle-growth regulator with real promise in muscle-wasting disease and a real frontier role alongside metabolic drugs — but one whose most credible results come from gene therapy in research settings, not from the supplements and injectables sold under its name. ## Mechanism Binds activin and myostatin with high affinity and sequesters them from their receptors, blocking the ActRIIB/Smad2/3 signaling that suppresses muscle growth. The net effect is disinhibition of muscle-fiber growth, studied as both a protein and a gene-therapy payload. ## Chemistry | Property | Value | | --- | --- | | Molecular weight | 34000 Da | | UniProt | [P19883](https://www.uniprot.org/uniprotkb/P19883) | ## Research areas Studied in: Muscle growth, Muscular dystrophy, Sarcopenia, Body composition, GLP-1 muscle preservation. Guides on this site: - [Longevity & Aging](https://www.americanpeptide.com/research-areas/longevity-aging): Peptides studied across the aging axis — senescence, NAD+, and resilience. - [Growth Hormone & Body Composition](https://www.americanpeptide.com/research-areas/growth-hormone-axis): Secretagogues studied for GH release, IGF-1, and body composition. ## Key research - Potent muscle growth — neutralizing activin and myostatin disinhibits muscle, often exceeding myostatin knockout alone. - Gene therapy — follistatin (FS-344) gene delivery has shown durable muscle growth in models and early human dystrophy/myositis trials. - Muscle-wasting disease — studied across muscular dystrophies, sarcopenia, and cachexia. - GLP-1 muscle preservation — part of the forward-looking strategy to protect lean mass during incretin-driven weight loss. - Multiple isoforms — FS-288 vs FS-315 differ in cell-surface binding and bioavailability. - Doping/hype caution — banned in sport; marketed products run well ahead of the evidence. ## Storage, handling & synthesis **Storage.** Recombinant follistatin is handled as a research glycoprotein — stored frozen as lyophilized powder, kept cold and protected from repeated freeze–thaw after reconstitution. **Handling.** A glycosylated protein sensitive to heat, freeze–thaw, and agitation, which can aggregate it and reduce activity. **Synthesis.** Follistatin is a secreted glycoprotein (isoforms ~31–38 kDa with glycosylation), produced recombinantly in eukaryotic cells rather than by solid-phase synthesis; its mass varies with isoform and glycosylation, so it has no single molecular formula. Much of the credible therapeutic work uses follistatin gene delivery, characterized as a gene-therapy product, with the expressed protein verified by glycoprotein-grade analytics. ## FAQs ### What is follistatin? A secreted glycoprotein that binds and neutralizes myostatin and activin, removing the brakes on muscle growth. It is one of the most potent pro-muscle factors in research, studied mainly as a gene therapy. ### How is follistatin different from myostatin? Myostatin restrains muscle growth; follistatin blocks myostatin (and activin), so it does the opposite. Follistatin can exceed the muscle gains of removing myostatin alone because it neutralizes several inhibitory signals. ### Does follistatin build muscle in humans? The most credible results come from follistatin gene therapy in research and early trials, not from injectable proteins or supplements sold as "follistatin," which run ahead of the evidence. No follistatin therapy is broadly approved. ### Is this medical advice? No — this is a research and educational reference. Follistatin-based approaches are investigational and the pathway is banned in sport. ## Latest research Recent trials and publications mentioning Follistatin, pulled automatically from ClinicalTrials.gov and PubMed (unfiltered search results, refreshed daily). ### Recent trials - [Evaluation of Serum Follistatin-Like Protein 1 Levels in Behcet's Disease and Its Association With Disease Activity](https://clinicaltrials.gov/study/NCT06730958) — COMPLETED · NCT06730958 - [Muscle Vibration as a Countermeasure Against Hypoactivity-induced](https://clinicaltrials.gov/study/NCT07021079) — RECRUITING · NA · NCT07021079 - [Direct Versus Indirect Effect of Amino Acids on Hepatokines](https://clinicaltrials.gov/study/NCT06240039) — ACTIVE_NOT_RECRUITING · NA · NCT06240039 - [A Physical Activity Program to Improve Quality of Life and Reduce Fatigue in Metastatic Breast Cancer](https://clinicaltrials.gov/study/NCT04354233) — COMPLETED · NA · NCT04354233 - [Whey Protein Supplementation in High School Athletes](https://clinicaltrials.gov/study/NCT05589129) — COMPLETED · NA · NCT05589129 - [To studyJUV-161 Administered to Healthy Volunteers Undergoing Unilateral Lower Limb Immobilization (ULLI)](https://clinicaltrials.gov/study/NCT07397468) — RECRUITING · PHASE1, PHASE2 · NCT07397468 --- Source: AmericanPeptide.com — https://www.americanpeptide.com/catalog/follistatin Data license: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Attribution: AmericanPeptide.com. Research reference only — computational and educational content, not medical advice.