{"id":"follistatin-344","name":"Follistatin 344","aliases":["FS344","follistatin","FST-344","myostatin inhibitor"],"url":"https://lyoresearch.com/compounds/follistatin-344","class":{"id":"growth-hormone-and-igf","name":"Growth hormone, IGF-1 and growth factors","url":"https://lyoresearch.com/classes/growth-hormone-and-igf"},"summary":"Follistatin is a natural protein that binds and blocks myostatin, the signal that limits muscle growth; animals engineered to overexpress it become dramatically muscular. 'Follistatin 344' is the full-length form, sold as a lyophilised injectable for muscle. No human trial has ever tested injecting it. The only clinical data is a 2015 gene-therapy study in six men with Becker muscular dystrophy, in which a virus carrying the follistatin gene was injected into the thigh muscles — some walked further, some did not, and it is not the product being sold. It is prohibited in sport.","overall_grade":"D","overall_grade_meaning":"no human evidence","human_trials":"0 for the injected protein; 1 gene-therapy trial (n=6)","regulatory_status":"Not approved; research reagent","molecule":{"formula":null,"molecular_weight":null,"cas":null,"pubchem_cid":null,"note":"A 344-residue glycoprotein — no small-molecule record"},"pharmacokinetics":{"basis":"none","route":"Injected as sold; no human study of the peptide","half_life":"No human pharmacokinetic data","licensed_regimen":null,"product":null,"source":null},"outcomes":[{"outcome":"Muscle growth / strength (injected protein)","grade":"D","grade_meaning":"no human evidence","effect_size":"not measurable","adverse":false,"human_studies":"0 controlled","evidence":"No human study of any kind has given follistatin protein by injection. The grey-market product has no clinical file, and a 344-residue glycoprotein injected subcutaneously would be expected to be cleared quickly and to bind targets far beyond muscle.","references":[{"citation":"Searches of PubMed and trial registries for injected follistatin in humans.","where":"LYO literature search, September 2026","url":"https://pubmed.ncbi.nlm.nih.gov/?term=follistatin+injection+human+trial+muscle"}]},{"outcome":"Muscle function in Becker muscular dystrophy (gene therapy)","grade":"D","grade_meaning":"no human evidence","effect_size":"small","adverse":false,"human_studies":"1 open-label phase 1/2a (n=6)","evidence":"A follistatin gene delivered by AAV into the quadriceps of six patients: four walked further on the six-minute test, two did not change, with no control group. Encouraging as proof of principle; not evidence for the injected protein, and not evidence in healthy people.","references":[{"citation":"Mendell JR, Sahenk Z, Malik V, et al. A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy.","where":"Mol Ther, 2015","url":"https://pubmed.ncbi.nlm.nih.gov/25322757/"}],"verbatim":{"text":"AAV1.CMV.FS344 was delivered to six BMD patients by direct bilateral intramuscular quadriceps injections.","citation":"Mendell JR, Sahenk Z, Malik V, et al. A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy.","url":"https://pubmed.ncbi.nlm.nih.gov/25322757/"}},{"outcome":"Fat loss","grade":"D","grade_meaning":"no human evidence","effect_size":"not measurable","adverse":false,"human_studies":"None","evidence":"Claimed on the basis of myostatin-knockout animals; no human data.","references":[]},{"outcome":"Safety in humans","grade":"D","grade_meaning":"no human evidence","effect_size":"not measurable","adverse":true,"human_studies":"None for the protein","evidence":"Follistatin also neutralises activin, which regulates reproduction, inflammation and the pituitary. Systemic blockade in humans has never been characterised. The gene-therapy trial reported no adverse effects in six people over a limited follow-up — in muscle-restricted delivery.","references":[]}],"regions":[{"region":"European Union","status":"Unauthorised medicinal product","note":"No marketing authorisation anywhere. Supplying it for human use is an offence under national medicines law."},{"region":"United States","status":"Not approved","note":"Sold as a research reagent 'not for human use'; no clinical programme for the protein."},{"region":"United Kingdom","status":"Unlicensed medicine","note":"No MHRA licence; supply for human use is an offence."},{"region":"Australia","status":"Prescription-only / unapproved","note":"Not on the ARTG; imports are seized."},{"region":"Canada","status":"Not authorised","note":"No Drug Identification Number."},{"region":"Sport (WADA)","status":"Prohibited at all times","note":"Myostatin inhibitors are prohibited under the S4 class (agents preventing activin receptor IIB activation), in and out of competition."}],"faq":[{"q":"Does follistatin 344 build muscle?","a":"In animals engineered to make more of it, dramatically. In humans, no trial has tested injecting it, so the honest answer is unknown — and the six-patient gene-therapy study people cite used a virus to make muscle produce it locally, which is a different intervention."},{"q":"Is the gene-therapy trial evidence for the injection?","a":"No. Local, continuous production inside the muscle from a delivered gene is not the same as a protein injected under the skin, which is cleared quickly and acts everywhere. The trial also had six patients and no control group."},{"q":"Is follistatin safe?","a":"Unknown. It blocks activin as well as myostatin, and activin does many things — including in reproduction. No one has measured what happens when it is blocked systemically in people."}],"references":[{"cite":"Mendell JR, Sahenk Z, Malik V, et al. A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy.","where":"Mol Ther, 2015","url":"https://pubmed.ncbi.nlm.nih.gov/25322757/","note":"Six patients; AAV1.CMV.FS344 injected into the quadriceps; no control group."},{"cite":"Searches of PubMed and trial registries for injected follistatin in humans.","where":"LYO literature search, September 2026","url":"https://pubmed.ncbi.nlm.nih.gov/?term=follistatin+injection+human+trial+muscle","note":"No human trial of the injected protein identified."},{"cite":"World Anti-Doping Agency. The Prohibited List — S4: hormone and metabolic modulators.","where":"WADA, current list","url":"https://www.wada-ama.org/en/prohibited-list","note":"Myostatin inhibitors / agents preventing activin receptor IIB activation."}],"last_reviewed":"2026-09-10","literature_searched_to":"2026-09-10","changelog":[{"date":"2026-09-10","note":"Initial publication. Grade D on absence of any human trial of the injected protein; the gene-therapy study is described and separated."}],"license":"CC BY 4.0 — cite as “LYO Research” with a link.","methodology":"https://lyoresearch.com/methodology"}