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Follistatin: what the research shows, and what it doesn’t

By Pinnacle Pulse Editorial Team · Status as of 16 October 2026 · Next scheduled update: 14 January 2027

Short answer: Follistatin is a protein the body makes that, among other things, blocks myostatin, a brake on muscle growth. It is not a short peptide, and the serious research on it is about gene therapy. Small, uncontrolled trials in two muscle diseases reported mixed but partly encouraging walking results. No approved follistatin medicine exists.

What follistatin is

Follistatin got its name from its first known job. It was identified as a protein that suppresses follicle-stimulating hormone, FSH, by binding activin, one of the signals that controls the pituitary. It is made in many tissues and circulates in the blood.

Its fame in muscle biology came later, through myostatin. Myostatin tells muscles to stop growing; animals born without it are unusually muscular. In 2001 Se-Jin Lee and Alexandra McPherron at Johns Hopkins showed in PNAS that follistatin can stop myostatin from binding its receptor. Mice engineered to make large amounts of follistatin in their muscles had “dramatic increases in muscle mass”, similar to mice lacking myostatin entirely.

Two points matter for reading anything else about it. Follistatin is a full protein, several hundred amino acids long, far larger than the peptides on the rest of this site. And because it also binds activin, it touches reproductive hormones, which is why researchers were cautious about giving it to people.

What has been studied

Gene therapy in monkeys

A team at Nationwide Children’s Hospital in Columbus, Ohio, chose a different route than injecting the protein. They packed the gene for one particular form of follistatin, called FS344, into a harmless virus (AAV1) and injected it directly into thigh muscle, so that muscle cells would make the protein themselves. FS344 was picked because it acts mainly on muscle and binds activin less tightly than other forms.

In cynomolgus macaques, reported in Science Translational Medicine in 2009, this produced pronounced and lasting increases in muscle size and strength, and the researchers found no abnormal changes in key organs. The paper discloses that two senior authors and the hospital had filed a provisional patent on the approach. An erratum to the paper was published in 2026.

Two small trials in patients

The same group then moved to people with muscle diseases that have little or no treatment.

In Becker muscular dystrophy, six patients received the gene therapy in both thighs (Molecular Therapy, 2015). The main measure was how far they could walk in six minutes. Four improved, by between 29 and 125 meters. Two showed no change. There was no placebo group. The authors reported no adverse effects and found less scarring in muscle biopsies.

In sporadic inclusion body myositis, a slowly progressive muscle disease of older adults, six patients were treated and compared with eight untreated patients matched for age, sex and baseline walking (Molecular Therapy, 2017). All took part in an exercise program as well. Treated patients walked further over a year while the comparison group declined. Four of the six improved substantially; two barely changed. The comparison group was not randomized, and the exercise program complicates the picture.

What has happened since

ClinicalTrials.gov also lists three open-label, uncontrolled studies of follistatin gene therapy in healthy volunteers, run by private sponsors outside the academic setting described above. None of them has posted results there.

What the research does not show

The human data come from twelve treated patients across two small trials, without randomized controls, all with serious muscle diseases. They don't show a benefit for healthy people, and they don't show a benefit large or consistent enough to make this a treatment yet.

They don’t show long-term safety. Gene therapy can’t simply be stopped once given, and the trials followed patients for a limited time.

They say nothing about injecting follistatin protein or anything sold online under the name “follistatin”, and a product labelled that way may contain something else entirely.

And the hormone question is not settled. Follistatin binds activin, which helps regulate FSH. The trials used a form chosen to reduce that effect, not to remove it.

Status as of 16 October 2026. EU and US: no follistatin medicine or follistatin gene therapy is authorized. EMA’s medicines data and Drugs@FDA have no entry, and FDA’s list of approved cellular and gene therapy products doesn’t include one. WADA: the 2027 Prohibited List names myostatin-binding proteins, for example follistatin, under S4.3, prohibited at all times. Gene transfer is separately banned as gene doping under M3.

FAQ

Is follistatin a peptide?

Not in the usual sense. It is a full protein, much larger than peptides such as BPC-157 or ipamorelin. Its serious medical research has focused on delivering the follistatin gene into muscle.

Has follistatin been tested in humans?

In two small academic gene-therapy trials, in Becker muscular dystrophy and inclusion body myositis, with six treated patients each. Neither had a randomized control group.

Why is follistatin banned in sport?

WADA lists follistatin by name as a myostatin-binding protein under class S4.3. Delivering it by gene transfer would also fall under the ban on gene doping.

Sources

  • Lee SJ, McPherron AC. Regulation of myostatin activity and muscle growth. Proc Natl Acad Sci U S A. 2001;98(16):9306-11. PMID 11459935
  • Kota J, et al. Follistatin gene delivery enhances muscle growth and strength in nonhuman primates. Sci Transl Med. 2009;1(6):6ra15. PMID 20368179 (erratum 2026)
  • Mendell JR, et al. A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy. Mol Ther. 2015;23(1):192-201. PMID 25322757
  • Al-Zaidy SA, et al. Follistatin gene therapy improves ambulation in Becker muscular dystrophy. J Neuromuscul Dis. 2015;2(3):185-192. PMID 27858738
  • Mendell JR, et al. Follistatin gene therapy for sporadic inclusion body myositis improves functional outcomes. Mol Ther. 2017;25(4):870-879. PMID 28279643
  • ClinicalTrials.gov. NCT01519349, follistatin gene transfer in Becker muscular dystrophy and inclusion body myositis. clinicaltrials.gov
  • WADA. 2027 Prohibited List, classes S4.3 and M3. wada-ama.org
  • ClinicalTrials.gov. NCT06411366, NCT07285629 and NCT07443826, follistatin gene therapy studies in healthy volunteers (no results posted), checked 16 October 2026. clinicaltrials.gov
  • EMA. Download medicine data: table of all medicines assessed by EMA (Excel), checked 16 October 2026. ema.europa.eu
  • FDA. Drugs@FDA, database of FDA-approved drugs, checked 16 October 2026. accessdata.fda.gov
  • FDA. Approved cellular and gene therapy products, checked 16 October 2026. fda.gov

Facts last checked: 16 October 2026.

About this article

Written by: the Pinnacle Pulse Editorial Team, the people who make the Pinnacle Pulse app. We work only from primary sources such as regulators, legal texts, trial registries and PubMed, and we remove claims we can’t check against one.

This article has not been reviewed by a physician. It is general information, not medical advice.

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Change log

  • 16 October 2026: First published.

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