Peptide Evidence Index

Follistatin

Evidence last reviewed: September 2026

Quick answers

What is it?: Follistatin is a protein the body already makes that blocks myostatin, a signal that normally limits muscle growth. What's sold online as an injectable "follistatin peptide," however, has never been tested in any human trial; every human study used a gene therapy that makes the body produce its own follistatin instead.
Why are people interested in it?: It's marketed for muscle building and anti-aging, so people want to know whether the follistatin gene-therapy results in muscle-disease patients say anything about the injectable protein product sold online.
What has actually been studied?: A small Becker muscular dystrophy gene-therapy trial (6 patients), a small Duchenne muscular dystrophy trial, and three more recent offshore trials in healthy adults run in Honduras, none of which tested the injectable protein product itself.
How strong is the evidence?: Early human data at best, and only for a completely different product (gene therapy) than what's sold as "follistatin peptide." No trial of the injectable protein exists at any dose.
What don't we know yet?: Whether the injectable follistatin protein sold online has ever been tested in a human at any dose, and what the completed offshore gene-therapy trials in healthy adults actually found; none have posted results.
Where can I read the original research?: Sources at the bottom of this page: Mendell et al., Molecular Therapy 2015 (the Becker muscular dystrophy trial); ClinicalTrials.gov NCT06411366 (Minicircle, Honduras).

Plain-English overview

Follistatin is a protein the human body already makes, whose main job is to block myostatin, a signal that normally limits muscle growth. What is sold online as an injectable "follistatin peptide" is not the same product that has ever been tested in a human being; every human trial identified used a gene therapy, a viral vector or DNA plasmid injected into muscle that instructs the body's own cells to manufacture follistatin internally. Neither the gene therapy nor the injectable protein is approved as a medicine anywhere. The most substantial human results come from a small trial in Becker muscular dystrophy patients; more recent trials have moved to healthy adults but were run at clinics in Honduras structured to sit outside conventional US and EU medical regulation, and none of those recent trials has posted results.

What researchers are studying it for

Becker muscular dystrophy
Duchenne muscular dystrophy
sporadic inclusion body myositis
general muscle mass, strength, and biological aging markers (small, offshore, unregulated-jurisdiction trials)

Current evidence level

Early human data

Regulatory status: Not an approved medicine. Evidence strength and approval are scored separately; approval is a regulatory decision about a specific use, not a measure of how much research exists.

Human research

Five follistatin gene-therapy trials could be identified, and none tested the injectable protein product marketed online. The most substantial is a Phase 1/2a trial published in Molecular Therapy in 2015, in which six Becker muscular dystrophy patients received a single intramuscular injection of an AAV-delivered follistatin gene (FS344) into their thigh muscles at one of two doses; four of the six improved their distance on a six-minute walk test by between 29 and 125 meters, with no adverse effects reported, and muscle biopsies showed less scarring and larger muscle fibers, especially at the higher dose, while two of the six patients showed no improvement. A companion review in the Journal of Neuromuscular Diseases describes the same trial and its broader biology. A separate Phase I/II trial in three Duchenne muscular dystrophy patients (NCT02354781) has posted results directly to its ClinicalTrials.gov entry, while an earlier Phase I trial combining Becker muscular dystrophy and sporadic inclusion body myositis patients (NCT01519349, n=15) completed in 2017 without posting results. Since 2022, a company called Minicircle has run several small follistatin gene-therapy trials in healthy adults broadly interested in muscle, aging, and biological-age markers, at clinics in Roatan and the Prospera economic zone in Honduras; the largest (NCT06411366) enrolled 43 adults and completed in 2023, and a second (NCT07285629, n=14) tested a combined klotho-and-follistatin gene therapy and completed in 2026, neither has posted results, and a third (NCT07443826, n=12) was still recruiting as of this review. No human trial, of the protein or the gene therapy, has tested follistatin in a healthy adult for the reason it is most often marketed today: general muscle-building or fat-loss use outside a medical or research setting.

Animal and preclinical research

Trial reports describe "extensive preclinical studies" using AAV-delivered follistatin that demonstrated increased strength in animal models, laying the groundwork for the human Becker muscular dystrophy trial. This review did not identify a distinct, separately citable animal efficacy study beyond that groundwork description.

Major findings

In a Phase 1/2a trial published in 2015, four of six Becker muscular dystrophy patients who received a single injection of AAV-delivered follistatin gene therapy improved their six-minute-walk-test distance by 29 to 125 meters, with muscle biopsies showing less scarring and larger fibers.
Two of the six Becker muscular dystrophy patients in that trial showed no improvement, and no adverse effects were reported at either dose tested.
A separate Duchenne muscular dystrophy gene-therapy trial (n=3) has posted results directly to its ClinicalTrials.gov entry.
Since 2022, a company called Minicircle has run follistatin gene-therapy trials in healthy adults, not muscle-disease patients, at clinics in Honduras structured to sit outside conventional US and EU regulation.
The largest of those offshore trials enrolled 43 healthy adults and completed in 2023; as of this review, more than two years later, no results have been posted.
No human trial has ever tested the injectable follistatin protein product sold online as "follistatin peptide"; every human trial used a fundamentally different gene-therapy product.
No human trial has tested follistatin, in any form, for general muscle-building or fat-loss use in healthy adults outside a research or medical setting.

What has not been established

Whether the injectable "follistatin peptide" protein sold online has ever been tested in a human being, at any dose, for any purpose.
What the completed Minicircle gene-therapy trials in healthy adults actually found; none of their results have been posted.
Whether a treatment developed for rare, severe muscle-wasting disease carries the same risk-benefit balance in a healthy person seeking more muscle.
What long-term effects a permanent or long-lasting gene-therapy change to the myostatin pathway has, since the longest published follow-up runs to about two years.
Why several recent follistatin trials are being run specifically in a jurisdiction structured to sit outside conventional medical regulation.

Important limitations

The only published efficacy data come from a six-patient trial in a specific, rare muscle disease, far too small to generalize, and not conducted in healthy adults.
Every trial relevant to today's marketing claims (healthy adults, muscle building, anti-aging) has been run offshore in Honduras and has not posted results.
The product actually studied (gene therapy) is fundamentally different from the injectable protein sold online, so none of this human evidence describes dosing, safety, or effectiveness of that product.
Two of six patients in the pivotal Becker muscular dystrophy trial showed no improvement, meaning the effect was not universal even in the population it was designed for.
No control or placebo group was used in the six-patient Becker trial, limiting how confidently the improvement can be attributed to the treatment itself.

Regulatory status

Follistatin gene therapy is not approved as a medicine anywhere, and every human trial identified is early-phase (Phase 1 or 1/2a) or a small pilot. Several recent trials were conducted at clinics in Honduras, including the Prospera economic zone, specifically structured to operate outside FDA and most conventional medical regulation. The injectable follistatin protein sold online as "follistatin peptide" is a materially different, entirely untested product with no human trial data of any kind.

Primary research sources

Mendell JR, Sahenk Z, Malik V, et al., "A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy": Molecular Therapy 2015;23(1):192-201; PMID 25322757, DOI 10.1038/mt.2014.200
Al-Zaidy SA, Sahenk Z, Rodino-Klapac LR, Kaspar B, Mendell JR, "Follistatin Gene Therapy Improves Ambulation in Becker Muscular Dystrophy": Journal of Neuromuscular Diseases 2015;2(3):185-192; PMID 27858738, DOI 10.3233/JND-150083
"Phase I Clinical Intramuscular Gene Transfer of rAAV1.CMV.huFollistatin344 Trial to Patients With Becker Muscular Dystrophy and Sporadic Inclusion Body Myositis": ClinicalTrials.gov NCT01519349, n=15, completed 2017, no results posted
"Phase I/II Clinical Intramuscular Gene Transfer of rAAV1.CMV.huFollistatin344 Trial to Patients With Duchenne Muscular Dystrophy": ClinicalTrials.gov NCT02354781, n=3, completed 2017, results posted
"A Phase I, Open Label, Single Dose Study to Evaluate the Safety and Efficacy of an Injectable Follistatin Plasmid Gene Therapy in Healthy Subjects": ClinicalTrials.gov NCT06411366, Minicircle, n=43, completed 2023 in Roatan, Honduras, no results posted
"Evaluating the Safety and Efficacy of Injectable Combination Klotho and Follistatin Plasmid Gene Therapy in Humans": ClinicalTrials.gov NCT07285629, Minicircle, n=14, completed 2026 in Honduras, no results posted
"CALM-AF-AI: Counteracting Age-related Loss of Muscle With AAV-Follistatin Combined With Angiogenesis-Inducing VEGF Plasmid Gene Therapy": ClinicalTrials.gov NCT07443826, n=12 (recruiting), Prospera ZEDE, Honduras

Full evidence entry (complete data, registry records, dosing evidence)

Early human data

Small or uncontrolled human studies only

At a glance

Also known as: FS344, Follistatin-344, AAV1.CMV.huFollistatin344 (the form actually studied in trials)
Class: Naturally occurring glycoprotein; the version studied in human trials is not the protein itself but a gene therapy that directs the body to produce it
Derived from: A protein the body already makes, which blocks myostatin — a signal that normally limits muscle growth. The version tested in humans is not injected as a protein; it is delivered as an AAV viral vector or a DNA plasmid carrying the gene for an alternatively spliced variant (FS344), chosen because it binds a related hormone-signaling pathway less than other variants
Registered human trials: 5
…with published results: 2
Largest human trial: 43 healthy adults (Minicircle, completed 2023, Roatán, Honduras) — a single injection of follistatin plasmid gene therapy, administered outside FDA jurisdiction; safety and change in blood follistatin levels were measured, and no results have been posted more than two years after completion
Studied for: Becker muscular dystrophy, Duchenne muscular dystrophy, sporadic inclusion body myositis, general muscle mass, strength, and biological aging markers (small, offshore, unregulated-jurisdiction trials)
Dosing evidence: No human dose establishedNo dose has ever been studied for the injectable recombinant-protein product sold online as 'follistatin peptide.' The only human dosing data covers a fundamentally different product — a gene therapy, dosed in viral or plasmid copies rather than micrograms of protein — tested in a small number of patients with specific muscle diseases or in offshore clinics.
Regulatory status: Not approved as a medicine or gene therapy anywhere. Every human trial identified is early-phase (Phase 1 or 1/2a) or a small pilot, and several were conducted at a clinic in Honduras specifically to operate outside FDA jurisdiction. This is a materially different product from the injectable protein marketed as 'follistatin peptide' online, which has no human trial data of any kind.
Anti-doping status: Myostatin-pathway inhibitors and gene- or cell-doping methods are named categories on the World Anti-Doping Agency's prohibited list; this review did not verify a record naming follistatin specifically, so this status should be treated as a general category match rather than a confirmed, compound-specific citation.

What it is

Follistatin is a protein the human body already makes. Its main job is to block myostatin, a signal that normally puts the brakes on muscle growth — which is why blocking it has long been of interest for muscle-wasting disease and, separately, for people who want more muscle.

Here is the distinction that matters most: the "follistatin" sold online as an injectable peptide is not the same thing that has been tested in any human trial. Every human study identified in this review used a gene therapy — a viral vector or DNA plasmid injected into muscle or under the skin, carrying instructions for the body's own cells to manufacture follistatin internally. That is a fundamentally different product, delivery method, and risk profile from injecting recombinant follistatin protein directly, which is what most gray-market vials claim to contain.

Neither product is approved as a medicine anywhere.

What the studies actually found

The most substantial human results come from a small Becker muscular dystrophy trial: six patients received a single intramuscular injection of an AAV-delivered follistatin gene into their thigh muscles, at one of two doses. In the published results, four of the six patients improved their distance on a six-minute walk test — by between 29 and 125 meters — with no adverse effects reported, and muscle biopsies showed less scarring and larger muscle fibers, especially at the higher dose. Two of the six patients showed no improvement. That is a real, if small and uncontrolled, signal in a specific disease population — not a healthy-adult performance study.

More recent trials shift the picture. Since 2022, a company called Minicircle has run several small follistatin gene-therapy trials — not in muscle-wasting disease patients, but in adults broadly interested in muscle, aging, and biological-age markers — at a clinic in Roatán, Honduras, and, most recently, in a jurisdiction in Honduras called Próspera that is specifically structured to sit outside US and most conventional medical regulation. These trials measure blood follistatin levels, body composition, and a battery of aging and inflammation markers. As of this review, the completed trials in this group have not posted their results — in one case, more than two years after the trial finished.

What exists in humans

Five follistatin gene-therapy trials could be identified: two in specific, rare muscle diseases (Becker muscular dystrophy and Duchenne muscular dystrophy, run at Nationwide Children's Hospital in the US), and three run more recently by biotech companies in offshore Honduran clinics, in adults without a diagnosed muscle-wasting disease. The Becker trial's results were published in a peer-reviewed journal. The Duchenne trial has results posted directly to its registry entry. The three more recent Honduras based trials are either completed with no results posted, or still recruiting.

No human trial — of the protein or the gene therapy — has tested follistatin in a healthy adult population for the primary reason it's marketed today: general muscle-building or fat-loss use in otherwise healthy people outside a medical or research setting. The Minicircle trials come closest, but their results are not yet public.

What doses have been studied in humans

Every dose that has been studied in a human trial was a gene-therapy dose — measured in vector genomes or plasmid copies per kilogram of body weight, injected once into muscle tissue or under the skin, not a repeated injection of follistatin protein. In the Becker trial, patients received one of two fixed doses, delivered as a single treatment into each thigh, with follow-up over two years to track walking distance, muscle biopsies, and safety. The more recent Honduras-based trials likewise used a single administration, followed by blood tests over roughly three months.

None of this tells you anything about dosing an injectable follistatin protein product, which is what is actually sold as "follistatin peptide" online. No such product has been tested in a human trial at any dose. Any dosing information circulating for that product does not come from a published human study of the injectable protein — it typically comes from unrelated animal research or from extrapolating the very different gene-therapy dosing described above, neither of which estimates effectiveness or safety for a chronically self-injected protein.

What remains unknown

Whether the injectable "follistatin peptide" protein sold online has ever been tested in a human being, at any dose, for any purpose
What the completed Minicircle gene-therapy trials in healthy adults actually found — none of their results have been posted
Whether a treatment aimed at rare, severe muscle-wasting diseases carries the same risk-benefit balance in a healthy person seeking more muscle
What long-term effects a permanent or long-lasting gene-therapy change to the myostatin pathway has, since the longest published follow-up is measured in months to a couple of years
Why several recent follistatin trials are being run specifically in a jurisdiction structured to sit outside conventional medical regulation

Registry and study records

A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy: PubMed · DOI: 10.1038/mt.2014.200 — n=6, intramuscular AAV1.CMV.FS344, dose-ranging by cohort, 6-minute-walk-test outcome
Follistatin Gene Therapy Improves Ambulation in Becker Muscular Dystrophy: PubMed · DOI: 10.3233/JND-150083 — review of the same trial and follistatin biology
Phase I Clinical Intramuscular Gene Transfer of rAAV1.CMV.huFollistatin344 Trial to Patients With Becker Muscular Dystrophy and Sporadic Inclusion Body Myositis: ClinicalTrials.gov NCT01519349 · n=15, Nationwide Children's Hospital, completed 2017, no results posted on the registry
Phase I/II Clinical Intramuscular Gene Transfer of rAAV1.CMV.huFollistatin344 Trial to Patients With Duchenne Muscular Dystrophy: ClinicalTrials.gov NCT02354781 · n=3, completed 2017, results posted on the registry
A Phase I, Open Label, Single Dose Study to Evaluate the Safety and Efficacy of an Injectable Follistatin Plasmid Gene Therapy in Healthy Subjects: ClinicalTrials.gov NCT06411366 · n=43, Minicircle, completed 2023 in Roatán, Honduras, no results posted
Evaluating the Safety and Efficacy of Injectable Combination Klotho and Follistatin Plasmid Gene Therapy in Humans: ClinicalTrials.gov NCT07285629 · n=14, Minicircle, completed 2026 in Honduras, no results posted
CALM-AF-AI: Counteracting Age-related Loss of Muscle With AAV-Follistatin Combined With Angiogenesis-Inducing VEGF Plasmid Gene Therapy: ClinicalTrials.gov NCT07443826 · n=12 (recruiting), Unlimited Biotechnology LLC, Próspera ZEDE special economic zone, Honduras

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Evidence last reviewed: September 2026. Peptide Proof reports what studies found. We do not give medical advice, dosing guidance, or treatment recommendations.