Reviewed & approved by Dr. Nova Reyes · Last checked 2026-10-26. ← Back to Evidence Library

Follistatin (FS344): what the evidence says

Name: Follistatin (FS344)
Creator: Dr. Nova Reyes
Published: 2026-10-26

At a glance

What it is: a natural protein (about 300+ amino acids, not a short peptide) that blocks myostatin and activin, the body's brakes on muscle growth. FS344 is a gene variant that makes the blood-circulating form, FS315. ^R1

What the evidence says: the human data come from gene therapy, where a virus carries the follistatin gene into thigh muscles, not from injecting the protein. In small open-label trials, some people with Becker muscular dystrophy and inclusion body myositis walked farther. ^{R2, R3} Other experts called the myositis claims "unfounded" because there was no proper control group. ^R4 No human study of injected follistatin protein or peptide vials was found.

Biggest risks: follistatin also suppresses FSH, a reproductive hormone. Gene therapy is permanent or long-lasting. Black-market vials often do not contain follistatin. ^{R1, R5}

Rating


Human Human evidence	Limited for AAV gene therapy in muscle disease (6 + 6 patients, open-label) ^{R2, R3} · Very limited, unpublished for offshore plasmid gene therapy registrations ^{R6, R7} · None for injected protein
Animal Animal / lab evidence	Muscle growth and strength in monkeys after gene delivery; mouse disease models ^R8
Regulatory	Never approved · Not on FDA 503A or 503B bulk lists · WADA 2026: prohibited at all times (S4.3, myostatin-binding proteins) ^{R9, R10, R11}
Established human dose	None. Study details lists what trials used

Evidence verdict: Muscle function in muscular dystrophy or inclusion body myositis (gene therapy, not peptide injection): Limited · Muscle gain in healthy people: No controlled data · Injected follistatin peptide: No human data Card verdict: Limited (AAV gene therapy in muscle disease) · Injected follistatin peptide or vials: No human data Card note: Human data is viral gene therapy, not injected peptide vials. Varies by use, see page.

This page reports what studies used. It is not dosing advice.

Legend: HUMAN data · ANIMAL / LAB data · UNKNOWN · UNVERIFIED: not yet confirmed against a primary source

About the evidence: the peer-reviewed gene therapy trials come from Jerry Mendell's group at Nationwide Children's Hospital. ^{R2, R3} Newer "healthy volunteer" registrations come from Minicircle and Unlimited Biotechnology at a Honduras clinic; we found no peer-reviewed results. ^{R6, R7, R12}

What is it?

Follistatin binds myostatin and activin. Animals lacking myostatin grow much more muscle. The gray market sells "follistatin 344" vials as if the protein were a peptide. Related pages: IGF-1 LR3, MGF, MK-677.

Does it work?

Human Becker muscular dystrophy (Mendell 2015): 6 patients got gene therapy into both thigh muscles. Four of six walked 29–125 m farther in 6 minutes; two did not change. No control group. ^{R2, R13}
Human Inclusion body myositis (Mendell 2017): 6 treated patients gained a median 56 m per year on the walk test; 8 untreated comparison patients lost 26 m (p = 0.01). Not randomized, and exercise was part of the protocol. ^R3
Human Critique (Greenberg 2017): argued the myositis results did not support the claimed benefit. ^R4
Human Duchenne: a 3-patient gene therapy trial completed; UNVERIFIED no results found in PubMed. ^R14
Human Offshore gene therapy: Minicircle registered plasmid follistatin studies in healthy adults (43 and 14 enrolled, completed); Unlimited Biotechnology is recruiting for AAV9-follistatin plus VEGF. No peer-reviewed results found. ^{R6, R7, R12}
Animal Monkeys (Kota 2009): gene delivery increased muscle size and strength. ^R8

Is it safe?

Human No adverse effects reported in the 6-patient Becker trial. ^R2
Animal FS344 was chosen to limit effects on the activin and FSH system; other forms affect it more. ^R1
Unknown No safety data for injected protein from vials.
Unknown Long-term gene therapy risks (immune reactions to the virus, lasting effects) in healthy people are unknown.

Gray-market "research use only" follistatin: extra risks

A gray-market vial has no quality control and no guarantee of identity, strength or sterility. We test retail vials blind under the Open Peptide Standard; see /tests/. A passing test covers one batch on one date and does not mean the compound is safe. In a German anti-doping study, only 9 of 17 black-market "follistatin 344" products contained follistatin; some contained other growth peptides such as MGF or GHRP-2 instead. ^R5 A protein this size is very hard to make correctly outside a regulated plant.

What we don't know

Unknown Whether injected follistatin protein does anything in people
Unknown Whether gene therapy helps with proper controls
Unknown Long-term safety of offshore gene therapy

Is it legal?

US (FDA): not approved. Not on the 503A or 503B bulk lists. Gene therapy products need an FDA IND to be given in the US. ^{R9, R10}
Athletes: WADA 2026 S4.3 names follistatin; prohibited at all times. Gene doping is also banned, and detection methods are being developed. ^{R11, R15}

Study details

These are amounts researchers used, not recommendations. | Study | People / model | Route | Amount used | Follow-up | Reported | Citation | |---|---|---|---|---|---|---| | Mendell 2015 (Becker MD) | 6 patients | Gene therapy, injected into thigh muscles | 3 × 10¹¹ or 6 × 10¹¹ vector genomes/kg per leg, once | ~1 year | 4 of 6 walked farther | [PMID 25322757](https://pubmed.ncbi.nlm.nih.gov/25322757/) | | Mendell 2017 (IBM) | 6 treated, 8 comparison | Gene therapy, thigh muscles | 6 × 10¹¹ vector genomes/kg, once | ~1 year | +56 m/year vs −26 m/year | [PMID 28279643](https://pubmed.ncbi.nlm.nih.gov/28279643/) | | Kota 2009 | Monkeys | Gene therapy into muscle | Caution not in abstract | Months | More muscle and strength | [PMID 20368179](https://pubmed.ncbi.nlm.nih.gov/20368179/) |

Full reference list (PubMed, CT.gov, FDA and WADA checked Oct 26, 2026)

^R1 Al-Zaidy SA, et al. J Neuromuscul Dis. 2015. PMID 27858738
^R2 Mendell JR, et al. Mol Ther. 2015. PMID 25322757
^R3 Mendell JR, et al. Mol Ther. 2017. PMID 28279643
^R4 Greenberg SA. Mol Ther. 2017. PMID 28927986
^R5 Reichel C, et al. Drug Test Anal. 2019. PMID 31758732
^R6 ClinicalTrials.gov NCT06411366, phase 1, Minicircle, follistatin plasmid gene therapy in healthy subjects, site in Honduras, completed, 43 enrolled (CT.gov API v2, checked Oct 26, 2026). https://clinicaltrials.gov/study/NCT06411366
^R7 ClinicalTrials.gov NCT07285629, early phase 1, Minicircle, klotho + follistatin plasmid, completed, 14 enrolled (CT.gov API v2, checked Oct 26, 2026). https://clinicaltrials.gov/study/NCT07285629
^R8 Kota J, et al. Sci Transl Med. 2009. PMID 20368179
^R9 FDA, 503A bulk drug substances categories list (updated May 14, 2026). https://www.fda.gov/media/94155/download
^R10 FDA, 503B bulk drug substances categories list (updated Mar 21, 2025). https://www.fda.gov/media/94164/download
^R11 WADA. The 2026 Prohibited List, S4.3. https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf
^R12 ClinicalTrials.gov NCT07443826, phase 1/2, Unlimited Biotechnology LLC, AAV9-follistatin + VEGF plasmid, recruiting, Honduras (CT.gov API v2, checked Oct 26, 2026). https://clinicaltrials.gov/study/NCT07443826
^R13 ClinicalTrials.gov NCT01519349, phase 1, Nationwide Children's Hospital, AAV1 follistatin gene transfer in Becker MD and sporadic IBM, completed, 15 enrolled (CT.gov API v2, checked Oct 26, 2026). https://clinicaltrials.gov/study/NCT01519349
^R14 ClinicalTrials.gov NCT02354781, phase 1/2, AAV1 follistatin gene transfer in Duchenne MD, completed, 3 enrolled (CT.gov API v2, checked Oct 26, 2026). https://clinicaltrials.gov/study/NCT02354781
^R15 Yanazawa K, et al. PeerJ. 2021. PMID 34721976

Disclaimer

This page is for education and harm reduction, not medical advice or a recommendation to use Follistatin (FS344). Talk to a clinician you trust, especially if you are pregnant or trying to conceive (follistatin affects reproductive hormones), have a history of cancer, or are a tested athlete. Report problems to FDA MedWatch (https://www.fda.gov/safety/medwatch).