A study published in 2019 tested 17 black-market products labeled follistatin 344. Nine contained follistatin. Some of the rest held other growth-promoting peptides, including MGF and GHRP-2.
A follistatin-based drug injected into patients’ muscles made the muscle bigger in two randomized trials. Strength and function gains were limited and inconsistent.
This page covers what follistatin is, what the mouse and human studies found, what the counterfeit study showed, and where follistatin stands with anti-doping rules.
Quick takeaways
| Topic | What the sources say |
|---|---|
| What it is | Large secreted protein that binds myostatin and activins. FS344 is processed into FS315 (1, 2) |
| Mouse data | Transgenic mice making follistatin in muscle gained muscle mass comparable to myostatin knockouts (1) |
| Human data | Two small gene therapy trials (6 patients each) and two randomized trials of a follistatin-based drug, ACE-083 (3, 4, 5, 11) |
| Weak point | ACE-083 raised muscle volume without consistent functional gains (5) |
| Counterfeits | 9 of 17 black-market “follistatin 344” products contained follistatin (6) |
| WADA | S4, prohibited at all times (7) |
What follistatin is
Follistatin is a secreted protein that binds myostatin and activins. Myostatin holds back muscle growth, and follistatin blocks it from reaching its receptor in cell experiments (1).
The “344” in the name comes from a splice variant of the gene. After translation, FS344 is processed into FS315, the form that circulates in blood. FS315 binds activin about 10 times less tightly than another variant, FS288 (2). Sellers label most products 344 and a few 315 (6).
It’s a full-size protein, far larger than the short peptides sold beside it.
What the mouse study found
In 2001, Lee and McPherron made transgenic mice that produced follistatin in skeletal muscle. Their muscle mass rose dramatically, comparable to mice with the myostatin gene knocked out (1).
Those mice made follistatin in their muscle from early development. Nobody injected a protein.
What human studies found
Most human studies of follistatin-based treatments were in patients with muscle disease, and a first-in-human ACE-083 study enrolled healthy women (12). None tested injected follistatin 344 protein.
| Study | People | What was given | Result |
|---|---|---|---|
| Becker muscular dystrophy, 2015 (3) | 6 adults | AAV1 gene carrying FS344, injected into both quadriceps | 6-minute walk changed +58, +125 and 0 m (lower dose) and +108, +29 and 0 m (higher dose) |
| Sporadic inclusion body myositis, 2017 (4) | 6 treated, 8 matched untreated | Same type of gene therapy, both quadriceps | +56.0 m per year vs -25.8 m per year (p=0.01) |
| Facioscapulohumeral dystrophy, 2022 (5) | 58 | ACE-083 or placebo (randomized), injected into the biceps or the tibialis anterior (shin) muscle | Muscle volume +16.4% (biceps) and +9.5% (shin) vs placebo. No consistent functional improvement |
| Charcot-Marie-Tooth disease, 2022 (11) | 45 in the randomized part | ACE-083 or placebo (randomized), injected into the tibialis anterior (shin) muscle | Muscle volume +13.5% vs placebo and better ankle dorsiflexion strength. All other functional outcomes were not significantly better |
The two gene therapy trials delivered a virus carrying the FS344 gene, so the muscle made follistatin itself. Both were open-label. The Becker trial reported no adverse effects in six patients (3). The inclusion body myositis comparison group was eight matched untreated patients (4).
ACE-083 is a follistatin-based fusion protein designed to act on the muscle it’s injected into (8). In the FSHD trial, muscle volume rose, but there were no consistent improvements in function or patient-reported outcomes (5). In the Charcot-Marie-Tooth trial, muscle volume rose and ankle dorsiflexion strength improved, but the other functional outcomes didn’t (11). The registry lists three ACE-083 phase 2 studies as terminated (9).
Safety
A 2015 review says follistatin interacts with the pituitary activin-inhibin axis and can suppress follicle-stimulating hormone, which called for caution in clinical use. The FS344 variant was chosen to get around that (2). Anyone concerned about fertility should raise that with a clinician.
In the FSHD trial, the most common adverse events were mild or moderate injection-site reactions. During the double-blind period, 11 of 28 ACE-083 recipients (39.3%) and 1 placebo participant (3.3%) developed anti-ACE-083 antibodies (5).
What the counterfeit study found
Reichel and colleagues, working at the Seibersdorf doping control laboratory in Austria and the German Sport University Cologne, tested 17 products labeled follistatin 344. Only nine contained follistatin. Some of the others held MGF or GHRP-2 (6).
All nine products that contained follistatin carried a His-tag and contained many oligomers. A His-tag is a purification tag the body’s own follistatin doesn’t have, so it lets a lab tell the two apart (6).
It’s a snapshot of 17 products, published in 2019. It shows why a label isn’t proof of what’s inside.
Follistatin isn’t Follistim
The names look alike. Follistim AQ is follitropin beta, a recombinant follicle-stimulating hormone approved for ovulation induction, IVF cycles and sperm production in men with hypogonadotropic hypogonadism (10). It’s a different molecule.
Anti-doping status
The 2026 WADA Prohibited List names “myostatin-binding proteins (e.g. follistatin, myostatin propeptide)” under S4. S4 is prohibited at all times, in and out of competition (7). The 2019 counterfeit paper noted that no approved pharmaceutical formulations of follistatin were available (6).
How to judge a listing
A “research use only” label is the seller’s wording and carries no approval. A certificate of analysis describes one lot, and for a protein it has to show identity as well as purity. Look for these:
- Identity test. Mass spectrometry or an immunoblot that confirms follistatin, not only a purity percentage.
- Isoform. The report and label say 344 or 315, and say whether the protein carries a His-tag.
- Batch number. It matches the number on the vial.
- Independent lab. Not the seller’s own, with a name, date and method you can look up.
- Verification. The lab lets you confirm the report on its own site.
Red flags are promised muscle gains, testimonials about physical results, and injection instructions on the product page.
Seller comparison
See how sellers compare on lab reports
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Frequently asked questions
What is follistatin 344?
FS344 is a splice variant of follistatin, a secreted protein that binds myostatin and activins. After translation it is processed into FS315, the form found in blood.
Does follistatin 344 build muscle in humans?
No study has shown it. Two small gene therapy trials of FS344 reported walking-distance gains in patients with muscle disease, and a randomized trial of the follistatin-based drug ACE-083 raised muscle volume without consistent functional gains. None tested injected follistatin 344 protein.
Is follistatin 344 the same as follistatin 315?
They are linked. FS344 is processed after translation into FS315. Sellers label most products 344 and a few 315.
Is follistatin banned in sport?
Yes. WADA’s 2026 list names follistatin under S4, which is prohibited at all times.
How many black-market follistatin products were real?
In a 2019 study, nine of 17 products labeled follistatin 344 contained follistatin. Others held MGF or GHRP-2.
Is follistatin the same as Follistim?
No. Follistim AQ is follitropin beta, a recombinant follicle-stimulating hormone approved for fertility treatment.
This page is information, not medical advice. No follistatin drug is approved for human use. Talk to a clinician before using any unapproved compound.
References
- Lee SJ, McPherron AC. Regulation of myostatin activity and muscle growth. Proc Natl Acad Sci USA. 2001;98(16):9306-9311. PMID 11459935.
- 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. A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy. Mol Ther. 2015;23(1):192-201. PMID 25322757.
- Mendell JR, et al. Follistatin gene therapy for sporadic inclusion body myositis improves functional outcomes. Mol Ther. 2017;25(4):870-879. PMID 28279643.
- Statland JM, et al. Randomized phase 2 study of ACE-083, a muscle-promoting agent, in facioscapulohumeral muscular dystrophy. Muscle Nerve. 2022;66(1):50-62. PMID 35428982.
- Reichel C, Gmeiner G, Thevis M. Detection of black market follistatin 344. Drug Test Anal. 2019;11(11-12):1675-1697. PMID 31758732.
- World Anti-Doping Agency. The 2026 Prohibited List, section S4.
- Pearsall RS, et al. Follistatin-based ligand trap ACE-083 induces localized hypertrophy of skeletal muscle with functional improvement in models of neuromuscular disease. Sci Rep. 2019;9:11392. PMID 31388039.
- ClinicalTrials.gov: NCT02927080, NCT03124459 and NCT03943290 (ACE-083 phase 2 studies).
- Organon. Follistim AQ Cartridge prescribing information.
- Thomas FP, et al. Randomized phase 2 study of ACE-083 in patients with Charcot-Marie-Tooth disease. Neurology. 2022;98(23):e2356-e2367. PMID 35545446.
- Glasser CE, et al. Locally acting ACE-083 increases muscle volume in healthy volunteers. Muscle Nerve. 2018;57(6):921-926. PMID 29486514.