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Follistatin-344

Studied for muscle volume in healthy adults, walking distance in muscle disease and muscle mass in animals. A myostatin- and activin-binding protein. FS344 names the messenger RNA isoform used in gene-therapy trials, while the market sells an injected protein.

categorylongevity
clinical evidenceanimal only
community adoptionniche
uses graded5
sources14
last reviewed24 Aug 2026
compound file

The answer, first. A myostatin- and activin-binding protein. FS344 names the messenger RNA isoform used in gene-therapy trials, while the market sells an injected protein. The strongest evidence is for muscle volume in healthy adults, graded B — one well-powered human trial.

A follistatin-based trap injected into one muscle grew rectus femoris volume 14.5% and tibialis anterior 8.9% in 58 healthy women 6.

Mean strength did not change. The rest of what it is sold for — muscle mass in animals, injected follistatin-344 protein in people, strength or physical function — grade D or E: animal or mechanism data only, or a claim the human trials have already tested and not supported.

What it is used for

Every use graded on its own evidence, not the compound as a whole. 5 outcomes, ranked by what the human record supports.

#outcome · human · animal · gradewhat the best evidence actually shows
01Muscle volume in healthy adultsphase 1, n=58, different molecule · consistentgrade BA follistatin-based trap injected into one muscle grew rectus femoris volume 14.5% and tibialis anterior 8.9% in 58 healthy women 6. Mean strength did not change.
02Walking distance in muscle disease2 open-label trials, n=6 each · supportivegrade CAAV1 carrying the FS344 gene, injected into both quadriceps, improved 6-minute walk by 56 m a year in six myositis patients against matched controls 4. Open-label, gene therapy, n=6. A published critique argues the functional claim is unfounded 13.
03Muscle mass in animalsnot applicable · mice and macaquesgrade DMice engineered to make follistatin in muscle gained mass on the scale of myostatin knockouts 1. Macaque quadriceps grew after gene delivery 2. That primate paper drew an erratum in 2026 3.
04Injected follistatin-344 protein in peopleno trial of any design · local injection onlygrade DNo trial has injected follistatin-344 protein into a person. A doping-control study bought 17 black-market vials. Nine held follistatin, all bacterially His-tagged, and some held MGF or GHRP-2 instead 9. Native follistatin clears too fast to work as an injected protein, which is why every serious programme engineered a longer-lived variant 14.
05Strength or physical function2 randomised trials, n=58 and n=251 · positivegrade ESix months of the same trap grew biceps volume 16.4% against placebo with no consistent functional gain 7. Blocking the same receptor in 251 patients moved 6-minute walk not at all 8.
gradewhat it means
ARegulatory approval, or multiple adequately-powered trials agreeing with each other
BAt least one well-powered human randomised trial, with the direction replicated
CSmall or open-label human trials only
DAnimal or mechanism data only, with no controlled human outcome
EA claim the human trials have already killed

How it works

The proposed mechanism, in three steps. A mechanism is a reason to run a trial, never a substitute for one.

1targetBinds activin A and myostatin in circulation, keeping both off the activin type IIB receptor on muscle 1.
2signalWith myostatin blocked, SMAD2/3 signalling falls and muscle protein synthesis rises. Transgenic mice show the ceiling of that effect 1.
3effectIn people the pathway reliably adds muscle volume. It just as reliably fails to add strength or function 678.

What it does not do

Claims the current record does not support. Worth knowing before you set expectations.

not supported by the evidence

How it is used

What published protocols administered, and what the community reports doing. Descriptive on both counts, and never a recommendation.

routeNo published human route for the protein. Sellers describe subcutaneous or intramuscular injection of reconstituted powder 9.
formatLyophilised recombinant protein in a vial, usually bacterially expressed and His-tagged 9.
published dosesThere are none for the protein. Human studies delivered the FS344 gene by AAV1, at 3 to 6 by 10 to the 11th vector genomes per kilogram per leg 45. The Fc trap ACE-083 was dosed at 50 to 240 mg per muscle every three weeks 67. Neither is what is sold.
human pharmacokineticsNo human pharmacokinetic data for injected follistatin. Native follistatin clears fast enough that developers built Fc fusions instead 11.
reported conventionsAs reported on bodybuilding forums and audited in a doping-control study, 2019: vials are reconstituted and injected subcutaneously or intramuscularly. No peer-reviewed source documents a dose or schedule. Only nine of 17 audited products held follistatin at all 9. Convention, not guidance.
commonly paired withPEG-MGF

This site does not publish protocols to follow. The doses above are what studies administered or what users report, stated as facts about the literature and the market. How protocols are structured, mixing and storage and the reconstitution calculator cover the arithmetic.

What to expect

Where a trial measured it, the trial. Where only the community reports it, that is said out loud.

onsetNo trial has dosed the protein, so nothing about its timing has been measured. In the trap trials muscle volume changed across three to six months of repeated injection 67. Strength never did.
most common reportAs reported: a fuller look in the injected area. No trial has recorded a subjective effect from injected follistatin protein.
adverse effectsFor the protein, no adverse-event data exist. Injection-site reactions were the commonest event with the Fc trap 67. The decoy receptor ACE-031 was halted for nosebleeds and telangiectasia 10. Bimagrumab caused muscle spasms in 51% and diarrhoea in 52% 8.
the stop signalNo stop rule exists for the protein. In the myostatin-pathway trials, bleeding signs and vascular skin changes were what stopped a whole programme 10.

Approval and status

What regulators and sport bodies have actually said, separately from what the evidence shows.

approvalNever approved anywhere, in any form. No follistatin protein product has been registered.
FDANo FDA approval. The gene-therapy trials ran under investigational applications. The injectable protein sold online has never entered one.
sport [WADA]Prohibited at all times. Named in S4.3 as a myostatin-binding protein 12.
sold asresearch chemical

Check the vial

The grade above describes a molecule studied under controlled conditions. It says nothing about the powder in a particular vial.

That gap is the one part of this market a reader can actually close. How to read a certificate of analysis covers the five measures in five minutes, and the 2026 audit grades vendors on the documents they publish against a rubric printed in full.

Questions we get

What is follistatin-344 used for?

It is sold to block myostatin and add muscle. The pathway is real. Mice engineered to make follistatin in muscle gained mass like myostatin knockouts 1. What is not real is the link to the vial.

Every human study used gene delivery or an engineered Fc trap, never the injected protein 46. Grade the outcome and the protein sits on animal data.

How is follistatin-344 used?

There is no published human protocol for the protein, so no dose or schedule has ever been tested 9. Human studies used AAV1 gene delivery into the quadriceps 4.

Others used the Fc trap ACE-083 at 50 to 240 mg per muscle, every three weeks 67. As reported and audited in a 2019 doping-control study, vials are reconstituted and injected subcutaneously or intramuscularly 9. Convention, not guidance.

How long does follistatin-344 take to work?

Nobody has timed the protein, because nobody has trialled it. The nearest evidence is the Fc trap, where muscle volume grew over three to six months of repeated injection into a single muscle 67.

Strength did not follow at any point in either trial. So the honest answer is months for a scan, and never for a lift.

Does blocking myostatin make you stronger?

Nothing published says yes. Two placebo-controlled trials of a follistatin-based trap grew muscle volume 14.5% and 16.4% with no strength or function gain 67.

A 251-patient randomised trial of an anti-activin-receptor antibody showed no difference in 6-minute walk at any dose 8. The scan moves. The muscle does not. That is the single most replicated finding in this whole pathway.

How do I know a vial actually contains follistatin?

For this compound the answer has been measured. Doping-control chemists bought 17 black-market products labelled follistatin. Only nine contained follistatin at all, and some of the rest held MGF or GHRP-2 instead 9.

Every one that did contain it carried a bacterial His-tag, a purification handle absent from human follistatin. Ask for a certificate of analysis for that specific lot, or assume nothing.

References

  1. Lee SJ, McPherron AC. Regulation of myostatin activity and muscle growth. Proc Natl Acad Sci U S A. 2001. PMID 11459935
  2. Kota J, Handy CR, Haidet AM, et al. Follistatin gene delivery enhances muscle growth and strength in nonhuman primates. Sci Transl Med. 2009. PMID 20368179
  3. Erratum for the research article Follistatin gene delivery enhances muscle growth and strength in nonhuman primates. Sci Transl Med. 2026. PMID 42555759
  4. Mendell JR, Sahenk Z, Al-Zaidy S, et al. Follistatin gene therapy for sporadic inclusion body myositis improves functional outcomes. Mol Ther. 2017. PMID 28279643
  5. Mendell JR, Sahenk Z, Malik V, et al. A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy. Mol Ther. 2015. PMID 25322757
  6. Glasser CE, Gartner MR, Wilson D, et al. Locally acting ACE-083 increases muscle volume in healthy volunteers. Muscle Nerve. 2018. PMID 29486514
  7. Statland JM, Campbell C, Desai U, et al. Randomized phase 2 study of ACE-083, a muscle-promoting agent, in facioscapulohumeral muscular dystrophy. Muscle Nerve. 2022. PMID 35428982
  8. Hanna MG, Badrising UA, Benveniste O, et al. Safety and efficacy of intravenous bimagrumab in inclusion body myositis, RESILIENT, a randomised, double-blind, placebo-controlled phase 2b trial. Lancet Neurol. 2019. PMID 31397289
  9. Reichel C, Gmeiner G, Thevis M. Detection of black market follistatin 344. Drug Test Anal. 2019. PMID 31758732
  10. Campbell C, McMillan HJ, Mah JK, et al. Myostatin inhibitor ACE-031 treatment of ambulatory boys with Duchenne muscular dystrophy. Muscle Nerve. 2017. PMID 27462804
  11. Castonguay R, Berasi SP, Zhang Y, et al. Follistatin-288-Fc fusion protein promotes localized growth of skeletal muscle. J Pharmacol Exp Ther. 2019. PMID 30563942
  12. World Anti-Doping Agency. Prohibited List 2026, International Standard, effective 1 January 2026. wada-ama.org
  13. Greenberg SA. Unfounded claims of improved functional outcomes attributed to follistatin gene therapy in inclusion body myositis. Mol Ther. 2017. PMID 28927986
  14. Shen C, Iskenderian A, Lundberg D, et al. Protein engineering on human recombinant follistatin: enhancing pharmacokinetic characteristics for therapeutic application. J Pharmacol Exp Ther. 2018. PMID 29752426

Inside Your Peptides is published by the owners of the next lab, a vendor graded elsewhere on this site. We sell nothing here, and this page carries no vendor link. Grades follow the published criteria in our editorial policy — never referral terms. Research and education only. Not medical advice.