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Not medical advice. The Atlas is not a substitute for a clinician who can examine you.

Follistatin 344

Myostatin Inhibitor Glycoprotein

Evidence grade 1 of 5, Untested. Read how the Atlas grades evidence.

Follistatin is a real myostatin/activin-binding glycoprotein, and the muscle-growth signal rests almost entirely on animal and in-vitro work. The only completed human muscle data come from a single open-label, uncontrolled Phase 1/2a AAV1.CMV.FS344 gene-therapy study in six Becker muscular dystrophy patients (Mendell et al., 2015), which is proof-of-concept, not a controlled RCT. There is no approved human product, no controlled human muscle-growth RCT, and gray-market FST-344 injectables plus offshore gene-therapy offerings carry no verified human safety RCT, so grade 1 is the honest grade.

FDA
Not approved. No FDA-approved follistatin product for any indication. Gene-therapy use exists only as investigational protocols (open-label Becker MD trial under IND) and as unapproved offshore commercial offerings; gray-market FST-344 is sold as a research chemical not for human consumption.
WADA
Prohibited at all times. Follistatin and myostatin-function modulators fall under WADA hormone/metabolic-modulator provisions, and follistatin gene therapy additionally falls under the gene-doping prohibition.

Reference only. Not medical advice.

What can go wrong

No approved human product and no controlled human muscle RCT; irreversible or excessive hypertrophy and unknown off-target effects are the central concerns, plus contaminated dosing from gray-market vials and elevated LDL reported in offshore recipients.

A naturally produced protein that inhibits myostatin, the body's brake on muscle growth. Dramatically increases muscle mass in animal models; studied in muscular dystrophy.

What people take it for

These are the reasons people give for taking it. They are not effects it has been shown to have.

  • Myostatin inhibition
  • Extreme muscle hypertrophy

How it is supposed to work

Follistatin works by removing a brake. Muscle growth is held in check by myostatin, a protein that tells muscle cells to stop growing; follistatin is a binding protein that traps myostatin (and the related protein activin) before it can reach its receptor, lifting the brake and allowing muscle to grow. It is not a receptor drug but a molecular sponge, and because myostatin is one of the body’s strongest limits on muscle mass, neutralizing it produces, in animals, some of the largest muscle gains seen from any intervention.

Follistatin is a 344-amino-acid glycoprotein, the source of the popular FST-344 name, with other natural isoforms (a membrane-bound FS288 and a circulating FS315) that differ in where they act. The body makes it in the gonads, pituitary and liver, where it regulates the TGF-beta family of signaling proteins. Crucially, it is a large, complex protein, not a small peptide, which matters a great deal for whether an injected version can actually work.

Type
Myostatin/activin trap
Size
344-aa glycoprotein
Human data
Gene therapy only
Injection trials
None
WADA
Prohibited
Approved
No

What Worked Was Gene Therapy, Not The Injection

The gap between follistatin’s biology and the vial sold online is the whole story. The myostatin science is real and dramatic: animals and people with myostatin loss-of-function are spectacularly muscular (the double-muscled Belgian Blue cattle, the so-called mighty mouse), and in rodents and large animals, blocking myostatin with follistatin produces 20 to 40% muscle gains, larger than anabolic steroids in comparable studies. But the marketing erases three decisive facts. First, the human evidence comes almost entirely from gene therapy for muscular dystrophy, with modest and mixed results, not from injecting follistatin protein, which has no published human trial at all. Second, follistatin is a big glycoprotein, so an injected version faces real questions about whether it survives and reaches muscle. Third, the biggest effects appear in diseased or aged tissue with high myostatin, while gains in healthy young muscle can be under 10%. One of the strongest muscle stories in biology is being sold as one of the least proven injectables in the market.

Safety in detail

The muscle-growth reputation is driven by animal data and bodybuilding marketing, not controlled human trials. The only completed human muscle evidence is one small open-label gene-therapy study in six Becker muscular dystrophy patients. The 2015 BioViva/Parrish offshore self-experiment and the ongoing Minicircle offshore commercial gene therapy operate outside FDA oversight and are not peer-reviewed controlled trials, so their outcome claims should be attributed to those companies rather than treated as established.

  • There is no human safety data for injected follistatin protein; the human record is gene therapy, a different intervention.
  • Follistatin suppresses FSH through activin neutralization, so it can affect reproductive hormones and fertility, a real and often-ignored concern.
  • It acts on the broad TGF-beta and activin system involved in many tissues, raising a theoretical cancer concern that systemic, long-term myostatin inhibition has not resolved.
  • Because real recombinant follistatin is difficult and expensive to make, gray-market vials are frequently underdosed, degraded or not genuine follistatin at all.
  • It is prohibited in sport as a myostatin-affecting agent, and follistatin gene therapy is a flagship gene-doping concern.
  • Not approved for any use; gene therapy remains investigational.

Children and teenagers

Follistatin has no place in muscle enhancement for anyone under 18. Manipulating the myostatin and activin system in a developing body is especially inappropriate given its reproductive-hormone effects and broad signaling role. The only pediatric context is follistatin gene therapy for muscular dystrophy, an investigational clinical treatment under specialist care that has nothing to do with gray-market injectable use, which would be unstudied and unsafe in a minor.

What people get wrong

Nothing recorded here yet. There is almost certainly something people get wrong about this one, and the blank space means we have not written it down, not that the record is clean.

Who profits, and who pushes back

Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.

Follistatin sits at the intersection of two very different economies. One is legitimate but investigational: biotech companies developing follistatin gene therapy for muscular dystrophy. The other is the gray market, where peptide vendors sell FST-344 vials and bodybuilding influencers promote it as a muscle holy grail capable of doubling gains. The influencer hype is the engine of demand, and it runs far ahead of any human injection evidence, selling certainty about a product that has never been tested in a human trial.

How we got here

Follistatin was first identified in the 1980s from ovarian fluid as a protein that suppressed follicle-stimulating hormone, hence the name, and was later recognized as a high-affinity binder of activin and then of myostatin (GDF-8), which reframed it as a muscle-growth regulator. The 344-amino-acid isoform (FST-344) became the muscle and gene-therapy workhorse, delivered as AAV1.CMV.FS344 in the Nationwide Children's Hospital Becker muscular dystrophy studies. In 2015 Liz Parrish of BioViva turned it into a widely reported self-experiment, receiving follistatin gene therapy in Colombia outside FDA oversight, a completed and much-criticized episode. It has since been commercialized offshore as a plasmid gene therapy by Minicircle at clinics in the Bahamas, Honduras, and Panama, while separately a gray-market injectable sold as follistatin-344 research chemical circulates in bodybuilding channels with no approved human product behind it.

The story began with myostatin’s discovery in 1997 as the brake on muscle growth, dramatized by the mighty mouse and double-muscled cattle. Follistatin was shown to inhibit myostatin in 2001, and over the 2000s, animal studies produced muscle gains exceeding steroids. That promise drove follistatin gene-therapy programs for muscular dystrophy into Phase 1/2 trials in the 2010s, with modest results. Meanwhile the bodybuilding world adopted injectable FST-344 protein as a muscle peptide, despite the absence of any human injection trial, and influencer marketing turned a complex, unproven biologic into a gym-culture sensation.

  1. 1997Myostatin identified as the negative regulator of muscle mass (the mighty mouse).
  2. 2001Follistatin shown to inhibit myostatin in living animals.
  3. 2000sAnimal studies show 20 to 40% muscle gains via follistatin, exceeding steroids.
  4. 2010sFollistatin gene-therapy trials in muscular dystrophy and myositis report modest, mixed results.
  5. 2010s-2020sInjectable FST-344 protein spreads through bodybuilding, propelled by influencer marketing, with no human injection trials.

The numbers behind the grade

Type
Myostatin inhibitor
Form
344-aa glycoprotein
Human data
Gene therapy only
Injection trials
None
WADA
Prohibited
Approved
No

The people taking it

One of the most hyped muscle-building compounds in bodybuilding, marketed as a genetic-limit-breaking holy grail, and a prime example of marketing running far ahead of human evidence.

Follistatin’s gray-market users are overwhelmingly bodybuilders and strength athletes chasing maximal muscle, plus biohackers drawn to the idea of overriding a genetic limit. A separate, clinical population, patients with muscular dystrophy or muscle-wasting disease, encounters follistatin only through gene-therapy trials. The two could hardly be more different, yet marketing borrows the credibility of the clinical work to sell the injectable to the gym crowd.

Used gray-market by bodybuilders for muscle growth, on the strength of animal and gene-therapy data rather than any human injection trial, and studied legitimately only as gene therapy for muscular dystrophy. Banned in sport.

Set against the alternatives

Follistatin’s comparisons cut against the hype. Against anabolic steroids, its animal effect sizes are larger, but steroids actually work in humans while injected follistatin is unproven in people, so the comparison flatters biology that has not translated. Against pharmaceutical myostatin-inhibitor drugs, the history is sobering: several antibody and receptor-blocking drugs aimed at the exact same pathway, for muscular dystrophy and age-related muscle loss, have failed in clinical trials despite the compelling biology, a direct warning about extrapolating from mice. And against follistatin gene therapy, which is the real human approach under study, the injected protein is the cheaper, unvalidated shortcut. The pattern is consistent: powerful target, disappointing human translation.

What we do not know

  • Whether injected follistatin protein does anything meaningful in humans, given the complete absence of injection trials.
  • Whether it would work in healthy people, where animal gains are far smaller than in diseased tissue.
  • How significant the reproductive and cancer-pathway safety concerns are with sustained use.
  • Why pharmaceutical myostatin-inhibitor drugs have mostly failed despite the same biology.
  • How much gray-market product is even genuine follistatin.

What could change

Gene therapyThe legitimate frontier, with follistatin gene therapy still under study for muscular dystrophy.Myostatin-inhibitor classA broader drug class with a mostly disappointing clinical record that tempers expectations.Injection validationWhether injected follistatin is ever tested in humans remains an open question.Authenticity scrutinyGrowing awareness that much gray-market product may not be genuine follistatin.

The market for this

What follows describes how this is bought and sold. It is not a buying guide and it is not an endorsement of any seller.

There is no approved way to obtain follistatin for muscle growth; it is sold only as research-use-only material, which is not for human use, is banned in sport, and is plagued by authenticity problems. Gene therapy is available only within clinical trials. For anyone tempted, the honest guidance is that the injectable is unproven and the product likely suspect; the muscle gains promised by influencers are not supported by any human trial.

Gray-market vials are priced like other research peptides, but that low cost is itself a warning: genuine recombinant follistatin is expensive and difficult to manufacture, so inexpensive product is likely underdosed, degraded or not real follistatin. The apparent affordability reflects doubtful authenticity more than genuine value.

Almost all gray-market follistatin is synthesized overseas, predominantly in China, and sold as research protein with no quality assurance and a real likelihood that the vial does not contain genuine, active follistatin. An independent certificate of analysis is the minimum check, and even that cannot fully validate a complex glycoprotein.

ChinaThe dominant source of gray-market follistatin protein, sold as research material, with serious questions about whether vials contain genuine, active follistatin.Authenticity problemBecause real recombinant follistatin is hard and costly to produce, cheap vials are a red flag for underdosing, degradation or substitution.Gene-therapy channelThe legitimate human work runs through biotech and clinical trials, an entirely separate and regulated path.

What this entry does not yet cover

What follows is unfinished work on our side, not a finding about Follistatin 344.

Nothing outstanding on this one.

Sources

The studies that matter

  • Lee and McPherron2001

    Demonstrated that follistatin inhibits myostatin in living animals, establishing the mechanism behind its muscle effects.

  • Animal gene-therapy and protein studies2000s-2010s

    Follistatin produced 20 to 40% muscle-mass increases in rodents, sheep and dogs, effect sizes exceeding anabolic steroids, with the largest gains in aged or diseased models.

  • Gene-therapy trials in muscular dystrophy and myositis2010s

    Phase 1/2 follistatin gene-therapy trials in Duchenne/Becker dystrophy and inclusion body myositis reported some functional improvement, with modest and mixed results, the bulk of the human evidence.

  • Injected follistatin protein in humansnone

    No published human trial has tested injected FST-344 for safety or efficacy; the gray-market use rests on animal and gene-therapy data, not on injection studies.