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Follistatin (FST / FST-344)
A myostatin/activin-binding protein with essentially NO human evidence as an injectable supplement — the real human data are from gene-therapy trials that deliver the follistatin GENE, not the grey-market peptide sold online. Follistatin is a naturally occurring protein that binds and neutralizes myostatin and activin, the molecules that restrain muscle growth. In animals, follistatin (or the follistatin gene) produces dramatic, myostatin-knockout-like muscle hypertrophy, and small open-label gene-therapy trials in Becker muscular dystrophy and inclusion-body myositis reported walking-distance gains. But none of that is the same as injecting recombinant follistatin peptide, which has never been tested in a controlled human supplement trial. It is not an approved drug or a regulated supplement, and the grey-market injectable is unregulated. This entry exists to inform, not to recommend.
Research peptide — not a dietary supplement
Follistatin is a research compound, not a regulated dietary supplement. It is typically administered by injection and sold “for research use only.” The evidence below is largely preclinical (animal and in-vitro) or early-stage, so no evidence score is assigned. This page is provided for transparency and education — it is not a recommendation to use. Consult a qualified healthcare provider, and be aware that purity, dosing, and legal status vary by jurisdiction.
What the evidence says
Most Follistatin studies are mechanism or observational rather than RCTs that measure a clinical effect — keep findings provisional.
Most evidence is from medium-quality randomised trials published 2001–2026 with a typical study size of 62 participants.
Based on 14 studies · 5 RCTs · 365 total participants
Confidence
Moderate confidenceBy outcome
Scored very low because there is no controlled human trial of injectable follistatin; the dramatic results come from animal models and small open-label GENE-therapy studies, a fundamentally different intervention.
3 trials ongoing or recruiting · 10 completed on ClinicalTrials.gov
1 of the completed trials have posted results
Registered trials show research momentum for Follistatin, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Aug 2026
Follistatin (FST; the muscle-relevant isoform is FST-344, alternatively spliced as FS344) is an endogenous glycoprotein that acts as a high-affinity binding protein for activin and myostatin (GDF-8) — the TGF-β-family ligands that signal through the activin type II receptors to hold skeletal-muscle mass in check.
By sequestering those ligands, follistatin removes the brake on muscle growth, which makes it one of the most potent natural myostatin antagonists known. The preclinical case is genuinely striking.
In foundational work (Lee & McPherron 2001), transgenic mice expressing follistatin in muscle developed dramatic hypertrophy comparable to myostatin-knockout animals.
AAV-delivered follistatin gene therapy increased muscle mass and strength in Pompe-disease mice (Foley 2010) and, beyond muscle, reduced obesity-associated metabolic inflammation and protected against post-traumatic osteoarthritis in high-fat-diet mice (Tang 2020).
The most clinically meaningful human data come from gene therapy — and this is the crucial distinction.
In a phase 1/2a open-label trial, the follistatin gene (AAV1.CMV.FS344) injected directly into the quadriceps of six men with Becker muscular dystrophy improved the 6-minute-walk distance in several patients (gains of 29-125 m), with biopsy evidence of muscle hypertrophy and reduced fibrosis and no reported adverse effects (Mendell 2015).
A follow-on open-label trial delivered the same follistatin gene to the quadriceps of six patients with sporadic inclusion-body myositis and reported a +56 m/year walking improvement versus a decline in untreated controls (Mendell 2017).
These are encouraging, but they are small, unblinded, single-centre studies of localized GENE delivery — a fundamentally different intervention from injecting recombinant follistatin protein subcutaneously, which is what the grey-market 'follistatin peptide' actually is.
Here is the load-bearing caveat: there is no controlled human trial of injectable recombinant follistatin as a supplement. None.
The dramatic results belong to animal models and to gene therapy delivered under research protocols; the systemic safety, pharmacokinetics, and efficacy of self-injected follistatin protein in healthy humans are completely uncharacterized.
Follistatin also has broad biology beyond muscle — it regulates reproductive hormones (FSH), inflammation, and tissue repair — so chronically raising it could have effects that have never been studied in this context.
It is not an approved drug and not a lawful dietary-supplement ingredient; material sold online is an unregulated grey-market product with no guarantee of identity, purity, sterility, or dose.
The evidence here is therefore scored very low — an impressive animal-and-gene-therapy story with zero controlled evidence for the peptide people actually buy — and sandboxed out of all goal- and stack-based recommendations.
Follistatin is a natural high-affinity binding protein for activin and myostatin (GDF-8) — the TGF-β-family ligands that signal through activin type II receptors to limit muscle mass. By sequestering them, follistatin blocks that inhibitory signal. Demonstrated biochemically and in animals; not characterized for injected recombinant follistatin in humans.
With myostatin/activin neutralized, the brake on muscle growth is released. In transgenic and AAV-follistatin mice this produces dramatic, myostatin-knockout-like hypertrophy with larger fibres and greater strength. Established in animals; in humans this effect has only been seen with localized follistatin GENE therapy, not injected protein.
Because follistatin binds activin, it also influences reproductive hormone signalling (FSH), inflammation, and tissue repair. Animal work shows it can reduce metabolic inflammation and protect joints — but this broad biology means chronically raising follistatin could have effects far beyond muscle, none of which are studied for the injected peptide in humans.
How Follistatin works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
Avoid — there is no controlled human trial of injectable follistatin, no approved use, and no quality-controlled product. The animal and gene-therapy evidence does not justify self-injection of the peptide.
Avoid — follistatin affects activin/FSH signalling and interactions are unstudied and unpredictable.
Avoid entirely — completely unstudied, and follistatin influences reproductive-hormone biology.
Follistatin binds activin and thereby influences FSH and reproductive-hormone signalling. Self-injecting it alongside fertility or hormone treatments is theoretically able to perturb that axis and has never been studied in humans.
There are no controlled human drug-interaction data for injectable follistatin. Its broad activin/TGF-β biology (muscle, hormones, inflammation, tissue repair) means interactions cannot be predicted.
Tip: Injectable recombinant follistatin has never been studied as a supplement in a controlled human trial — the side-effect profile in people is genuinely unknown. This is itself the warning.
Tip: Follistatin's broad activin/TGF-β biology means chronically raising it could affect FSH and other systems; long-term human consequences are unstudied.
Tip: Grey-market injectable material has no identity/purity/sterility guarantees; contaminants and injection-related infection are possible.
The current evidence for Follistatin is insufficient to assign an evidence score, based on 9 indexed studies. A myostatin/activin-binding protein with essentially NO human evidence as an injectable supplement — the real human data are from gene-therapy trials that deliver the follistatin GENE, not the grey-market peptide sold online. Follistatin is a naturally occurring protein that binds and neutralizes myostatin and activin, the molecules that restrain muscle growth. In animals, follistatin (or the follistatin gene) produces dramatic, myostatin-knockout-like muscle hypertrophy, and small open-label gene-therapy trials in Becker muscular dystrophy and inclusion-body myositis reported walking-distance gains. But none of that is the same as injecting recombinant follistatin peptide, which has never been tested in a controlled human supplement trial. It is not an approved drug or a regulated supplement, and the grey-market injectable is unregulated. This entry exists to inform, not to recommend. Representative study: PMID 11459935.
The commonly studied dose of Follistatin is No legitimate or recommended dose — follistatin is not an approved medicine or a regulated supplement, and there is no controlled human dosing data for injectable recombinant follistatin. We do NOT provide a dosing protocol. The human evidence comes from localized follistatin GENE therapy delivered under research protocols (intramuscular AAV), which has no bearing on a dose for self-injected peptide.. Individual needs vary — start at the lower end of the range and adjust based on how you respond.
Timing is flexible for Follistatin — consistent daily use matters more than the time of day. There is no validated human dosing schedule for injectable follistatin because it has never been tested as a supplement in a controlled trial.
Follistatin should be used with caution — talk to a healthcare provider before taking it. The most commonly reported side effects are unknown human side-effect profile (injectable peptide), unknown effects on reproductive hormones, inflammation and tissue repair, harm from an unregulated, impure or non-sterile product. Use caution if any of these apply to you: Not an approved medicine and not a regulated dietary supplement — unapproved grey-market injectable; do not self-source; No controlled human safety data exists for injectable recombinant follistatin; Pregnancy and breastfeeding (entirely unstudied; follistatin affects reproductive-hormone/FSH signalling).
Mecasermin (IGF-1)
Mostly mechanism / observationalThe pharmaceutical-grade version of IGF-1 — an FDA/EMA-approved prescription injectable, but approved ONLY for a rare childhood growth disorder (severe primary IGF-1 deficiency / Laron syndrome), where it genuinely raises height velocity in clinical trials. It is the regulated counterpart to the grey-market igf-1-lr3 peptide bodybuilders inject, and shares the same core risks. Crucially, there is NO trial supporting its off-label use for muscle, performance, or anti-aging in healthy adults — and IGF-1's documented harms (hypoglycemia, intracranial hypertension, lymphoid/tonsillar hypertrophy, and a theoretical cancer concern because IGF-1 is mitogenic) are real. Not a dietary supplement, not a longevity drug.
Insulin (bodybuilding use)
Mostly mechanism / observationalInsulin is a life-saving prescription hormone for diabetes — and, used illicitly by bodybuilders as an off-label 'anabolic,' one of the most dangerous performance drugs in existence. The theory is nutrient partitioning: insulin drives glucose and amino acids into muscle and suppresses muscle-protein breakdown. But there is NO controlled evidence that insulin builds muscle or improves performance in healthy, non-diabetic athletes — and a non-diabetic who injects it risks profound, sometimes FATAL hypoglycemia (coma, seizures, brain injury, death), plus fat gain. This is a harm-reduction reference documenting a popular, deadly misuse, NOT a recommendation and NOT a dietary supplement.
ACE-031
Mostly mechanism / observationalAn investigational myostatin/activin 'trap' whose only human trial in patients was STOPPED for safety. ACE-031 is a fusion protein of the activin receptor type IIB (ActRIIB) extracellular domain and an IgG1-Fc, engineered by Acceleron Pharma to soak up myostatin and related ligands and thereby release the brake on muscle growth. It has real human data — a single-dose study in healthy postmenopausal women showed a genuine ~3% gain in lean mass — but its phase 2 trial in boys with Duchenne muscular dystrophy was HALTED after the second dosing regimen because of bleeding-related safety signals (nosebleeds/epistaxis and telangiectasias, dilated surface blood vessels). It is NOT an approved drug, development was discontinued, and anything sold grey-market under this name is unregulated. This entry exists to inform, not to recommend.
CJC-1295
Mostly mechanism / observationalA synthetic long-acting analog of growth-hormone-releasing hormone (GHRH), promoted online to raise GH and IGF-1 for muscle, fat loss and 'anti-aging'. Honest appraisal: the only real human data are two small early-phase pharmacokinetic / safety studies from ~2006 that showed it raises GH and IGF-1 for days — they were never followed by efficacy trials in muscle, body composition or aging. There are NO human outcome RCTs. It is not a dietary supplement: it is sold 'for research use only', is injectable, and is banned by WADA. The original DAC version's clinical development was abandoned.
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Reviewed by Dr. Baher Al Hakim · Last reviewed June 2026 · evidence from 14 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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