Follistatin: A Myostatin-Inhibiting Glycoprotein for Muscle Hypertrophy Research

This content is provided by Superpower Health for educational and informational purposes only. Superpower Health does not prescribe, sell, or facilitate access to follistatin in any form. Follistatin is not FDA-approved for human use as an injectable compound or gene therapy outside of registered clinical trials. This page is not a substitute for medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider.

The idea of removing the body's built-in brake on muscle growth has circulated in exercise science for decades. Cattle with natural myostatin gene mutations develop skeletal muscles so pronounced that their anatomy looks altered. A child born with a loss-of-function myostatin mutation developed measurable muscle hypertrophy from infancy. These observations created intense interest in blocking the myostatin pathway — and in follistatin, the endogenous protein that does exactly that. What the research actually shows, however, differs substantially from what circulates on bodybuilding forums and gray-market peptide vendor sites.

This article covers what follistatin is, how it interacts with myostatin and activin, what the animal and clinical gene-therapy data show, where the evidence stops, and what "follistatin peptide" sold online actually represents.

Key Takeaways

• Regulatory Status: As of April 2026, no injectable follistatin product is FDA-approved for any indication. Follistatin gene therapy (AAV1-FS344) has been investigated in Phase 1/2a clinical trials at Nationwide Children's Hospital for Becker muscular dystrophy and sporadic inclusion body myositis; it is not commercially available. Injectable "follistatin peptide" sold online has no approved regulatory pathway in the United States.
• Research Stage: Extensive preclinical data in rodents and nonhuman primates; limited Phase 1/2a human gene-therapy data in specific neuromuscular disease populations; no human efficacy data for injectable follistatin fragments.
• Availability: Not available through Superpower. "Follistatin 344" or "FST-315" products sold through research chemical vendors are not regulated by the FDA, have not been evaluated for purity or safety in humans, and have no established injectable pharmacokinetics in humans.
• Compound reference: PubChem CID 378611 — Follistatin
• What it is: An endogenous glycoprotein that binds and neutralizes myostatin, activin, and several bone morphogenetic proteins, suppressing their downstream signaling.
• What the research shows: Animal models demonstrate dramatic muscle hypertrophy via myostatin and activin inhibition; a Phase 1/2a gene-therapy trial in Becker muscular dystrophy patients showed functional improvement in a small cohort; no completed human efficacy data exists for injected follistatin fragments as of April 2026.

What Follistatin Is and Where It Comes From

Discovery and identity

Follistatin was identified as an activin-binding protein in a 1990 paper in Science by Nakamura, Takio, Eto, Shibai, Titani, and Sugino, who purified the binding protein from rat ovary and showed it was identical to follistatin, a specific inhibitor of pituitary follicle-stimulating hormone (FSH) release. The name derived from this FSH-suppressing function, observed in the context of reproductive physiology. The protein is encoded by the FST gene and is produced by a range of tissues including the liver, ovary, skeletal muscle, and pituitary. It is a glycoprotein, meaning it carries sugar chains that affect its stability, tissue distribution, and binding properties.

Follistatin belongs to a family of proteins that act as extracellular inhibitors of TGF-beta superfamily ligands. It works by binding directly to its target ligands — primarily activin and myostatin — and sterically blocking them from engaging their cell-surface receptors. Unlike a receptor antagonist that competes at the binding site, follistatin sequesters the ligand itself before receptor contact occurs.

Isoforms: FS-288 and FS-315

Follistatin exists in at least two major isoforms generated by alternative mRNA splicing: FS-288 (follistatin-288) and FS-315 (follistatin-315), with the numbers referring to the amino acid count of the mature protein. These isoforms differ meaningfully in their biology. Schneyer and colleagues reported in a 2004 paper in the Journal of Clinical Endocrinology and Metabolism that FS-288 binds heparan sulfate proteoglycans on cell surfaces and in the extracellular matrix, keeping it locally tethered, while FS-315 circulates freely in the bloodstream and represents the predominant form measured in serum. Sidis and colleagues, publishing in Endocrinology in 2006, characterized the differential binding specificities of these isoforms and showed that FS-288 and FS-315 differ in their relative affinities for activin, myostatin, and bone morphogenetic proteins (BMPs), with functional consequences for where each isoform acts in tissue.

"Follistatin 344" referenced in gray-market peptide markets is typically described as a truncated or recombinant fragment, though the biological identity and manufacturing quality of products sold through unregulated channels is unknown and unverified.

The Myostatin Pathway: Why Follistatin Matters for Muscle

Myostatin as a negative regulator of muscle mass

The foundational work establishing myostatin as a brake on muscle growth came from a 1997 paper in Nature by McPherron, Lawler, and Lee. Mice in which the myostatin gene (GDF-8) was knocked out showed approximately two to three times greater skeletal muscle mass than normal controls, demonstrating that myostatin is a potent negative regulator of muscle development. The same research group subsequently identified that the double-muscled phenotype in Belgian Blue and Piedmontese cattle — reported by McPherron and Lee in PNAS in 1997 and characterized in parallel by Grobet and colleagues in Nature Genetics that same year and by Kambadur and colleagues in Genome Research — was caused by loss-of-function mutations in the bovine myostatin gene. This multi-study convergence established the myostatin–muscle mass axis as a robust biological phenomenon, not an artifact of a single model.

Human evidence followed from a landmark 2004 case report in the New England Journal of Medicine by Schuelke and colleagues, describing a child with a loss-of-function mutation in the myostatin gene who demonstrated unusual muscle bulk from early infancy without obvious pathology. This was the first confirmed human case of myostatin pathway disruption producing gross muscle hypertrophy, providing direct proof of concept that the myostatin axis regulates muscle mass in people.

How follistatin intersects with myostatin and activin

Myostatin signals through two cell-surface receptors, ACVR2A and ACVR2B, which it shares with activin A and several other TGF-beta ligands. Activin acts through the same receptors and also suppresses muscle growth, though through overlapping but distinct downstream mechanisms. Follistatin binds both myostatin and activin with high affinity, neutralizing their ability to engage these receptors. This dual inhibition is critical to understanding the preclinical muscle data.

A 2007 study in PLoS ONE by Lee demonstrated that transgenic mice expressing follistatin in skeletal muscle (F66 line) on a myostatin-null background (F66/Mstn−/−) showed approximately four-fold greater muscle mass than wild-type controls, substantially exceeding the roughly two- to three-fold hypertrophy seen with myostatin knockout alone — evidence that follistatin blocks a second TGF-beta ligand (activin) beyond myostatin. Per-group sample sizes and p-values were not reported in the abstract. Gilson and colleagues, publishing in the American Journal of Physiology — Endocrinology and Metabolism in 2009, characterized the cellular mechanism, showing that follistatin-induced muscle hypertrophy in mice involved both satellite cell proliferation and simultaneous inhibition of myostatin and activin signaling. The synergistic effect of blocking two inhibitory ligands at once explains why follistatin-based approaches have attracted more research interest than selective myostatin inhibitors alone.

Large-animal and transgenic models

Beyond rodents, Chang, Fang, and colleagues reported in Transgenic Research in 2017 that transgenic pigs expressing human follistatin-344 showed increased skeletal muscle mass (relative muscle weight ~11% greater than wild-type controls) without gross pathological findings, extending the model from rodents to a larger mammal with anatomy more similar to humans. Iyer, Chugh, and colleagues, publishing in Neurobiology of Aging in 2021, demonstrated in 24–27-month-old mice that AAV-delivered follistatin overexpression produced skeletal muscle hypertrophy and torque gains alongside improved neuromuscular junction innervation and transmission fidelity (reduced jitter and blocking frequency on single-fiber electromyography) — connecting the hypertrophy effect to a functional outcome relevant to sarcopenia biology. Han, Møller, and colleagues, writing in the Journal of Cachexia, Sarcopenia and Muscle in 2019, reported that follistatin-288 muscle overexpression in mice (rAAV6:Fst288 intramuscular delivery, n = 6–8 per group) increased insulin-stimulated glucose uptake by approximately 75% in lean animals (p < 0.05) two weeks after administration, completely normalized impaired glucose uptake in diet-induced obese insulin-resistant mice, and was accompanied by increased phosphorylation of AKT, TBC1D4, PAK1, pyruvate dehydrogenase-E1α, and p70S6K — describing a metabolic consequence beyond mass gain alone.

Follistatin Gene Therapy: What the Human Data Shows

The AAV1-FS344 program at Nationwide Children's Hospital

The most substantial human evidence for follistatin's biological activity comes not from injected protein but from gene therapy trials using adeno-associated viral (AAV) vectors to deliver the FS344 sequence directly to muscle tissue. The research program at Nationwide Children's Hospital in Columbus, Ohio, led by Jerry Mendell, represents the primary published human clinical dataset. AAV1-FS344 delivers the follistatin gene using an adeno-associated viral vector injected directly into specific muscle groups, allowing local protein expression at the injection site over time. This is mechanistically distinct from injectable follistatin peptide fragments: the gene therapy produces sustained local follistatin protein from the muscle itself, while an injected peptide would require repeated dosing and has undefined pharmacokinetics in humans.

Becker muscular dystrophy trials

Mendell and colleagues published Phase 1/2a trial results for Becker muscular dystrophy (BMD) in Molecular Therapy in 2015. Six ambulatory BMD patients received bilateral intramuscular injections of AAV1-FS344 into the quadriceps across two dose cohorts (3 × 10^11 vg/kg/leg in three patients; 6 × 10^11 vg/kg/leg in three patients). At 180 days, four of six patients showed improvement on the six-minute walk test (individual gains of 58 m, 125 m, 108 m, and 29 m), with histological analysis showing reduced fibrosis, decreased central nucleation, and improved fiber size distribution in treated muscles. No adverse effects were reported during the trial period, though no placebo control and no p-values for the primary functional outcome were provided. A follow-up report in the Journal of Neuromuscular Diseases from the same group provided additional ambulatory function data from the same cohort. This was a small, uncontrolled Phase 1/2a study with no placebo comparison and a primary safety objective; the functional signals are notable but cannot establish efficacy in the statistical sense that a controlled trial would require.

Sporadic inclusion body myositis

A separate Phase 1/2a study by Mendell and colleagues in Molecular Therapy in 2017 examined AAV1-FS344 for sporadic inclusion body myositis (sIBM), an inflammatory muscle disease affecting primarily older adults that has no approved pharmacological treatment. Six sIBM patients received bilateral intramuscular quadriceps injections of rAAV1.CMV.huFS344 at 6 × 10^11 vg/kg and were compared with eight matched untreated controls over one year. The treated group gained +56.0 m on six-minute walk distance vs. a −25.8 m decline in untreated controls (p = 0.01), with individual treated responses ranging 5–153 m and histopathology showing decreased fibrosis and improved regeneration. As with the BMD study, this was a small, uncontrolled, open-label cohort; the results are hypothesis-generating rather than definitive. Mariot and colleagues, publishing in Nature Communications in 2017, raised a broader concern relevant to myostatin-pathway therapies in human neuromuscular diseases: their data suggested that the myostatin pathway is often already downregulated in affected muscle tissue, which may explain why myostatin-pathway interventions have shown modest effects in multiple human trials.

Additional preclinical gene-therapy data

Outside of BMD and sIBM, Giesige and colleagues reported in JCI Insight in 2018 that AAV-mediated follistatin gene therapy improved functional outcomes in the TIC-DUX4 mouse model of facioscapulohumeral muscular dystrophy (FSHD), extending the gene-therapy approach to a third neuromuscular disease context in preclinical work.

Nonhuman primate safety and efficacy data

Before the human trials, Kota and colleagues published critical nonhuman primate data in Science Translational Medicine in 2009. Intramuscular injection of AAV1-FS344 (total 1 × 10^13 vector genomes in 1.5 mL via three right-quadriceps injections; n = 3 cynomolgus macaques per promoter group) produced an approximately 15% increase in muscle mass over baseline at 8 weeks with the CMV promoter (10% with MCK), sustained transgene expression out to 15 months, and no abnormal morphology or function in cardiac or other key organs. Rodino-Klapac and colleagues, publishing in Muscle and Nerve in 2009, reviewed the preclinical and mechanistic rationale for follistatin-based approaches to neuromuscular disease based substantially on this nonhuman primate dataset. Together, these publications provided the safety and efficacy evidence supporting the human dose escalation.

Regulatory and Legal Status

FDA classification and injectable products

As of April 2026, no follistatin product is FDA-approved for any human therapeutic indication. Follistatin gene therapy is in investigational stages only, available through registered clinical trials at specific institutions. It is not approved, commercially available, or accessible through compounding pharmacies.

Injectable "follistatin peptide" products sold through online research chemical vendors — typically described as "follistatin 344" or "FST-315" — occupy an entirely different regulatory and scientific category. These are not gene therapy products. They are described as recombinant protein fragments or synthetic peptide analogs, but the actual identity, purity, and manufacturing conditions of products sold through unregulated channels are unknown. There is no FDA-approved injectable follistatin product, no established pharmacokinetics for injected follistatin fragments in humans, and no clinical trial evidence supporting the use of such products.

WADA and sport ban status

For athletes, follistatin presents a distinct regulatory concern. A 2023 paper in Drug Testing and Analysis by Walpurgis, Agricola, and colleagues characterized myostatin-inhibitory peptides relevant to sports drug testing, describing mass-spectrometric approaches for detecting this compound class — the authors noted that proactive detection-assay development is essential because these peptides are readily available on the research and black markets. Yanazawa, Sugasawa, and colleagues in a 2021 PeerJ paper, developed a gene-doping detection method (TaqMan-qPCR against an rAdV human-follistatin transgene) that identified circulating transgene fragments for several days after injection in mice. Wong, Cheung, and colleagues, writing in Drug Testing and Analysis in 2024, reported the first screening and confirmation method for recombinant human follistatin in equine plasma, combining ELISA screening with mass-spectrometric confirmation for horseracing doping control. As of the 2026 WADA Prohibited List, follistatin and myostatin-pathway inhibitors fall under the S4 (hormone and metabolic modulators) category and the gene-doping prohibition. Athletes subject to anti-doping testing should consult their governing body or a qualified anti-doping advisor before any exposure.

What this means in practice

Products labeled as "follistatin 344" or similar sold through online vendors are not regulated by the FDA. Independent peptide testing programs have identified contamination, incorrect peptide identity, and dosing inconsistency across research chemical products in this class. There is no legal pathway to obtain pharmaceutical-grade injectable follistatin for human use outside of a registered clinical trial. The full-length follistatin protein as a gene therapy target remains an investigational compound with restricted access even within clinical settings.

Safety: What Is and Is Not Known

Absence of clinical safety data for injectable follistatin

No Phase 1 human safety data has been published for injectable follistatin protein or peptide fragments. The clinical trial safety information that exists is specific to intramuscular gene therapy (AAV1-FS344), a route of administration and mechanism entirely different from subcutaneous or intravenous injection of peptide fragments. Extrapolating the gene-therapy safety profile to injected follistatin peptides is not scientifically supported; the pharmacokinetics, tissue distribution, receptor exposure patterns, and off-target effects differ between modalities.

Cardiac signal: myostatin has a role in cardiac function

A substantive safety signal in the preclinical literature concerns cardiac biology. Biesemann and colleagues, publishing in Circulation Research in 2014, demonstrated that myostatin regulates cardiac energy homeostasis and that disruption of myostatin signaling in the heart can impair cardiac function in mouse models. Knapp, Supruniuk, and Górski reviewed the myostatin-cardiac axis more comprehensively in a 2023 paper in Biomolecules, synthesizing evidence that myostatin is involved in the development of cardiac cachexia and cardiac fibrosis in chronic heart failure — raising the possibility that systemic myostatin blockade could have unanticipated cardiovascular consequences. Because follistatin inhibits myostatin systemically (not only in skeletal muscle), sustained follistatin activity could theoretically affect cardiac myostatin signaling. This concern has not been tested in the context of injected follistatin fragments and represents an uncharacterized risk.

Oncology concern: follistatin in cancer biology

A separate concern arises from cancer biology. Cole, Panesso-Gómez, and colleagues reported in Clinical Cancer Research in 2023 that quiescent ovarian cancer cells secrete follistatin as a mechanism to induce chemotherapy resistance in surrounding cells, with antibody or genetic blockade of follistatin sensitizing tumor cells to chemotherapy and elevated tumor follistatin expression correlating with worse patient survival. Elevated follistatin has also been implicated in the biology of other tumor types through its suppression of activin, which normally has antiproliferative activity in certain tissue contexts. Because activin functions as a growth suppressor in several cancer lineages, chronic follistatin-driven activin inhibition raises a theoretical concern about tumor promotion or chemotherapy resistance in individuals with occult malignancy. This risk has not been characterized in humans using exogenous follistatin.

Risks from unregulated sources

Products sold through online research chemical vendors labeled as follistatin are manufactured without regulatory oversight, without GMP standards, and without third-party verification of identity or purity. Serum myokine biomarker research, including a 2024 paper in Biology of Sport by Donati, Biasini, and colleagues that profiled ten candidate myokine biomarkers of myostatin inhibition in elite athletes and identified musclin, follistatin-like 1, and oncostatin as most closely correlated with myostatin, has highlighted the analytical complexity of detecting and quantifying myostatin-pathway activity in biological samples — underscoring the difficulty of even confirming whether an unregulated product contains what it claims to contain.

Who Should Not Use Follistatin

Based on the compound's proposed mechanisms, the following groups face elevated theoretical risk from follistatin exposure. This applies to injectable fragment products, gene-therapy approaches, or any other modality that substantially elevates follistatin activity:

• Individuals with active or suspected cancer, particularly ovarian cancer, prostate cancer, or any malignancy in which activin may play a tumor-suppressive role. Follistatin's activin inhibition could theoretically interfere with anti-tumor mechanisms or chemotherapy efficacy, as suggested by the 2023 Clinical Cancer Research findings from Cole, Panesso-Gómez, and colleagues.
• Individuals with existing cardiovascular disease or cardiomyopathy. Given evidence from Biesemann and colleagues in 2014 that myostatin plays a role in cardiac energy homeostasis, systemic myostatin inhibition may carry uncharacterized cardiac risks.
• Women of reproductive age with fertility concerns. Follistatin was originally identified as an activin inhibitor regulating FSH and reproductive axis signaling; sustained follistatin elevation could disrupt gonadotropin regulation and menstrual cycle function.
• Pregnant or breastfeeding individuals. No safety data exists for these populations; the compound's activity in developmental contexts is unstudied in humans.
• Competitive athletes subject to anti-doping testing. Follistatin falls under WADA's S4 hormone and metabolic modulator category and the gene-doping prohibition as of 2026.
• Anyone considering products sold through unregulated online vendors. Identity, purity, and dosing of such products cannot be verified, and contamination and misidentification have been documented across the unregulated peptide market.

The Clinical Track Record of Myostatin Inhibition in Humans

Understanding follistatin's research context requires acknowledging the broader record of pharmaceutical myostatin inhibition. Multiple companies have developed selective anti-myostatin antibodies and related biologics — including bimagrumab, landogrozumab, and domagrozumab — as potential therapies for sarcopenia and muscle disease. A 2015 randomized, double-blind, placebo-controlled Phase 2 trial in The Lancet Diabetes and Endocrinology by Becker and colleagues enrolled 201 adults aged ≥75 with recent falls and low muscle strength (placebo n=99, LY2495655 n=102), who received subcutaneous LY2495655 315 mg or placebo at weeks 0, 4, 8, 12, 16, and 20, with follow-up to week 24. Appendicular lean body mass increased by a mean 0.43 kg more with LY2495655 than placebo (95% CI 0.19–0.66, p<0.0001). Functional gains were smaller and mixed: 12-step stair climb time improved by 1.28 s (p=0.011), chair rise with arms by 4.15 s (p=0.054), and fast gait speed by 0.05 m/s (p=0.088). Injection-site reactions were more frequent with LY2495655 (30% vs 9%, p<0.0001). Subsequent larger trials of this class (including bimagrumab and domagrozumab) have similarly shown lean-mass increases without consistent functional benefit in sarcopenia populations — suggesting the myostatin pathway has a more complex role in human muscle physiology than the foundational rodent data implied. Chen and colleagues, publishing in PNAS in 2017, provided mechanistic context by demonstrating that activin A — not myostatin alone — was the primary driver of muscle wasting in several pathological contexts, which helps explain why follistatin, which blocks both, has shown more dramatic effects in animal models than selective myostatin antibodies. The broader translational gap between dramatic rodent results and modest or mixed human outcomes is a persistent feature of this research area.

Follistatin and the Reproductive Axis

Follistatin's original characterization as an activin-binding protein in the ovarian follicle connects it to reproductive physiology in ways that are clinically relevant and often overlooked in muscle-focused discussions. Activin stimulates FSH secretion from the pituitary; follistatin inhibits activin and thereby suppresses FSH. Perakakis and colleagues characterized the physiology of the activin–follistatin system in humans in a 2018 paper in the Journal of Clinical Endocrinology and Metabolism, documenting associations with metabolic and anthropometric variables and demonstrating that follistatin rises measurably in response to acute exercise — a finding extended by Hansen and colleagues in Endocrinology in 2011, who reported that exercise induces a marked rise in plasma follistatin and proposed it functions as a contraction-induced hepatokine. Hansen and Plomgaard published further clarification in Molecular and Cellular Endocrinology in 2016 showing that circulating follistatin is primarily liver-derived and regulated by the glucagon-to-insulin ratio, framing follistatin as a metabolic as well as reproductive signaling molecule. In women, sustained pharmacologic elevation of follistatin would be expected to alter gonadotropin secretion and reproductive hormone patterns; this effect is not studied in the context of exogenous follistatin administration.

Biomarkers Relevant to Muscle Biology

For anyone interested in the biology of muscle hypertrophy, muscle loss, or the myostatin pathway, establishing a biomarker baseline provides objective context. Follistatin's proposed mechanisms connect to several measurable markers:

• Insulin-like growth factor 1 (IGF-1): IGF-1 is the primary anabolic mediator downstream of growth hormone and the most clinically relevant marker of the somatotropic axis. Because follistatin and IGF-1 both influence muscle mass through overlapping satellite cell biology, IGF-1 levels provide baseline context for an individual's growth factor environment.
• Follicle-stimulating hormone (FSH) and luteinizing hormone (LH): Because follistatin was originally characterized as an FSH-suppressing protein through activin inhibition, FSH and LH levels reflect the reproductive axis that follistatin regulates. Baseline gonadotropin measurements are relevant for anyone considering interventions in the activin–follistatin pathway, particularly women of reproductive age.
• High-sensitivity C-reactive protein (hs-CRP): Systemic inflammation is a driver of muscle catabolism and sarcopenia, operating partly through the same TGF-beta and cytokine pathways that follistatin intersects. A baseline hs-CRP characterizes the inflammatory environment and provides context for any intervention targeting muscle maintenance. Reference ranges vary by lab and individual; a provider will interpret results in the context of the full clinical picture.
• Creatine kinase (CK) and muscle enzymes: CK is the primary marker of muscle cell integrity. Elevated CK indicates muscle breakdown and is relevant when evaluating any intervention that claims to alter muscle biology, whether by increasing anabolism or reducing catabolism.
• Testosterone and sex hormone panel: Testosterone is the primary androgen regulating muscle protein synthesis and is relevant to any anabolic pathway discussion. It interacts with the same downstream mTOR and satellite cell signaling pathways that follistatin influences. A full evaluation of muscle physiology should include testosterone, free testosterone, and SHBG to characterize the androgenic context. Additional context on the hormonal biomarker cluster is available through Superpower's strength and resilience biomarker guide.
• Inflammatory and recovery markers: Muscle recovery biology overlaps substantially with the activin–myostatin axis. The inflammation and muscle recovery biomarker panel provides a structured set of markers for evaluating the post-exercise and anabolic-catabolic balance in skeletal muscle. Reference ranges vary by lab and individual; a qualified provider will interpret results in the context of training history, age, and clinical presentation.
• Comprehensive metabolic panel and organ function: Because follistatin is liver-derived and regulated by metabolic signals — the glucagon-to-insulin ratio, as established by Hansen and Plomgaard in Molecular and Cellular Endocrinology in 2016 — liver function markers and fasting metabolic indicators provide context for endogenous follistatin physiology and for evaluating general safety before any investigational intervention.

When to Take This Seriously

If you are dealing with muscle loss, impaired recovery, or sarcopenia-related concerns, those are real clinical problems with established evaluation pathways. A primary care provider, sports medicine physician, or endocrinologist can assess muscle health through history, examination, and targeted bloodwork. Understanding your IGF-1, testosterone, inflammatory markers, and metabolic baseline through bloodwork provides objective evidence of where anabolic and catabolic forces actually stand — which is the necessary starting point for any rational clinical decision. Investigating a compound with dramatic animal data but no human efficacy trials, manufactured under unknown conditions, is not the same as addressing the underlying biology.

That commitment to objective data before clinical decisions is what drives Superpower's approach to preventive health: the belief that understanding your biology through measurable markers is the foundation for every health decision, whether you are exploring established therapies or following emerging research into compounds like follistatin.

IMPORTANT SAFETY INFORMATION

Follistatin is not FDA-approved for any indication in any formulation. Follistatin gene therapy (AAV1-FS344) is an investigational compound available only through registered clinical trials. Injectable follistatin peptide fragments have no FDA-approved pathway, no established human pharmacokinetics, and no human clinical efficacy data. Superpower Health does not prescribe, sell, compound, or facilitate access to follistatin in any form. This page is provided for educational and informational purposes only.

Warnings: Theoretical cardiac risk based on myostatin's role in cardiac energy homeostasis as described by Biesemann and colleagues in Circulation Research in 2014; theoretical cancer-promotion or chemotherapy-resistance risk based on follistatin's activin-inhibitory activity as described by Cole and colleagues in Clinical Cancer Research in 2023; reproductive axis disruption (FSH and gonadotropin suppression) with sustained activin inhibition; unknown contamination, identity, and dosing consistency from unregulated online sources.

Populations with elevated theoretical risk: individuals with active or suspected cancer; individuals with cardiovascular disease or cardiomyopathy; women of reproductive age with fertility concerns; pregnant or breastfeeding individuals; competitive athletes subject to WADA anti-doping regulations.

As of April 2026, no human efficacy data exists for injectable follistatin fragments. Long-term safety data is entirely absent for this route of administration. The only human evidence pertains to intramuscular gene therapy in specific neuromuscular disease populations, which is mechanistically and pharmacologically distinct from injectable peptide products.

As of the 2026 WADA Prohibited List, follistatin is prohibited in competition under S4 (hormone and metabolic modulators) and the gene-doping prohibition. Athletes should consult their governing body before any exposure.

Additional Questions

What did the follistatin gene therapy trials find in humans?

The Phase 1/2a trial published by Mendell and colleagues in Molecular Therapy in 2015 enrolled six Becker muscular dystrophy patients who received bilateral intramuscular AAV1-FS344 injections into the quadriceps. Four of six patients showed improvement in six-minute walk distance at 180 days. A separate 2017 study by the same group examined six sporadic inclusion body myositis patients and reported functional improvement at one year. Both studies were small, open-label, and uncontrolled; they establish preliminary safety signals and a direction for further investigation, not clinical efficacy in the regulatory sense.

Is follistatin on the WADA Prohibited List?

Yes. As of the 2026 WADA Prohibited List, follistatin and myostatin-pathway inhibitors are covered under the S4 (hormone and metabolic modulators) category and by the gene-doping prohibition. Athletes subject to anti-doping regulations should treat any follistatin-related product as prohibited and consult their governing body or a qualified anti-doping advisor before any exposure.

Could follistatin have any cancer-related risks?

This is a recognized concern in the research literature. Cole, Panesso-Gómez, and colleagues, publishing in Clinical Cancer Research in 2023, reported that quiescent ovarian cancer cells secrete follistatin to induce chemotherapy resistance, implicating elevated follistatin in tumor cell survival. Because activin, which follistatin inhibits, has antiproliferative activity in certain tissue contexts, chronic pharmacologic suppression of activin through follistatin elevation raises a theoretical concern about tumor promotion or reduced chemotherapy efficacy. This risk has not been characterized in humans using exogenous follistatin, but individuals with active malignancy or cancer history should be aware of it.