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Follistatin

Grade C: Preliminary or limited human evidence

TL;DR: Grade C: human studies exist, but the evidence does not support exogenous follistatin protein injection specifically. The human data comes from AAV-mediated gene therapy trials in rare muscle diseases (Becker muscular dystrophy, inclusion body myositis), which deliver a follistatin gene into muscle cells, a fundamentally different intervention than injecting follistatin protein. Critically, citations labeled as RCTs in this compound's database are trials where follistatin was measured as a biomarker following exercise or creatine supplementation, not trials testing follistatin as an intervention. There are no published human trials testing exogenous follistatin protein administration for any indication. The grade reflects the human gene therapy data as limited contextual evidence, not direct evidence for injected follistatin.

Key Takeaways

  • Grade C: Preliminary or limited human evidence
  • Not FDA approved: Not FDA-approved for any indication. The only human-relevant data involves gene therapy (AAV vector delivery), which follows a biologics regulatory pathway entirely separate from compounded peptides. No IND application for exogenous follistatin protein administration has been publicly disclosed. Classified as an unapproved drug substance.
  • Compounding: Its federal compounding status is not separately established in the FDA bulk-substance lists we verify; confirm current status with a licensed pharmacist or physician before any use.

Mechanism

Follistatin is an endogenous glycoprotein that binds and neutralizes several members of the TGF-beta superfamily of signaling proteins, most prominently myostatin (GDF-8) and activin A. Myostatin is a negative regulator of skeletal muscle mass; individuals with naturally occurring loss-of-function myostatin mutations develop extraordinary muscle hypertrophy. By blocking myostatin and activin signaling, follistatin promotes muscle growth and regeneration in preclinical models. It also plays roles in reproductive biology, hair follicle cycling, and other developmental processes, inhibiting its endogenous counterparts systemically may have wide-ranging effects beyond muscle.

Evidence

Grade C: human studies exist, but the evidence does not support exogenous follistatin protein injection specifically. The human data comes from AAV-mediated gene therapy trials in rare muscle diseases (Becker muscular dystrophy, inclusion body myositis), which deliver a follistatin gene into muscle cells, a fundamentally different intervention than injecting follistatin protein. Critically, citations labeled as RCTs in this compound's database are trials where follistatin was measured as a biomarker following exercise or creatine supplementation, not trials testing follistatin as an intervention. There are no published human trials testing exogenous follistatin protein administration for any indication. The grade reflects the human gene therapy data as limited contextual evidence, not direct evidence for injected follistatin.

Safety and risks

No human safety data exists for exogenous follistatin protein injection. Risks are inferred from its mechanism. Follistatin is a broad inhibitor of activins and other TGF-beta superfamily members; sustained systemic suppression of activins could disrupt the hypothalamic-pituitary-gonadal axis, potentially impairing fertility and reproductive hormone balance. Follistatin also inhibits myostatin, unregulated muscle hypertrophy signaling carries unknown long-term cardiac and metabolic consequences. In the gene therapy trials, one study reported a notable frequency of falls without adequate safety characterization. Products sold as 'follistatin-344' have been detected on the black market with unverified purity; a published detection study confirmed that black-market follistatin products exist and their composition is unreliable.

Interactions

No human interaction data. Follistatin's inhibition of activin A could theoretically interact with treatments relying on TGF-beta signaling, including certain cancer therapies and immunomodulatory agents. Gonadotropin-based fertility treatments could be affected given activin's role in FSH regulation. These are theoretical inferences only.

Compounding legality

Its federal compounding status is not separately established in the FDA bulk-substance lists we verify; confirm current status with a licensed pharmacist or physician before any use.

Sources

  1. Inhibition of myostatin with emphasis on follistatin as a therapy for muscle disease. (2009) review
  2. Myostatin and follistatin as monitoring and prognostic biomarkers in dysferlinopathy. (2023) other
  3. Relationship of muscle function to circulating myostatin, follistatin and GDF11 in older women and men. (2018) other
  4. Combined resistance exercise and essential amino acid intake enhance follistatin/myostatin ratio and muscle fitness in older women: a randomized controlled trial. (2026) rct
  5. Time-specific effects of acute eccentric exercise on myostatin, follistatin and decorin in the circulation and skeletal muscle in rats. (2022) other
  6. Discovery of a follistatin-derived myostatin inhibitory peptide. (2020) other
  7. Follistatin-mediated skeletal muscle hypertrophy is regulated by Smad3 and mTOR independently of myostatin. (2012) other
  8. Follistatin alters myostatin gene expression in C2C12 muscle cells. (2004) other
  9. Effect of high-intensity interval training and resistance training on the follistatin and myostatin levels in gastrocnemius muscle of aged female rats. (2025) other
  10. Deletion of fibro-adipogenic progenitors-specific follistatin impairs muscle function and accelerates skeletal muscle atrophy in obese mice. (2025) other
  11. Serum Myostatin and Follistatin Levels in Patients With Dermatomyositis and Polymyositis. (2022) other
  12. A comparative study of myostatin, follistatin and decorin expression in muscle of different origin. (2011) other
  13. The effects of resistance training on myostatin and follistatin in adults: A systematic review and meta-analysis. (2023) review
  14. Improvement in Skeletal Muscle Strength and Plasma Levels of Follistatin and Myostatin Induced by an 8-Week Resistance Training and Epicatechin Supplementation in Sarcopenic Older Adults. (2019) rct
  15. Effects of the activin A-myostatin-follistatin system on aging bone and muscle progenitor cells. (2013) other
  16. Follistatin induces muscle hypertrophy through satellite cell proliferation and inhibition of both myostatin and activin. (2009) other
  17. Follistatin-induced muscle hypertrophy in aged mice improves neuromuscular junction innervation and function. (2021) other
  18. Alterations in activin A-myostatin-follistatin system associate with disease activity in inflammatory myopathies. (2020) other
  19. Follistatin complexes Myostatin and antagonises Myostatin-mediated inhibition of myogenesis. (2004) other
  20. Myostatin and Follistatin-New Kids on the Block in the Diagnosis of Sarcopenia in IBD and Possible Therapeutic Implications. (2021) review
  21. Transgenic expression of a myostatin inhibitor derived from follistatin increases skeletal muscle mass and ameliorates dystrophic pathology in mdx mice. (2008) other
  22. Muscle follistatin gene delivery increases muscle protein synthesis independent of periodical physical inactivity and fasting. (2021) other
  23. Role of IGF-I in follistatin-induced skeletal muscle hypertrophy. (2015) other
  24. Skeletal Muscle Hypertrophy, Insulin-like Growth Factor 1, Myostatin and Follistatin in Healthy and Sarcopenic Elderly Men: The Effect of Whole-body Resistance Training. (2019) other
  25. Role of follistatin in muscle and bone alterations induced by gravity change in mice. (2018) other

Follistatin is Not FDA approved. PeptideGrids presents evidence and regulatory status for informational purposes only. We do not sell, supply, source, or help anyone obtain this compound, and we provide no dosing or administration guidance. This is not medical advice; consult a licensed clinician. Full disclaimer.

Last reviewed June 1, 2026 by PeptideGrids editorial team (independently audited).