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Comparison

Follistatin-344 vs YK-11

Both are myostatin inhibitors, so the meaningful differences are in kinetics, evidence and regulatory status.

On published evidence alone, Follistatin-344 is the better documented of the two (animal models only). That is a statement about the state of the literature, not a recommendation.

Follistatin-344 YK-11
Class Myostatin inhibitors Myostatin inhibitors
Evidence Animal models only In vitro only
Human trials ~1 None published
Half-life ~30 minutes ~6-10 hours
Reported range 100-300 mcg 5-10 mg
Frequency Once daily, short cycles Once daily
Routes Subcutaneous, Intramuscular Oral
FDA approved No No
Research use only Yes Yes
Banned in sport Yes Yes
Studied for Muscle hypertrophy research, Muscular dystrophy gene therapy research Muscle growth research
Reported side effects Injection-site reactions, Headache, Poorly characterised Hepatotoxicity, HPTA suppression, Lipid disruption, Tendon discomfort, Aggression

Follistatin-344

Follistatin-344 is a precursor isoform of the endogenous glycoprotein follistatin, which binds and neutralises activin A and myostatin. Removing myostatin inhibition permits muscle hypertrophy and hyperplasia, an effect demonstrated dramatically in gene-therapy animal models. The injectable protein is cleared within minutes and does not reproduce those results, which is the key practical caveat: the striking animal data comes from sustained genetic expression, not from injections.

YK-11

YK-11 is a synthetic steroid derived from dihydrotestosterone with a distinctive gem-dimethyl ester group. It acts as a partial androgen receptor agonist and has been reported in cell culture to increase follistatin expression, which is the basis of the myostatin-inhibitor marketing. Because it is steroidal it carries androgenic liability including hepatotoxicity and HPTA suppression, unlike the true peptides in this class. Human data is absent.

Follistatin-344 vs YK-11: common questions

What is the difference between Follistatin-344 and YK-11?

Both are myostatin inhibitors. Follistatin-344: A natural myostatin-binding glycoprotein, of interest for muscle growth but with a very short circulating half-life. YK-11: A steroidal compound marketed as a SARM and a myostatin inhibitor. It is neither a peptide nor, strictly, a SARM.

Which has stronger evidence, Follistatin-344 or YK-11?

Follistatin-344 has the stronger evidence base (animal models only, about 1 human studies) compared with YK-11 (in vitro only).

Are Follistatin-344 and YK-11 FDA approved?

Neither is FDA approved for any indication.

References

Regulatory and primary sources

  1. WADA Prohibited List ↗ · current year
  2. FDA: Unapproved drugs and "research use only" products ↗ · regulatory status of non-approved products
  3. PubChem compound record (CID 119058028) ↗ · structure, identifiers, synonyms
  4. CAS Registry Number 431579-34-9 ↗ · chemical identity

Published literature

  1. Angelidi AM, Stefanakis K, Chou SH, et al.. Relative Energy Deficiency in Sport (REDs): Endocrine Manifestations, Pathophysiology and Treatments.Endocr Rev 2024.PubMed 38488566 · doi:10.1210/endrev/bnae011
  2. Seo MW, Jung SW, Kim SW, et al.. Effects of 16 Weeks of Resistance Training on Muscle Quality and Muscle Growth Factors in Older Adult Women with Sarcopenia: A Randomized Controlled Trial.Int J Environ Res Public Health 2021.PubMed 34201810 · doi:10.3390/ijerph18136762
  3. Zhang M, Song Y, Zhu J, et al.. Effectiveness of low-load resistance training with blood flow restriction vs. conventional high-intensity resistance training in older people diagnosed with sarcopenia: a randomized controlled trial.Sci Rep 2024.PubMed 39558011 · doi:10.1038/s41598-024-79506-9
  4. Ren Y, Zhao H, Yin C, et al.. Adipokines, Hepatokines and Myokines: Focus on Their Role and Molecular Mechanisms in Adipose Tissue Inflammation.Front Endocrinol (Lausanne) 2022.PubMed 35909571 · doi:10.3389/fendo.2022.873699
  5. Vannuccini S, Clemenza S, Rossi M, et al.. Hormonal treatments for endometriosis: The endocrine background.Rev Endocr Metab Disord 2022.PubMed 34405378 · doi:10.1007/s11154-021-09666-w
  6. Bolanle IO, de Liedekerke Beaufort GC, Weinberg PD. Transcytosis of LDL Across Arterial Endothelium: Mechanisms and Therapeutic Targets.Arterioscler Thromb Vasc Biol 2025.PubMed 40013359 · doi:10.1161/ATVBAHA.124.321549
  7. Stefanakis K, Kokkorakis M, Mantzoros CS. The impact of weight loss on fat-free mass, muscle, bone and hematopoiesis health: Implications for emerging pharmacotherapies aiming at fat reduction and lean mass preservation.Metabolism 2024.PubMed 39481534 · doi:10.1016/j.metabol.2024.156057
  8. Zhuang M, Gu Y, Wang Z, et al.. Effects of 12-week whole-body vibration training versus resistance training in older people with sarcopenia.Sci Rep 2025.PubMed 40011687 · doi:10.1038/s41598-025-91644-2
  9. Thevis M, Schänzer W. Detection of SARMs in doping control analysis.Mol Cell Endocrinol 2018.PubMed 28137616 · doi:10.1016/j.mce.2017.01.040
  10. Harding C, Viljanto M, Habershon-Butcher J, et al.. Equine metabolism of the selective androgen receptor modulator YK-11 in urine and plasma following oral administration.Drug Test Anal 2023.PubMed 36519889 · doi:10.1002/dta.3425
  11. Sobolevsky T, Kucherova Y, Ahrens B. Detection of selective androgen receptor modulator YK-11 in a doping control sample.Drug Test Anal 2024.PubMed 37946705 · doi:10.1002/dta.3604
  12. Zhao W, Yin Y, Shi Z, et al.. Discovery and optimization of novel indolecarboxylic acid derivative as potent glucagon-like peptide‑1 receptor agonists.Mol Divers 2026.PubMed 40366550 · doi:10.1007/s11030-025-11213-7
  13. Lee JH, Han JH, Jung EJ, et al.. Development and validation of liquid chromatography-tandem mass spectrometry method for screening six selective androgen receptor modulators in dietary supplements.Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2021.PubMed 33934684 · doi:10.1080/19440049.2021.1906954

Literature retrieved from PubMed on October 16, 2026, favouring human studies and reviews. Numbered markers in the text show which paper supports which statement; uncited entries are background reading.

Read this first This page compares published reference data. It is not medical advice and not a recommendation to use either compound. Several compounds documented on this site are not approved for human use.