SARMs

YK-11

Updated · 22 sources · Editorial policy

YK-11 (also written YK11) is a synthetic steroid that Japanese university researchers first described in 2011 as a partial agonist of the androgen receptor. It is usually sold online as a “SARM” (selective androgen receptor modulator) or a “myostatin inhibitor,” but unlike most SARMs it has a steroid skeleton.

The single most important fact: YK-11 has never been tested in a controlled human trial. Everything known about its effects comes from cell culture, rodents and a few horse studies run for doping control. It is not approved as a drug anywhere. The FDA treats products sold as SARMs as unapproved drugs, and WADA names YK-11 on its Prohibited List.

This page summarizes what the laboratory studies, case reports and regulators report. It is for education only and is not medical advice.

Property Detail
Class Synthetic steroid described as a partial androgen receptor agonist (“steroidal SARM”)
Chemistry C₂₅H₃₄O₆, molecular weight 430.5 g/mol (PubChem)
Origin Described by researchers at Toho University, Japan, in 2011
Approval Not approved for any medical use in any country
Human dosing data None; no controlled human studies published
Half-life Not established in people; in an excretion study, unconjugated urinary metabolites disappeared within 24 h and conjugated ones stayed detectable beyond 48 h
Key mechanism finding Activates the androgen receptor without the usual N/C-terminal interaction; induced follistatin in mouse muscle cells
US status Not a scheduled controlled substance; FDA considers products marketed as SARMs unapproved new drugs
WADA status Prohibited at all times (S1.2, named as an example SARM)

What it is

YK-11’s chemical name is (17α,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxo-19-norpregna-4,20-diene-21-carboxylic acid methyl ester (Kanno et al., Biol Pharm Bull 2011). In plain terms, it is a 19-nor steroid nucleus with a bulky orthoester-type group attached to the D-ring at carbon 17. Its formula is C₂₅H₃₄O₆ and its molecular weight 430.5 g/mol (PubChem).

That steroid backbone sets it apart from the better-known nonsteroidal SARMs such as ostarine, ligandrol, RAD-140, andarine and S-23. Doping-control chemists describe the D-ring group as chemically labile (easily broken down), and expected it to be extensively metabolized in the body (Piper et al., Drug Test Anal 2018). A Korean food-safety lab reported that it breaks down by hydrolysis within a few hours during analysis of supplement samples (Lee et al., Food Addit Contam 2021).

How it acts on the androgen receptor

The androgen receptor normally changes shape when a hormone such as dihydrotestosterone (DHT) binds. Its two ends (the amino and carboxyl terminals) fold together, called the N/C interaction, which helps switch on target genes. In the 2011 cell studies, YK-11 (Kanno et al., 2011):

  • moved the androgen receptor into the cell nucleus, like a normal androgen;
  • did not trigger the N/C interaction, and blocked DHT from triggering it;
  • acted only as a partial agonist in a reporter-gene test;
  • switched on some androgen-responsive genes and not others, depending on the gene, in a human breast cancer cell line (MDA-MB-453).

A 2022 follow-up by the same group, again in MDA-MB-453 cells, found that DHT and YK-11 recruited the receptor to different gene regions and probably different helper proteins (cofactors) (Kanno et al., Exp Cell Res 2022). This gene-selective behavior is the basis for calling it a SARM. It has not been shown to translate into tissue selectivity in a living animal or a person.

About the “myostatin inhibitor” label. Sellers market YK-11 as a myostatin inhibitor (see the FDA warning letter below). The source of that claim is one 2013 cell-culture study. In mouse C2C12 myoblasts (immature muscle cells), YK-11 at 500 nM raised levels of follistatin, a protein that binds and blocks myostatin and related growth factors. DHT did not do this, and an antibody against follistatin cancelled YK-11’s effect on muscle-cell differentiation (Kanno et al., Biol Pharm Bull 2013). The study did not show that YK-11 acts on myostatin directly, and no study has measured follistatin or myostatin activity in people who took it.

For the separate research peptide, see follistatin-344.

How it behaves in the body

There are no published pharmacokinetic studies of YK-11 in humans: no measured half-life, peak level or bioavailability. The figures below come from doping-control work, which aims to find markers that can be detected, not to describe how the drug behaves at a dose.

Study Subjects and dose Main finding
Piper et al., 2018 Elimination study with deuterium-labeled YK-11; urine analyzed 14 urinary metabolites; no intact YK-11 found in urine. Unconjugated metabolites gone within 24 h; glucuronide and sulfate conjugates still detectable after 48 h
Harding et al., 2023 2 Thoroughbred horses, 50 mg orally daily for 3 days Parent YK-11 plus 7 metabolites in plasma; 11 phase I metabolites in urine

The 2018 study identified two glucuronidated 19-nor-pregnane metabolites as the most useful markers and added them to the routine test for anabolic agents (Piper et al., 2018). In 2023 the UCLA Olympic Analytical Laboratory published a report of YK-11 detected in a doping control sample (Sobolevsky et al., Drug Test Anal 2024).

About half-life figures. We found no published human measurement of YK-11’s half-life. The only data are the urinary detection windows above, which describe how long metabolites can be detected, not how long the drug stays active.

Regulatory status

  • Not an approved drug. No company has filed YK-11 for approval. The FDA states that SARMs are not FDA approved and “cannot be legally marketed in the U.S. as a dietary supplement or drug at this time” (FDA consumer update, 2023).
  • FDA enforcement. In December 2025 the FDA sent a warning letter to an online seller that listed “YK-11” (marketed as a “Myostatin Inhibitor”) among products it called unapproved new drugs. The FDA said “research-only” labels did not change this, because the website showed the products were intended for human use (FDA warning letter, Titan SARMs, 2025).
  • Not a scheduled controlled substance. YK-11 is not named in the US Schedule III list of anabolic steroids (21 CFR 1308.13).
  • Banned in sport. WADA lists YK-11 by name as an example SARM under S1.2 “Other anabolic agents,” prohibited in and out of competition (WADA 2026 Prohibited List).

What the research shows

All efficacy data are from cells or animals. None of these results has been tested in people, and doses used in cell dishes or rodents cannot be converted into a human dose.

Muscle cells

In mouse C2C12 myoblasts, YK-11 and DHT both increased myosin heavy chain, a marker of mature muscle fibers. YK-11 raised the muscle-building transcription factors MyoD, Myf5 and myogenin more than DHT did at the same 500 nM concentration. The rise in Myf5 and myogenin needed high concentrations (100 or 500 nM), and the androgen receptor antagonist hydroxyflutamide blocked the effect (Kanno et al., 2013).

No study has measured muscle mass, strength or body composition in humans taking YK-11.

Bone

Model Finding Source
Mouse MC3T3-E1 osteoblast cells Faster proliferation and mineralization, more osteoprotegerin and osteocalcin; blocked by an androgen receptor antagonist Yatsu et al., Biol Pharm Bull 2018
Bone marrow mesenchymal stem cells in culture, 0.25–4 μM More bone-forming differentiation, rising with concentration Wang et al., J Mol Endocrinol 2025
Rats with skull defects, YK-11 in a hydrogel (0.5 and 1 mg/mL) Better repair of the defect; effect suppressed when the androgen receptor was blocked Wang et al., 2025

In mice infected with gram-negative bacteria, YK-11 lowered pro-inflammatory cytokines and organ-damage markers and reduced deaths from sepsis (Lee et al., Biochem Biophys Res Commun 2021). Several of the authors were affiliated with a biotech company. This is a single mouse study and has not been replicated.

Side effects and risks

There is no controlled safety data in humans. What exists falls into three groups: rat studies, individual case reports, and regulator warnings about SARMs as a class.

Brain effects in rats

A Brazilian group gave male Wistar rats YK-11 (reported as 0.35 g/kg) for five weeks, with or without swimming exercise:

  • Oxidative stress and mitochondria: YK-11 increased oxidative stress and impaired every mitochondrial function marker measured in the hippocampus, the brain region central to memory. Exercise prevented only some of these changes (Dahleh et al., J Steroid Biochem Mol Biol 2023).
  • Inflammation and memory: YK-11 raised the inflammatory cytokines IL-1β and IL-6, lowered the anti-inflammatory IL-10, activated cell-death (apoptosis) signaling, and impaired consolidation of aversive memory (Dahleh et al., Chem Biol Interact 2024).

These are animal results at a high dose and do not show what happens in people. They do contradict the claim that YK-11 is free of off-target effects.

Liver injury

SARMs as a class have been linked to cholestatic liver injury, a pattern in which bile flow is blocked and jaundice and itching dominate. Of the SARM liver-injury cases collected in a 2023 systematic review, one involved YK-11: a 23-year-old active-duty Marine who had taken LGD-4033, RAD-140 and YK-11 for about 12 weeks developed jaundice and itching and was hospitalized (Lee et al., Mil Med 2023). A review of the case reported a peak total bilirubin of 29.2 mg/dL (Leciejewska et al., Eur J Clin Pharmacol 2024), and his tests returned to normal within a year (Vignali et al., J Xenobiot 2023). Because he took three compounds, the injury cannot be attributed to YK-11 alone.

A search of the FDA’s adverse event database (CAERS) for “YK-11” found 2 reports: hepatic failure in a 23-year-old man, and a stroke with paresthesia (abnormal skin sensations) in a 37-year-old man (Leciejewska et al., 2024). Such reports are unverified and do not prove cause.

Stroke report and FDA action

In late 2025 the FDA reported testing a product called GE Labs Ykarine after receiving a report of a consumer who used it and then had a stroke. The product contained its labeled YK-11 and also an undeclared anabolic steroid, trendione, a Schedule III substance. The FDA told consumers not to use the product (FDA, 2025).

Class warnings from the FDA

The FDA lists these potential harms for SARMs as a group (FDA):

  • increased risk of heart attack or stroke;
  • psychosis or hallucinations, and sleep disturbances;
  • sexual dysfunction, infertility and testicular shrinkage;
  • liver injury and acute liver failure;
  • pregnancy miscarriage.

No study has measured YK-11’s effect on the body’s own testosterone production, fertility, lipids or blood counts in people.

Product quality

  • Undeclared YK-11. In a 2020 survey of 60 supplements bought online or directly from international vendors, a Korean government lab found YK-11 in some products that did not list it on the label (Lee et al., 2021).
  • Hidden steroids. The FDA-tested Ykarine product also contained an undeclared Schedule III steroid (FDA, 2025).
  • SARM products in general. In a JAMA analysis of 44 products sold online as SARMs, only 52% contained a SARM, 39% contained another unapproved drug, and only 41% matched their labeled amount (Van Wagoner et al., JAMA 2017). That study did not report finding YK-11.

Key takeaways

  • No human trials. YK-11 has only been studied in cells, rodents and horses. There is no established human dose, half-life or safety profile.
  • A steroid, not a typical SARM. It has a 19-nor steroid skeleton and acts as a partial, gene-selective androgen receptor agonist in cell assays.
  • “Myostatin inhibitor” is an overstatement. It raised follistatin in mouse muscle cells; it has not been shown to inhibit myostatin in people.
  • Animal safety signals exist. Rats given YK-11 showed brain oxidative stress, inflammation and memory impairment, and human case reports include cholestatic liver injury while taking it with other SARMs.
  • Unapproved and banned in sport. The FDA treats products sold as SARMs as unapproved drugs, and WADA prohibits YK-11 at all times. Products may contain undeclared steroids.

Sources

  1. Kanno Y, Hikosaka R, Zhang SY, et al. (17α,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxo-19-norpregna-4,20-diene-21-carboxylic acid methyl ester (YK11) is a partial agonist of the androgen receptor. Biol Pharm Bull. 2011;34(3):318–323. PubMed.
  2. Kanno Y, Ota R, Someya K, et al. Selective androgen receptor modulator, YK11, regulates myogenic differentiation of C2C12 myoblasts by follistatin expression. Biol Pharm Bull. 2013;36(9):1460–1465. PubMed.
  3. Kanno Y, Saito N, Saito R, et al. Differential DNA-binding and cofactor recruitment are possible determinants of the synthetic steroid YK11-dependent gene expression by androgen receptor in breast cancer MDA-MB 453 cells. Exp Cell Res. 2022;419(2):113333. PubMed.
  4. Yatsu T, Kusakabe T, Kato K, et al. Selective androgen receptor modulator, YK11, up-regulates osteoblastic proliferation and differentiation in MC3T3-E1 cells. Biol Pharm Bull. 2018;41(3):394–398. PubMed.
  5. Wang R, Zhong Y, Du Q, et al. YK11 promotes osteogenic differentiation of BMSCs and repair of bone defects. J Mol Endocrinol. 2025;74(2):e240073. PubMed.
  6. Lee SJ, Gharbi A, Shin JE, et al. Myostatin inhibitor YK11 as a preventative health supplement for bacterial sepsis. Biochem Biophys Res Commun. 2021;543:1–7. PubMed.
  7. Dahleh MMM, Bortolotto VC, Guerra GP, et al. YK11 induces oxidative stress and mitochondrial dysfunction in hippocampus: the interplay between a selective androgen receptor modulator (SARM) and exercise. J Steroid Biochem Mol Biol. 2023;233:106364. PubMed.
  8. Dahleh MMM, Bortolotto VC, Boeira SP, et al. From gains to gaps? How selective androgen receptor modulator (SARM) YK11 impact hippocampal function: in silico, in vivo, and ex vivo perspectives. Chem Biol Interact. 2024;394:110971. PubMed.
  9. Piper T, Dib J, Putz M, et al. Studies on the in vivo metabolism of the SARM YK11: identification and characterization of metabolites potentially useful for doping controls. Drug Test Anal. 2018;10(11-12):1646–1656. PubMed.
  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;15(4):388–407. PubMed.
  11. Sobolevsky T, Kucherova Y, Ahrens B. Detection of selective androgen receptor modulator YK-11 in a doping control sample. Drug Test Anal. 2024;16(6):655–660. PubMed.
  12. 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;38(7):1075–1086. PubMed.
  13. Lee BK, Park BB, Bower RJ. Selective androgen receptor modulator-induced liver injury in active duty male. Mil Med. 2023;188(7-8):usac039. PubMed.
  14. Vignali JD, Pak KC, Beverley HR, et al. Systematic review of safety of selective androgen receptor modulators in healthy adults: implications for recreational users. J Xenobiot. 2023;13(2):218–236. PubMed; PMC.
  15. Leciejewska N, Jędrejko K, Gómez-Renaud VM, et al. Selective androgen receptor modulator use and related adverse events including drug-induced liver injury: analysis of suspected cases. Eur J Clin Pharmacol. 2024;80(2):185–202. PubMed; PMC.
  16. Van Wagoner RM, Eichner A, Bhasin S, et al. Chemical composition and labeling of substances marketed as selective androgen receptor modulators and sold via the internet. JAMA. 2017;318(20):2004–2010. PubMed.
  17. US Food and Drug Administration. Certain bodybuilding products put consumers at risk for heart attack, stroke, serious liver damage and more. Content current as of December 2, 2025. FDA.
  18. US Food and Drug Administration. Warning letter to Titan SARMs LLC, MARCS-CMS 719645. December 12, 2025. FDA.
  19. US Food and Drug Administration. FDA warns of use of selective androgen receptor modulators (SARMs) among teens, young adults. Consumer update, content current as of April 26, 2023. FDA.
  20. World Anti-Doping Agency. The 2026 Prohibited List, International Standard. In effect January 1, 2026. WADA 2026 Prohibited List.
  21. Code of Federal Regulations. 21 CFR 1308.13, Schedule III. 21 CFR 1308.13.
  22. National Center for Biotechnology Information. PubChem Compound Summary for CID 119058028, YK-11. PubChem.