YK-11: a steroidal compound sold as a SARM, what is actually known

"What is YK11", "does YK11 work" and "is YK 11 safe" are the questions people bring to this compound, and they deserve a straight answer: almost nothing is known. YK-11 has the thinnest evidence base of any compound commonly sold as a SARM. It has never been given to a human being in a clinical study. Everything written about its effects in people is extrapolated from cell-culture experiments, a handful of rodent studies and the anti-doping literature. This guide sets out exactly what those papers found, why YK-11's chemistry sets it apart from non-steroidal SARMs, and where it stands under UK, EU and US law and the WADA Prohibited List. It contains no guidance on use. YK-11 is sold on this site for laboratory research only.

What is YK-11?

YK-11 is a synthetic steroid. Its full chemical name is (17alpha,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxo-19-norpregna-4,20-diene-21-carboxylic acid methyl ester, which tells a chemist three things: it is built on a 19-nor steroid skeleton, the same family as nandrolone; it carries an unusual orthoester group at the 17 position; and it is an ester that is likely to be broken down in the body. It was first described in 2011 by Yuichiro Kanno and colleagues at Toho University in Japan, who were screening steroid derivatives for androgen receptor activity (Kanno et al., 2011).

It has never been developed by a pharmaceutical company, never entered a clinical trial and never been the subject of a toxicology programme. By 2018 it had been detected in a seized black-market product, and the Cologne anti-doping laboratory described it as an experimental drug candidate and a non-approved substance for humans about which scientific data on metabolism are scarce (Piper et al., 2018). Calling it a SARM is a marketing convention; pharmacologically it is a steroidal androgen receptor partial agonist. Our overview What Are SARMs? explains why the steroidal versus non-steroidal distinction matters.

Mechanism of action

In a luciferase reporter assay, YK-11 activated the androgen receptor but only partially compared with dihydrotestosterone (DHT). It accelerated movement of the receptor into the nucleus, but it did not induce the amino/carboxyl-terminal (N/C) interaction within the receptor that full agonists produce, and it blocked DHT from inducing it (Kanno et al., 2011). The authors suggested this explained its partial agonism and proposed that it "might" act as a SARM. That is the origin of the SARM label: a suggestion in the final sentence of a cell-culture paper.

The "myostatin inhibitor" claim comes from a second cell-culture paper. In C2C12 mouse myoblasts, YK-11 induced expression of follistatin, a protein that binds and neutralises myostatin, whereas DHT did not; blocking follistatin with an antibody reversed the effect of YK-11 on differentiation (Kanno et al., 2013). This is an indirect mechanism observed in a dish, and it has never been examined in people. A third paper from the same group showed that YK-11 and DHT accelerated proliferation and mineralisation in MC3T3-E1 mouse osteoblast cells, with increases in osteoprotegerin and osteocalcin and activation of Akt signalling (Yatsu et al., 2018).

What the research reports

Cell-culture studies

The three Toho University papers described above are the core of the laboratory evidence. They are competent work, but their limitations should be stated plainly: they are in vitro, in mouse cell lines, from a single research group, and effects in a cell line at micromolar concentrations do not predict what happens in a whole organism. The same laboratory later reported that YK-11 and DHT recruited the androgen receptor to different gene regions in a human breast cancer cell line, which is a mechanistic finding rather than evidence of any effect in people.

Animal studies

A small number of rodent studies have been published, and they point in different directions. Two come from a Brazilian group that gave rats YK-11 for five weeks, with or without swimming exercise, and examined the hippocampus, a brain region central to memory. In the first, YK-11 increased oxidative stress and impaired markers of mitochondrial function in the hippocampus; exercise prevented some of these changes but not most of them (Dahleh et al., 2023). In the second, computer modelling predicted high brain permeability, and in the rats YK-11 impaired consolidation of aversive memory, downregulated BDNF/TrkB/CREB signalling, raised the pro-inflammatory cytokines IL-1beta and IL-6, lowered the anti-inflammatory IL-10 and activated the p38 MAPK apoptotic cascade (Dahleh et al., 2024). The authors concluded that YK-11 "significantly alters hippocampal neurochemistry" and that this "challenges common perceptions of their minimal side effects".

Two other studies examined disease models. In mice infected with gram-negative bacteria, a Korean group reported that YK-11 lowered inflammatory cytokines and organ damage markers and reduced mortality from sepsis (Lee et al., 2021). A Chinese group reported that YK-11 promoted bone-forming differentiation of rat bone marrow stem cells in culture, and that a hydrogel containing YK-11 applied directly to a skull defect in rats promoted repair (Wang et al., 2025). Both are single, unreplicated studies in artificial injury or infection models, and local application to bone says nothing about whole-body exposure. None of the published abstracts reports hormone levels or fertility outcomes, and none of the studies lasted longer than a few weeks.

Anti-doping and metabolism

The Cologne laboratory administered deuterium-labelled YK-11 in an elimination study and identified fourteen urinary metabolites. No intact YK-11 was found in urine at all, confirming that the ester and orthoester groups are broken down in the body. Unconjugated metabolites disappeared within 24 hours, while glucuronidated and sulfated metabolites remained detectable for more than 48 hours (Piper et al., 2018). A UK study involving the British Horseracing Authority gave YK-11 orally to two horses and detected the parent compound in plasma, together with several metabolites in plasma and urine (Harding et al., 2023). Mass spectrometric characterisation for doping control had been published the previous year (Thevis et al., 2017), and a 2024 paper reported the detection of YK-11 in a real doping control sample (Sobolevsky et al., 2024). Nothing is published on whether the metabolites are active. Apart from a docking prediction that YK-11 may inhibit 5-alpha-reductase type II (Dahleh et al., 2024), its interaction with steroid-metabolising enzymes has not been measured.

What is not known

There is no human pharmacokinetic data and no human safety data. We found no study designed to assess effects on the liver, lipids, testosterone production, fertility, heart or prostate in any species, and no long-term animal study. Because YK-11 is a steroid, it cannot be assumed to lack the class effects of 19-nor steroids, including suppression of the body's own hormone production, but this has not been measured. Surveys of SARM users report that more than half experience side effects such as mood swings, decreased testicular size and acne (Efimenko et al., 2022), but those surveys do not separate YK-11 from other compounds, and the products involved were of unknown content. When 44 products sold online as SARMs were analysed, only 52 per cent contained any SARM and only 41 per cent matched the label (Van Wagoner et al., 2017). Nothing here is a claim about any product on this site. Products are for laboratory research only and have not been tested for any effect in people.

Regulatory status

United Kingdom

YK-11 is not a licensed medicine and has never been assessed by the MHRA. It is not an authorised food supplement or novel food and may not be sold or marketed for consumption. Its position under the Misuse of Drugs Act 1971 is less straightforward than for non-steroidal SARMs. Anabolic steroids are Class C drugs, and the Act's Schedule 4 Part II includes both named steroids and a generic definition covering compounds structurally derived from certain steroid cores by specified modifications. Because YK-11 has a 19-nor steroid skeleton, it cannot be assumed to sit outside that generic definition, and we are not aware of any published official guidance that settles the question. Buyers should understand that the compound's legal position is less clear than that of the non-steroidal SARMs, and that Free Muscle supplies it, like the rest of the range, solely as a research chemical to adults aged 18 and over. The brands held are compared in the YK-11 collection.

European Union

There is no EU marketing authorisation or novel food authorisation. Several member states control anabolic steroids by structure, and a steroidal compound such as YK-11 may be treated differently from non-steroidal SARMs. Buyers in EU countries are responsible for their own national import rules.

United States

The FDA has not approved YK-11 and has warned against products containing SARMs. YK-11 is not specifically listed under the US Anabolic Steroid Control Act, although that legislation also allows classification of unnamed compounds by structure.

WADA and sport

YK-11 is prohibited at all times under section S1 of the WADA Prohibited List, anabolic agents. Whether it is categorised as a SARM or as a steroid makes no practical difference: it is banned, and laboratories have validated methods for its metabolites (Piper et al., 2018; Sobolevsky et al., 2024). In the Cologne elimination study, conjugated metabolites were still detectable after more than 48 hours; beyond that, the window is not established in a verified source.

Common questions

What is YK-11 used for?

It has no approved or investigational medical use. It has been used as a laboratory tool for studying androgen receptor signalling, in a few rodent disease models, and as a target compound in anti-doping research.

Is YK-11 a SARM or a steroid?

Chemically it is a steroid, a 19-nor pregnane derivative. Functionally it is a partial agonist of the androgen receptor. It was labelled a SARM because of its partial agonism in a reporter assay, not because it belongs to the non-steroidal chemical class that the term usually describes.

Does YK-11 work, and how long does it take to work?

These are questions about use in people, which we do not advise on and on which there is no evidence. No human has been studied. The cell-culture results cannot be translated into any statement about people.

Is YK-11 safe?

Nobody knows, because it has never been tested. Two rat studies found oxidative stress, inflammatory and apoptotic changes in the brain. We do not describe any research compound as safe.

YK-11 dosage, half-life, before and after, results, injectable

We do not publish dosing, cycle or outcome guidance and we make no claims about what YK-11 does in people. No human half-life has been measured. There is no published data on any injectable form. Products here are sold for research.

YK-11 vs RAD-140 or LGD-4033

RAD-140 and LGD-4033 are non-steroidal and have at least some human data: a phase 1 cancer trial for RAD-140 and a 21-day healthy volunteer trial for LGD-4033. YK-11 is steroidal and has none. All three are WADA-prohibited and unlicensed. See the RAD-140 and LGD-4033 collections.

Is YK-11 legal in the UK?

It is sold as a research chemical to adults and is not a licensed medicine. Its status under the Misuse of Drugs Act is discussed above and is less clear than for non-steroidal SARMs. It is banned in sport.

How to verify a batch

With a compound this poorly characterised, batch testing is the only objective information available about what is in the pack. A certificate of analysis for the specific batch should show identity by HPLC or LC-MS against a YK-11 reference standard, purity as a percentage, the measured content per unit against the stated strength, a batch number that matches the pack, a test date and the name of an independent laboratory. Identity matters particularly here, because mislabelling and substitution are documented across products sold as SARMs (Van Wagoner et al., 2017).

Every Free Muscle-brand batch is assayed by Janoshik Analytical, and the certificate for your batch is sent on request by email. For other brands on Muscle Market, a certificate is shown only where the manufacturer supplies one for the batch held. A generic PDF with no batch number is not a batch certificate. Read How to Read a Certificate of Analysis, What Is Janoshik Analytical? and the lab tests page.

Related reading

YK-11 is sold for laboratory research use only. It is not a licensed medicine, has not been evaluated by the MHRA, EMA or FDA, is not a food supplement and is not for human consumption. Products are supplied to adults aged 18 and over. Nothing on this page is medical advice or dosing, cycle or usage guidance. Summaries of published studies describe what researchers reported in cell cultures, animals and anti-doping work and are not claims about any product.

References

  1. Kanno Y, et al. (17alpha,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. PMID: 21372378.
  2. Kanno Y, et al. Selective androgen receptor modulator, YK11, regulates myogenic differentiation of C2C12 myoblasts by follistatin expression. Biol Pharm Bull. 2013;36(9):1460-1465. PMID: 23995658.
  3. Yatsu T, 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. PMID: 29491216.
  4. Dahleh MMM, 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. PMID: 38521455.
  5. Piper T, 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. PMID: 30379415.
  6. Thevis M, et al. Mass spectrometric characterization of the selective androgen receptor modulator (SARM) YK-11 for doping control purposes. Rapid Commun Mass Spectrom. 2017;31(14):1175-1183. PMID: 28440570.
  7. Sobolevsky T, et al. Detection of selective androgen receptor modulator YK-11 in a doping control sample. Drug Test Anal. 2024;16(6):655-660. PMID: 37946705.
  8. Efimenko IV, et al. Adverse effects and potential benefits among selective androgen receptor modulators users: a cross-sectional survey. Int J Impot Res. 2022;34(8):757-761. PMID: 34471228.
  9. Van Wagoner RM, 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. PMID: 29183075.
  10. Dahleh MMM, 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. PMID: 37468001.
  11. Lee SJ, et al. Myostatin inhibitor YK11 as a preventative health supplement for bacterial sepsis. Biochem Biophys Res Commun. 2021;543:1-7. PMID: 33588136.
  12. Wang R, et al. YK11 promotes osteogenic differentiation of BMSCs and repair of bone defects. J Mol Endocrinol. 2025;74(2):e240073. PMID: 39660819.
  13. Harding C, 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. PMID: 36519889.