Peptide & Experimental
YK-11
Steroid derivative, partial agonist at the androgen receptor (marketed as a SARM), not approved · YK11, YK 11
YK-11 is sold as a SARM and “myostatin inhibitor”, but chemically it is a steroid that only partially activates the androgen receptor. The myostatin connection comes from mouse cell cultures. There is not a single study in humans on efficacy or safety; what is documented is liver damage in case reports after combined use and conspicuous findings in the brains of rats.
What YK-11 is
YK-11 is a synthetic steroid with a 19-norpregnane backbone. In research it has been described as a partial agonist at the androgen receptor; doping analysts explicitly call it a steroidal SARM. It is not approved anywhere, and there is no registered clinical trial. Doping laboratories identified it in a confiscated black-market product.
What is rated is the state of knowledge. For YK-11 it is very thin: cell experiments, animal experiments, doping analysis and case reports. Related substances with somewhat more data are Ostarine and RAD140.
How it works
In mouse muscle precursor cells (C2C12), YK-11 promoted maturation into muscle cells; key regulators of muscle formation rose more than under DHT. Unlike DHT, YK-11 triggered the production of follistatin, and an antibody against follistatin abolished the effect (Kanno 2013). Follistatin binds myostatin, the body’s own brake on muscle growth; this is where the marketing as a myostatin inhibitor comes from. More on this signaling pathway can be found in the entry Follistatin / myostatin inhibitors.
In mouse bone cells, YK-11 promoted growth and mineralization; an androgen receptor blocker weakened this (Yatsu 2018). In the body, YK-11 is extensively metabolized: in an excretion study, no unchanged YK-11 was found in the urine, but 14 breakdown products (Piper 2018). Whether any of the cell effects occur in human muscle has not been studied.
What is well supported
- That there is no human study. No study on YK-11 is registered at ClinicalTrials.gov; data on efficacy or safety in humans do not exist.
- The cellular mechanism. In mouse cells, YK-11 partially activates the androgen receptor and increases follistatin; the muscle effect in cell culture demonstrably depends on this (Kanno 2013).
- Detectability in sport. Conjugated breakdown products are detectable in urine for more than 48 hours and have been included in routine testing for anabolic agents (Piper 2018).
- The legal situation. YK-11 is listed by name in the annex of the German Anti-Doping Act.
What the studies show
Kanno 2013: mouse muscle cells
Kanno 2013 (Biol Pharm Bull) treated C2C12 muscle precursor cells with YK-11 or DHT. Under YK-11, MyoD, Myf5 and myogenin rose more, and only YK-11 triggered the production of follistatin. An antibody against follistatin reversed the muscle cell maturation. This is the basis of the myostatin narrative, measured in a mouse cell line.
Yatsu 2018: mouse bone cells
In MC3T3-E1 bone cells, YK-11 and DHT accelerated growth and mineralization, and markers such as osteoprotegerin and osteocalcin rose. An androgen receptor blocker weakened the effects.
Dahleh 2023 and 2024: rat hippocampus
Male Wistar rats received YK-11 for 5 weeks, in some cases combined with swim training. YK-11 increased oxidative stress and disrupted mitochondrial function in the hippocampus; training prevented only part of this (Dahleh 2023). In the follow-up study, the inflammatory messengers IL-1β and IL-6 rose, IL-10 fell, cell death pathways were activated, and the consolidation of a fear memory was impaired (Dahleh 2024). These are animal data; they show a possible risk, not a finding in humans.
Lee 2023 and reporting data: liver
A 23-year-old US soldier developed cholestatic liver injury with jaundice and itching after LGD-4033, RAD140 and YK-11, was treated as an inpatient and was unfit for duty until he recovered (Lee 2023). Which of the three substances was responsible cannot be separated. In the US adverse event database for dietary supplements, an analysis on YK-11 found a 23-year-old man with liver failure, classified as life-threatening (Leciejewska 2024); whether this is the same case is unclear. For the SARM class as a whole, a systematic review counted 15 case reports of liver damage in healthy users (Vignali 2023).
Where the data stop
- Muscle building in humans. Not studied. The follistatin effect has only been measured in cell culture.
- Effects on the hormonal axis, blood lipids and the heart. For YK-11 there are no measurements in humans on this.
- Safety with single-substance use. The liver cases involve combined use or reports without assessment of causality; no frequency can be derived from them.
- What is in the product. The quality of SARM products on the market is unverified, which makes attributing harm even more difficult (Leciejewska 2024). More on this in the glossary under gray market.
Status, approval and legal
YK-11 is not an approved medicine in Germany, the EU or the US; there is no registered clinical trial.
In the German Anti-Doping Act, YK-11 is listed by name in the annex under I.2, selective androgen receptor modulators. This means that acquiring, possessing and bringing into the country non-small quantities for doping in sport is prohibited (§ 2 (3)), as are manufacturing, trading and supplying it for doping purposes (§ 2 (1)).
In sport, YK-11 is prohibited at all times as an anabolic agent (WADA, S1.2); doping laboratories have developed their own detection methods (Thevis 2017; Piper 2018).
Safety
Controlled safety data do not exist. What is available is liver damage in case reports and reporting data, mostly after combined use with other SARMs, as well as animal findings in the brain. In the case reports, jaundice and itching were the main features; anyone who notices such symptoms should have them checked by a physician and disclose the use.
For the SARM class, a systematic review also describes an Achilles tendon rupture and a case of muscle breakdown in case reports, as well as elevated liver values in an average of 7.1 percent of participants in clinical trials of other SARMs (Vignali 2023). Whether this applies to YK-11 is unclear.
BK-Score Not studied in humans
| Human evidence | 1 | |
|---|---|---|
| Mechanism | 5 | |
| Safety data | 1 | |
| Hype gap | 1 | |
| Track record of use | 3 |
Evidence 1, because there is no efficacy study in humans and no registry entry for YK-11; the human data are limited to doping analysis and case reports. Mechanism 5, because the partial activation of the androgen receptor and the production of follistatin have only been shown in mouse cell cultures (Kanno 2013; Yatsu 2018), and it is unclear whether this happens in human muscle. Safety 1, because there are no controlled safety data; what is documented is liver damage after combined use with two other SARMs (Lee 2023), a report of liver failure in the US database (Leciejewska 2024) and damage in the hippocampus of rats (Dahleh 2023). Hype 1, because YK-11 is sold as a myostatin inhibitor although this effect has never been measured outside cell culture. Use 3, because YK-11 has been circulating in strength sports for some years but has never been used under medical supervision. Direction open: human data for the advertised effect are missing.
The score rates the state of knowledge, not the substance. “Safety data 9” means well studied – not harmless. “Track record of use 9” means used long and widely – that is not proof of efficacy.
Subjective assessment by Biohacking Kompakt based on published scoring rules – not a scientific rating and not a medical recommendation. Rules and all ratings (German)
Frequently asked questions about YK-11
Is YK-11 a myostatin inhibitor?
Only in cell culture. In mouse muscle precursor cells, YK-11 increased the production of follistatin, which binds myostatin. Whether this happens in human muscle has not been studied.
Is YK-11 a SARM or a steroid?
Chemically, a steroid with a 19-norpregnane backbone that only partially activates the androgen receptor. Doping analysts describe it as a steroidal SARM.
Are there studies in humans?
No. No study is registered at ClinicalTrials.gov. There are cell experiments, animal experiments, analyses for doping controls and case reports.
Does YK-11 harm the liver?
Case reports point in that direction: a 23-year-old soldier developed cholestatic liver injury after YK-11 combined with two other SARMs, and the US adverse event database records a case of liver failure after YK-11. No frequency can be derived from this.
Is YK-11 legal in Germany?
It is not an approved medicine. YK-11 is listed by name in the German Anti-Doping Act: acquiring and possessing non-small quantities for doping in sport is prohibited, as are trading and supplying it for doping purposes. In sport it is prohibited at all times under the WADA list.
Related
- Related topicRAD140 (Testolone)
- Related topicS-23
- Related topicMethylstenbolone
- Related topicBoldenone (Equipoise)
- Related topicAndarine (S-4)
- Related topicMethandrostenolone (Dianabol)
Sources
- Kanno Y et al., Biol Pharm Bull 2013 – YK11 controls muscle cell maturation in C2C12 cells via follistatin
- Yatsu T et al., Biol Pharm Bull 2018 – YK11 promotes bone cells (MC3T3-E1)
- Piper T et al., Drug Test Anal 2018 – metabolism of YK11 and metabolites for doping controls
- Thevis M et al., Rapid Commun Mass Spectrom 2017 – YK-11 for doping controls, SARMs banned by WADA
- Lee BK et al., Mil Med 2023 – SARM-induced liver injury in an active-duty soldier (LGD-4033, RAD140, YK11)
- Leciejewska N et al., Eur J Clin Pharmacol 2024 – SARM side effects and liver damage, analysis of suspected cases
- Vignali JD et al., J Xenobiot 2023 – safety of SARMs in healthy adults, systematic review
- Dahleh MMM et al., J Steroid Biochem Mol Biol 2023 – YK11, oxidative stress and mitochondria in the rat hippocampus
- Dahleh MMM et al., Chem Biol Interact 2024 – YK11 and hippocampal function in the rat
- German Anti-Doping Act (AntiDopG), annex to § 2 (3) – YK-11 listed by name
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Information only, not medical advice and not a usage or dosage recommendation. Prescription-only and unapproved substances belong in the hands of a physician. Last updated: 2026-10-05.