YK-11 — Safety, Research, Risks & Legal Status

Not medical advice. YK-11 is discussed here for informational and harm-reduction purposes only. We do not endorse use, and any dosing context is informational, not a protocol.

Also known as	YK11
Category	SARM
steroidal_structure	Contains a steroid skeleton unlike true nonsteroidal SARMs
in_vitro_only	All published evidence derives from laboratory cell culture, no animal or human studies
myostatin_pathway	Proposed mechanism involves myostatin inhibition, setting it apart from classical androgen-receptor modulators
US legal status	YK-11 is not approved by the FDA for any use, and it is illegal to market or sell it as a dietary supplement. The FDA has warned that SARMs are associated with serious risks including liver injury, heart attack, and stroke, and products are sold as research chemicals not for human consumption. It is prohibited at all times in sport under the WADA list.

What is YK-11?

YK-11 is a synthetic compound often marketed as a SARM, though it is structurally a steroidal molecule that may act partly through myostatin-related pathways. It has been studied only in laboratory cell models.

How it works

YK-11 is a synthetic steroidal compound with a structure resembling anabolic steroids more than nonsteroidal SARMs. It activates the androgen receptor but may also act through non-receptor-mediated pathways, possibly including myostatin and follistatin signaling. The mechanism remains poorly characterized because studies are limited to cell culture.

Background & history

YK-11 was synthesized and studied in vitro by Japanese researchers at Toyo University in the 2000s as a potential myostatin inhibitor and muscle-building compound. No clinical development followed and no human trials were conducted. The compound entered underground markets and supplement channels without any regulatory oversight or further scientific investigation.

What the research says

Research suggests YK-11 promotes muscle-cell growth in laboratory studies and may influence myostatin signaling. There are essentially no human studies, so claims about its effects and safety in people are unsupported by clinical evidence.

Reported effects

Reported muscle-cell growth in laboratory studies
Studied effects on follistatin and myostatin pathways in cell models
Reported strength and muscle gains by users
Studied as a steroidal androgen-receptor modulator in vitro
Reported increases in power output in some user communities
Studied effects on myogenic differentiation in cell culture

Dosing & administration (informational)

No human pharmacokinetic or dose-finding studies exist. Claims of human dosing derive entirely from user communities and have no scientific basis. The steroidal structure suggests it may be metabolized like oral anabolic steroids, but this is speculation without supporting evidence.

This is general research/context information, not medical advice or a recommended protocol.

Safety & side effects

Reported to suppress natural testosterone production
Its steroidal structure raises concern for liver strain, though human data are absent
Can plausibly affect cholesterol and cardiovascular risk markers like other androgenic compounds
Has essentially no human safety data, making its risks largely unknown
Prohibited at all times in sport under the WADA list
Steroidal structure may confer greater hepatotoxicity risk than true nonsteroidal SARMs

Drug & supplement interactions

Likely to interact with hepatic metabolizing enzymes given steroidal structure, affecting many drugs
Strong potential for additive liver stress if combined with other hepatotoxic compounds
May amplify hormonal suppression if stacked with other androgenic compounds
Possible interactions with anticoagulants given plausible effects on clotting factors
Unknown interactions with virtually all drugs given complete lack of pharmacokinetic data

Who should avoid it

Avoid entirely given the absence of human safety data and steroidal hepatotoxicity concerns
Avoid in anyone with liver disease, elevated liver enzymes, or prior hepatotoxicity
Avoid concurrent use with other SARMs, anabolic steroids, or androgenic compounds
Avoid if at high cardiovascular or cancer risk
Avoid if subject to drug testing in sport or other regulatory contexts

How it is commonly combined

YK-11 is marketed for stacking with other compounds, but such use is entirely experimental and unjustifiable given the complete absence of human safety data. Stacking multiplies unknown hepatotoxic and hormonal risks without any evidence of benefit or safety.

Legal & regulatory. YK-11 is not approved by the FDA for any use, and it is illegal to market or sell it as a dietary supplement. The FDA has warned that SARMs are associated with serious risks including liver injury, heart attack, and stroke, and products are sold as research chemicals not for human consumption. It is prohibited at all times in sport under the WADA list.

Quality & harm reduction

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Lab testing & harm-reduction tools

If you are going to research a compound, verifying identity and purity is the single most protective step. Independent analytical testing and sterile-handling supplies reduce risk.

Compare testing options

Frequently asked questions

Is YK-11 a SARM or a steroid?

It is marketed as a SARM but is structurally steroidal and may act partly through myostatin-related pathways; the labeling is more marketing than precise classification.

What dose is safe?

We do not provide human dosing guidance. YK-11 has essentially no human data and any use should involve a qualified clinician.

Is YK-11 studied in humans?

No. Evidence is limited to laboratory cell studies, so human effects and safety are unknown.

Why is YK-11 steroidal if it is a SARM?

Its chemical structure is steroidal, unlike true SARMs, which is why classification is misleading. The steroidal backbone may confer greater hepatotoxicity risk.

Has YK-11 been tested for safety?

Only in cell culture. No animal toxicology or human studies have been published, making it purely experimental.

References & further reading

PubMed: YK-11 myostatin follistatin androgen receptor cell culture
PubMed: steroidal SARM YK11 muscle growth in vitro
FDA warning on SARMs and unapproved muscle-building compounds
WADA Prohibited List: YK-11 and synthetic androgenic agents
Toyo University Japanese pharmaceutical research myostatin inhibitors