RESEARCH MONOGRAPH · KDC-MN-267

YK-11

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 2 min read

Our opinion on this compound

38/100

Steroidal SARM-like compound with myostatin-related claims that the molecular data doesnt fully support

YK-11 is one of the more chemically unusual compounds in this batch. Synthesized at the Kanda lab in Tokyo and described in a 2011 paper, it's a steroidal molecule with a 17-alpha gem-dimethyl modification and a 4,5-cyclopropane ring fusion that distinguishes it structurally from both the testosterone series and the non-steroidal SARMs. The original work described it as a partial AR agonist with selective effects on muscle differentiation in C2C12 cells.

The myostatin angle is where the consumer narrative ran past the data. The 2013 follow-up paper from the same group reported that YK-11 increased follistatin expression in differentiating myoblasts, and the consumer interpretation became YK-11 inhibits myostatin. That isnt quite what the data shows. Follistatin can bind and sequester myostatin extracellularly, but the magnitude and clinical relevance of cell-line-level follistatin induction in vivo is not well-established. The compound has not been shown in any in vivo model to produce the kind of myostatin-knockout-mimetic effect the marketing implies.

The structural class also matters. YK-11 is steroidal, which means the hepatotoxicity considerations that apply to alkylated steroids partially apply here. The 17-alpha modifications in this scaffold arent identical to the methyl modifications in classic oral anabolics, but the structural similarity is enough that the hepatic concerns shouldnt be dismissed.

What we like, in narrow research-tool terms, is that YK-11 is a useful chemical probe for studying SARM-like activity in steroidal scaffolds, and the follistatin-induction observation is interesting basic cell biology even if it's been oversold for consumer use. The compound shows up in some interesting AR-coactivator-recruitment assays.

What we dont like is essentially everything about the consumer framing. There is no controlled human data on YK-11. None. Animal data is limited and mostly mechanism-of-action focused, not efficacy or safety. The hepatotoxicity case reports in the literature are sparse but the signal is consistent with what you'd expect for the structural class.

Sourcing is gray-market dominant and the compound's relative obscurity compared to ostarine or LGD-4033 has made counterfeit and mislabeling concerns less well-characterized. Research-grade material is available but verification is critical.

Honest take: structurally interesting, mechanistically interesting, clinically uncharacterized, oversold as a myostatin tool. The signal is mostly in vitro.

Evidence: 25
Mechanism: 55
Reliability: 40
Safety: 35
Sourcing: 40
Value: 35
Signal: 45
Staying power: 30

Plain-language summary Intrigue 50 / 100

YK-11 is an unusual SARM developed in Japan that, unlike most SARMs, retains a steroid-like backbone (modified androstane). In cell-culture studies it acts as a partial androgen receptor agonist and was reported to induce follistatin, a protein that blocks myostatin (the muscle-growth brake). The combination, in theory, would drive both androgen-receptor and myostatin-pathway muscle growth. The follistatin data come almost entirely from a single Japanese laboratory and have not been independently replicated in vivo. There are no human trials, no pharmacokinetic data, and persistent reports of liver-enzyme elevation in users. Treat the muscle-growth claims as hypothesis, not established fact. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

SARM with myostatin-related activity

A non-steroidal SARM with reported follistatin-inducing and myostatin-modulating activity beyond AR agonism.

Abstract

YK-11 (17-alpha,20E-(((((4-methoxyphenyl)sulfonyl)methylene)-bisoxy))-17-beta-(methoxycarbonyl)methyl-androst-1,4-dien-3-one; molecular formula C25H34O6; molecular weight 430.54) is a structurally novel SARM developed in Japan and described initially by the Yale-Kanno group at Toho University. Distinct from aryl propionamide SARMs by retaining a steroidal scaffold (modified androstane); the compound was reported as a tissue-selective AR partial agonist with concurrent induction of follistatin in C2C12 myoblast cultures, theoretically producing additive muscle hypertrophy through myostatin pathway inhibition. The follistatin-inducing claim is supported by a single research group and has not been independently replicated. No clinical trials. The compound is widely used recreationally as a high-potency SARM-class agent. Plasma half-life and pharmacokinetic data are sparse.

Mechanism of action

Steroidal SARM scaffold with reported follistatin induction and consequent myostatin pathway inhibition. Independent replication limited.

Reported research dose ranges

Recreational use commonly 5 to 10 mg in the published literature; no clinical trial data.

References

Kanno Y, et al. (17-alpha,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxo-19-norpregna-4,20-diene-21-carboxylic acid methyl ester (YK-11) is a partial agonist of the androgen receptor. Biol Pharm Bull 2011.
Kanno Y, et al. YK11 induces myogenic differentiation through follistatin in C2C12 cells. Biochem Biophys Res Commun 2013.
Solomon ZJ, et al. Selective androgen receptor modulators: current knowledge and clinical applications. Sex Med Rev 2019.

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KDC-MN-267

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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YK-11

Abstract

Mechanism of action

Reported research dose ranges

References

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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