YK-11 — research, mechanism and SARM status

A chemical reagent intended exclusively for laboratory research (Research Use Only). It is not a medicinal product, a dietary supplement, or a food product. It is not intended for administration to humans or animals outside a controlled experimental environment.

YK-11 occupies a special position within the family of androgen receptor modulators. On one hand, it attracts interest because of its steroidal scaffold and the “anti-myostatin pathway” described in vitro. On the other — it is the compound about which the least is known of the entire group. This article sorts out what has actually been demonstrated in peer-reviewed studies and what remains purely a hypothesis. All available knowledge comes from cell cultures.

Educational note. The following text is a review of the scientific literature concerning a research reagent. It does not constitute health advice, dietary advice, or an encouragement to use it. YK-11 is not intended for human consumption. All the described observations come from in vitro studies and have not been confirmed in a living organism.

What YK-11 is and where it comes from

YK-11 was characterized by the team of Yuichiro Kanno and colleagues at the turn of the second decade of the 21st century. In the first paper (Kanno et al., 2011) it was described as a compound with a steroidal scaffold — a 19-norpregnadiene derivative — and classified as a partial agonist of the androgen receptor (AR).

This dual nature explains the nomenclatural confusion surrounding the compound. Structurally, YK-11 is a synthetic steroid, which a later paper confirmed outright, referring to the “synthetic steroid YK11” (Kanno et al., 2022). Functionally, however, it behaves like a selective AR modulator, activating the receptor differently than full androgens. This is why the term “steroidal SARM” appears in the literature. It is worth understanding this distinction: the chemical scaffold is steroidal, whereas the receptor-action profile is closer to the logic of selective modulators.

The historical context is also important. YK-11 entered scientific circulation relatively late compared with the first wave of non-steroidal AR modulators, and its characterization was from the outset conducted in a narrow set of cell models by a single research center. This distinguishes it from compounds that entered broader preclinical and clinical programs carried out by different teams. In practice, this means that the picture of YK-11 rests on a coherent but limited number of publications, without independent verification at the organism level.

Mechanism — partial AR agonism and the follistatin/myostatin pathway

The core of YK-11’s mechanism was described in two papers by the Kanno team.

The first (Kanno et al., 2011) established that YK-11 is a partial agonist of the androgen receptor. This means that it binds the receptor but activates it in a limited manner, different from full agonists, leading to a different pattern of gene expression.

The second and most frequently cited paper (Kanno et al., 2013) concerns C2C12 myoblasts. In these cells, YK-11 increased the expression of follistatin and induced markers of myogenic differentiation. Follistatin is a protein that binds and antagonizes myostatin — a factor that inhibits the growth of muscle tissue. It is precisely on this observation that the entire market narrative about YK-11’s “anti-myostatin potential” rests.

A clear caveat is needed here. An increase in follistatin expression in a culture dish with myoblasts is a molecular phenomenon in isolated cells. It is not evidence of an increase in muscle mass in a living organism, because such a study has never been conducted — neither in animals nor in humans. The follistatin/myostatin mechanism for YK-11 remains a cellular observation, not a physiological effect.

YK-11 in research — cell cultures only

The full set of peer-reviewed observations on YK-11 fits within a few in vitro models:

• C2C12 myoblasts. An increase in the expression of follistatin and of markers of myogenic differentiation (Kanno et al., 2013). This is the compound’s most important mechanistic observation.
• MC3T3-E1 osteoblasts. An effect on the proliferation and differentiation of bone cells was reported (Yatsu et al., 2018). This paper extends interest in YK-11 beyond muscle tissue to a bone model — also exclusively at the cellular level.
• MDA-MB-453 breast cancer cells. The molecular basis of its action was studied: differences in DNA binding and in the recruitment of cofactors by the androgen receptor (Kanno et al., 2022). This paper explains why the “synthetic steroid YK11” shapes gene expression differently than classical androgens.

Note the common denominator of all three models — they are cell lines cultured under laboratory conditions. None of the described results comes from a living organism.

It is also worth noting what is missing from this list. There are no studies on isolated animal tissues, no rodent models assessing muscle mass or bone density, no measurements of how the compound behaves after absorption. The classical pathway for characterizing a compound comprises, in sequence, in vitro studies, then animal models, and only then human studies. YK-11 has stopped at the first of these stages. In its case, any transfer of a conclusion from cell culture to a higher level of biological organization remains speculation, not a documented fact.

YK-11 and the lack of human data — the least characterized SARM

This is a section that cannot be omitted in an honest description of YK-11. For this compound there are no studies in humans or in animal models. No phase I, II, or III trials have been published. There are no human pharmacokinetic data, no described safety profile, no descriptions of adverse effects from controlled studies. All knowledge of YK-11 ends at the level of cell culture.

This has two consequences. First, in vitro results do not automatically translate to a living organism. A single cell line in a dish does not reproduce absorption, hepatic metabolism, tissue distribution, excretion, or systemic interactions. A cell’s response in culture is a starting point for further research, not its culmination. Second, the very absence of any human safety data is an independent signal for caution — everything remains unknown, from the toxicity threshold to the long-term consequences.

A critical review of AR modulators (Bond et al., 2025) places YK-11 among the compounds with the weakest evidence base and points to the limitations of the entire class. In a broader context, it is worth remembering that adverse events have been described for the SARM group, including signals concerning the liver and hormonal balance (Leciejewska et al., 2024) — although these data concern the class and not YK-11 itself, for which such observations in humans have simply not been collected.

For those conducting research, a clear methodological conclusion follows from this. YK-11 should be treated as a starting point for further characterization, not as a compound with an established action profile. An interesting molecular signal in culture — such as the effect on follistatin expression — is a valuable premise for designing subsequent experiments, but it does not justify any claims about action in the human body. In the subject literature, it is precisely this interpretive caution that distinguishes a reliable description from marketing extrapolation.

YK-11 and its WADA and legal status

YK-11 is offered exclusively as a laboratory research reagent (RUO). It has no registration as a medicinal product — there is no authorization from the EMA or from any other body approving it for marketing as a drug or supplement.

In sport, the compound is a prohibited substance in category S1 (anabolic agents) according to the World Anti-Doping Agency (WADA). Anti-doping methods detect YK-11 and its metabolites in samples, which makes it an unambiguously prohibited substance for athletes subject to testing.

YK-11 vs ostarine — a gulf in the evidence base

Comparing YK-11 with ostarine (MK-2866) clearly illustrates how wide the spread is within the family of AR modulators itself. Ostarine is the best-studied compound of the group, with phase III clinical trials in patients. YK-11 sits at the opposite extreme — its evidence ends at cell cultures. We expand on this juxtaposition of the two extremes of the evidence spectrum in a separate article: YK-11 vs ostarine — what the research says, and you will find the broader context of the entire class in the guide to SARMs.

FAQ

Is YK-11 a steroid or a SARM?

Structurally it is a synthetic steroid (a 19-norpregnadiene scaffold), functionally — a partial agonist of the androgen receptor. Hence the term “steroidal SARM” (Kanno et al., 2011; 2022).

Are there human studies of YK-11?

No. There are no studies in humans or in animal models. The evidence base is exclusively cell cultures.

What does the YK-11 “myostatin pathway” mean?

In C2C12 myoblasts, YK-11 increased the expression of follistatin, which antagonizes myostatin (Kanno et al., 2013). This is a cellular observation, not an effect demonstrated in a living organism.

Why is YK-11 said to be poorly understood?

Because the entire body of work is a handful of in vitro papers, with no data from a living organism and no human safety profile (Bond et al., 2025).

Is YK-11 detectable in anti-doping testing?

Yes. YK-11 belongs to WADA category S1, and analyses detect the compound and its metabolites.

Summary

• YK-11 is a synthetic compound with a steroidal scaffold, described as a partial agonist of the androgen receptor (Kanno et al., 2011).
• The most important mechanistic observation — an increase in follistatin expression in C2C12 myoblasts — comes from cell culture (Kanno et al., 2013).
• Additional in vitro models: MC3T3-E1 osteoblasts (Yatsu et al., 2018) and MDA-MB-453 cells (Kanno et al., 2022).
• No studies whatsoever in humans or animals; the cellular results do not translate to a living organism — YK-11 is the least characterized compound of the group (Bond et al., 2025).
• Status: RUO reagent, no EMA registration; WADA category S1, detectable in anti-doping testing.

Related reagents: YK-11 — reagent card and YK-11 category.

Scientific sources

1. Kanno Y et al. (2011). (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
2. Kanno Y et al. (2013). Selective androgen receptor modulator, YK11, regulates myogenic differentiation of C2C12 myoblasts by follistatin expression
3. Yatsu T et al. (2018). Selective Androgen Receptor Modulator, YK11, Up-Regulates Osteoblastic Proliferation and Differentiation in MC3T3-E1 Cells
4. Kanno Y et al. (2022). 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
5. Leciejewska N et al. (2024). Selective androgen receptor modulator use and related adverse events
6. Bond P et al. (2025). Selective androgen receptor modulators: a critical appraisal

Bartosz BartczakPhysiotherapist, Personal Trainer

Physiotherapist with 20 years of clinical experience, graduate of Poznan University of Medical Sciences. Founder of One Peptides and lead author of clinical-perspective content.

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