The Development History of YK-11: Why the Compound Never Reached Pharmacies

YK-11 differs from the rest of the compounds sold as SARMs in one respect: it has no corporate development history. There was no pharmaceutical company, no trial program, no application to a regulator. There was a series of laboratory publications — and suddenly a mass market. Our editorial team reconstructed the timeline and explains why it is incorrect to call YK-11 a “drug.”

Academic origin, not a pharmaceutical project

Most well-known androgen receptor modulators appeared within pharmaceutical programs: ostarine (enobosarm) was developed by GTx, LGD-4033 by Ligand Pharmaceuticals, and andarine comes from the same academic-corporate line of the University of Tennessee and GTx. Each of them has a clinical trial number, protocols, and safety reports.

YK-11 arose differently. It was described in the work of Japanese researchers (Kanno and colleagues) around 2011 as the result of a chemical search for compounds with partial activity at the androgen receptor. This was academic pharmacology: cell lines, analysis of transcriptional activity, measurement of gene expression. No application to develop a medicinal product was filed based on these publications.

Because of this, YK-11 never had what even compounds with interrupted development have: data on pharmacokinetics in humans, toxicity studies to regulatory standards, or established tolerability. The compound exists in the scientific literature as a chemical tool, and in commerce — as a product.

The gap between these two states is the key to understanding the whole story. A publication in a scientific journal means that a substance did something interesting in a test tube. It does not mean that the substance was studied from the standpoint of human safety — and in the case of YK-11 it did not.

Why it is called a “myostatin SARM”

The loudest marketing claim is that YK-11 suppresses myostatin, a protein that limits muscle growth. The basis for this was the work of Kano and colleagues, in which, in a line of mouse C2C12 myoblasts, an increase in the expression of follistatin — a natural antagonist of myostatin — was observed under the action of YK-11, more strongly than under the action of dihydrotestosterone.

This is a real experimental result, but it is important to see its limits. It concerns a cell culture, not an organism; follistatin, not the direct blocking of myostatin; a relative comparison with another androgen, not an absolute magnitude of effect. Whether this leads to an increase in muscle mass in humans has not been studied.

The pharmacology itself also implies a nuance that advertising usually keeps quiet about: YK-11 has a steroidal structure. It is a derivative of dihydrotestosterone with additional functional groups, not a non-steroidal compound like andarine or ostarine. So calling it a “SARM” in the same sense as non-steroidal modulators is chemically inaccurate.

Next comes the nature of its action. In publications YK-11 was described as a partial agonist of the androgen receptor: it does not activate all pathways of the receptor signal equally. For a pharmacologist this means a complex and context-dependent effect that cannot be predicted from a single cell experiment.

How the compound reached the market without development

The mechanism is simple and repeatable. The chemical structure is published in open access, the synthesis is technically uncomplicated for contract laboratories, and the sale is framed as a “reagent for scientific research.” This formula makes it possible to claim neither the status of a medicine nor the status of a dietary supplement — and thus to bypass the corresponding requirements.

Next, marketing in niche communities does its work: the more exotic the mechanism, the more attractive the story. “Suppresses myostatin” sounded stronger than “activates the androgen receptor,” so YK-11 quickly acquired the reputation of the “most powerful SARM” — without any comparative studies to confirm it.

Regulators reacted only after the fact. The FDA repeatedly warned consumers about the dangers of products containing SARMs and sent letters to the companies selling them. Anti-doping organizations included compounds of this class in the WADA Prohibited List (category S1), and YK-11 falls under this category.

Another side of the market is the actual content. A study by Van Wagoner and colleagues (2017) showed that in about half of the tested products sold as SARMs, the composition did not match the labeling. For a compound that no one has studied in humans, this means double uncertainty: an unknown substance in an unknown amount.

What science managed to record after it appeared on the market

Since there were no clinical trials, the main source of data on YK-11 in humans is clinical reports of adverse events. The literature describes cases of drug-induced liver injury associated with products of the SARM class, in particular with YK-11 (the review by Leciejewska et al., 2024, analyzes such reports).

Additionally, analytical works appeared: anti-doping laboratories described the metabolites and methods for detecting the compound in urine. These studies are important for control, but say nothing about safety — they answer only the question of whether the fact of use can be established.

Several laboratory works continued to study the mechanism. In particular, researchers described the effect of YK-11 on bone tissue cells and on signaling pathways in myoblasts. This deepens the understanding of molecular biology, but remains at the cellular level.

Thus, over more than ten years the compound has still not received a single study in humans that would evaluate efficacy or tolerability. All we have are cellular experiments and reports of harm.

Why it “never reached pharmacies” — and will not

Formally the answer is simple: to reach a pharmacy, a substance must pass preclinical toxicology, three phases of clinical trials, and registration. YK-11 never began this path. But the more interesting question is why no one took it up, despite its commercial popularity.

First, registration requires a medical indication. The market for drugs against muscle-mass loss is complex: even enobosarm, which reached large trials, did not obtain registration for the indication of cancer cachexia because it did not meet all the endpoints. Investing in a compound with no clinical data is even riskier.

Second, YK-11 is a steroidal molecule with partial agonist activity, that is, without the marketing advantage of “non-steroidal” status that the pharmaceutical programs operated on. For a regulator this is more of a complication than an advantage.

Third, the substance is already in free illegal circulation and is banned in sport. A company that decided to develop it would start with reputational and legal baggage, and the patent situation after the open publication of the structure also does not favor investment.

• No clinical data— and without them registration is impossible in principle.
• No indicationwith proven benefit for which it would be submitted.
• There is a “reagent” marketthat requires no studies at all.
• There is a WADA banand regulators’ warnings about products of this class.

The story of YK-11 clearly illustrates a general pattern: in the modern circulation of “research compounds,” popularity is determined not by evidence but by the appeal of a scientific legend. Readers interested in this topic are also recommended our materials “YK-11: What This Substance (SARM) Is and How It Works,” “Side Effects of YK-11,” and “Myths About YK-11.”

Editorial conclusions

YK-11 was never a pharmaceutical project: it appeared in academic publications as a chemical tool and from there went straight into commercial circulation.

The claim about myostatin suppression rests on a cell culture experiment and concerns an increase in follistatin, not the direct blocking of myostatin in the body.

Chemically it is a steroidal compound, so the term “SARM” is used inaccurately for it, and its nature as a partial agonist makes its effects difficult to predict.

Over more than ten years not a single clinical trial has appeared, but reports of liver injury have. This is the practical bottom line of the story.

References

1. Kanno Y, Ota R, Someya K, et al. Selective androgen receptor modulator, YK11, regulates myogenic differentiation of C2C12 myoblasts by follistatin expression. Biol Pharm Bull. 2013;36(9):1460–1465.
2. Kanno Y, Hikosaka R, Zhang SY, et al. (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. Biol Pharm Bull. 2011;34(3):318–323.
3. Solomon ZJ, Mirabal JR, Mazur DJ, et al. Selective androgen receptor modulators: current knowledge and clinical applications. Sex Med Rev. 2019;7(1):84–94.
4. Leciejewska N, Jędrejko K, Gómez-Renaud VM, et al. Selective androgen receptor modulator use and related adverse events including drug-induced liver injury. Eur J Clin Pharmacol. 2024;80(2):185–202.
5. Van Wagoner RM, Eichner A, Bhasin S, 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.
6. Dalton JT, Barnette KG, Bohl CE, et al. The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women. J Cachexia Sarcopenia Muscle. 2011;2(3):153–161.
7. World Anti-Doping Agency. Prohibited List. Montreal: WADA; чинна редакція.