YK-11
Also known as: (17α,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxo-19-norpregna-4,20-diene-21-carboxylic acid methyl ester, YK11, Myostine
Summary
YK-11 is a synthetic steroidal selective androgen receptor modulator (SARM) structurally derived from dihydrotestosterone that exhibits both androgen receptor agonist activity and myostatin inhibition properties. It uniquely induces muscle differentiation by upregulating follistatin expression, a potent myostatin antagonist, leading to enhanced anabolic effects in skeletal muscle and bone tissue. YK-11 remains an experimental compound with no FDA approval, limited to in vitro and animal studies, with concerning safety profiles including neurotoxicity, hepatotoxicity, testosterone suppression, and cardiovascular risks. The compound is banned by WADA for athletic use and is not approved for human consumption in any jurisdiction.
Potential Benefits
Muscle Growth and Myogenic Differentiation
YK-11 demonstrates potent anabolic effects by activating androgen receptors and inducing myogenic differentiation in skeletal muscle cells. In C2C12 myoblast studies, YK-11 significantly increased expression of key myogenic regulatory factors including MyoD, Myf5, and myogenin to a greater extent than dihydrotestosterone (DHT) [1]. The compound uniquely stimulates follistatin expression, which acts as a myostatin antagonist, promoting muscle hypertrophy and differentiation [1]. This dual mechanism of androgen receptor activation combined with myostatin inhibition suggests enhanced muscle-building potential compared to traditional androgens.
Bone Health and Osteoblast Activity
Research indicates YK-11 exhibits osteogenic properties by accelerating osteoblast proliferation and differentiation. In MC3T3-E1 mouse osteoblast cells, YK-11 treatment increased cell proliferation, mineralization, and expression of bone-specific markers including osteoprotegerin and osteocalcin [2]. The compound activates Akt signaling pathways through non-genomic androgen receptor mechanisms, suggesting potential therapeutic applications for bone mineral density enhancement [2].
Anti-Inflammatory Effects in Sepsis
Preclinical studies demonstrate YK-11's myostatin inhibition may provide protective effects during bacterial sepsis. In septic mouse models, YK-11 administration reduced pro-inflammatory cytokines, decreased organ damage markers, and lowered mortality rates [3]. The compound helped prevent sepsis-related muscle wasting by counteracting catabolic processes in skeletal muscle, suggesting potential therapeutic value in critical care settings [3].
IMPORTANT NOTE: All benefits are derived from cell-based and animal studies only. YK-11 has never been tested in human clinical trials, and its safety and efficacy in humans remain unproven [1][2][3][4].
Safety Information
Neurotoxicity and Cognitive Impairment
Recent studies reveal significant neurological safety concerns with YK-11 administration. Research demonstrates that YK-11 induces oxidative stress and mitochondrial dysfunction in the hippocampus, impairing memory consolidation and neurochemistry [4][5]. The compound promotes alterations in endogenous antioxidant systems and proteotoxic effects, with exercise providing only partial mitigation of these harmful neurological effects [5]. These findings suggest YK-11 may pose substantial risks to cognitive function and brain health, particularly concerning for athletes and bodybuilders.
Hepatotoxicity
YK-11's chemical structure includes modifications that raise serious liver toxicity concerns. As a 17-alpha alkylated compound with a methyl ester group, YK-11 exhibits hepatotoxic properties similar to oral anabolic steroids [6]. Prolonged use or high doses of 17-α-alkylated compounds are associated with liver carcinoma, cholestatic jaundice, and impaired hepatic excretion function [6]. Users commonly report elevated ALT and AST liver enzymes, particularly at dosages above 15 mg/day, though no formal human clinical safety data exists.
Testosterone Suppression and Endocrine Disruption
YK-11 causes marked suppression of endogenous testosterone production through disruption of the hypothalamus-pituitary-testicular axis, reducing luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion [6]. This suppression leads to various adverse effects including fatigue, reduced libido, hormonal imbalances, mood disturbances, and potential infertility [6]. Post-cycle therapy is necessary to restore normal hormonal function, though recovery timelines remain unstudied in clinical settings.
Cardiovascular Risks
Like other SARMs, YK-11 has been associated with increased blood pressure, decreased HDL cholesterol levels, and elevated cardiac stress markers in animal studies [6]. The FDA has warned that SARMs may increase the risk of heart attack and stroke, though specific human cardiovascular data for YK-11 is lacking [6]. The long-term impact on cardiovascular, renal, and reproductive systems remains speculative due to absence of human trials.
Regulatory and Legal Status
YK-11 is not approved by the FDA or any regulatory agency for human use and is classified as an unapproved experimental compound [6]. It is prohibited by the World Anti-Doping Agency (WADA) as a banned substance for athletic competition, with the first positive doping test reported in 2023 [7][8]. The compound is illegal to market as a dietary supplement and is typically sold as a "research chemical not for human consumption."
Cancer-Related Concerns
Some evidence suggests YK-11's follistatin-inducing properties may increase cancer risk, particularly for esophageal, gastric, skin, and prostate cancers, though human data is absent [6].