YK-11

A steroidal compound structurally derived from dihydrotestosterone (DHT) that exhibits a dual mechanism: partial agonism at the androgen receptor (SARM-like activity) combined with myostatin inhibition through increased follistatin expression. While often classified with SARMs, its steroidal backbone and unique follistatin-inducing properties place it in a distinct pharmacological category. It is technically a gene-selective androgen receptor modulator with anti-myostatin activity.

• Partial agonist at the androgen receptor, inducing selective gene transcription in muscle tissue
• Increases expression of follistatin in C2C12 myoblasts, indirectly inhibiting myostatin
• Steroidal backbone (19-nor DHT derivative) provides androgen receptor binding affinity
• Does not appear to induce full AR conformational change, leading to gene-selective effects
• Downstream Akt phosphorylation promotes anabolic signaling in skeletal muscle

• Pre-existing liver disease or elevated liver enzymes
• Women of childbearing potential (steroidal compound)
• Adolescents or those with open growth plates
• History of hormone-sensitive cancers
• Concurrent use of hepatotoxic medications

Store oral formulations at room temperature (15–25°C (59–77°F)) in a cool, dry place away from light. Injectable preparations: store at 2–8°C (36–46°F).

YK-11 was first described by Kanno et al. (2011) in a study on C2C12 myoblast cells, demonstrating that it induced myogenic differentiation and increased follistatin expression more effectively than DHT. Subsequent in vitro studies confirmed its dual AR-agonist and myostatin-inhibiting activity. No in vivo animal or human clinical trials have been published. Its classification remains debated — it shares features with both SARMs and anabolic steroids. Extreme caution is warranted due to the complete absence of clinical safety data.