YK-11 is an investigational synthetic compound commonly described as a selective androgen receptor modulator with additional interest surrounding myostatin-related pathways. Research remains limited, with much of the available evidence being preclinical or mechanistic. It is not an approved human therapeutic medicine or established fitness treatment. Potential concerns include hormonal suppression, liver effects, unfavorable lipid changes, cardiovascular complications, and reproductive disturbances. Its long-term safety, efficacy, and clinical significance remain insufficiently established.