LGD-4033, also known as Ligandrol, is an investigational selective androgen receptor modulator developed to study tissue-selective androgen activity. Research has investigated its effects on lean body mass and muscle-related physiology. It is not an approved human therapeutic medicine or established fitness treatment. Clinical evidence remains limited, while potential concerns include testosterone suppression, unfavorable lipid changes, liver effects, cardiovascular complications, and reproductive disturbances requiring further scientific evaluation.