(-)-Thalidomide is an immunomodulatory agent primarily used in the treatment of multiple myeloma, a type of blood cancer, where it inhibits angiogenesis, modulates the immune response, and promotes cancer cell death, often in combination with other therapies. It is also approved for managing erythema nodosum leprosum (ENL), a painful inflammatory complication of leprosy, by reducing inflammation and controlling abnormal immune reactions. Additionally, it has been employed in refractory cases of certain autoimmune diseases, such as lupus and rheumatoid arthritis, to suppress excessive immune activity. Thalidomide is not typically used to prevent organ transplant rejection. Due to its potent teratogenic effects, which can cause severe birth defects, it requires strict risk management programs, including contraception for users, and careful monitoring for other side effects like neuropathy and thrombosis.