(R)-()-Thalidomide is primarily used in the treatment of multiple myeloma, a type of blood cancer. It works by inhibiting the growth of cancer cells and reducing the formation of new blood vessels that supply tumors, a process known as angiogenesis. Additionally, it is employed in managing erythema nodosum leprosum, a painful inflammatory complication of leprosy, by modulating the immune response and reducing inflammation. Due to its immunomodulatory and anti-inflammatory properties, it is also being investigated for potential use in other conditions such as Crohn's disease, rheumatoid arthritis, and certain autoimmune disorders. However, its use is strictly regulated due to its teratogenic effects, which can cause severe birth defects if taken during pregnancy.