Used primarily as an immunosuppressant to prevent organ rejection in patients receiving kidney, heart, or liver transplants. It works by inhibiting the proliferation of T and B lymphocytes, which are key components of the immune response. Commonly prescribed in combination with other immunosuppressants like cyclosporine and corticosteroids. Also used in the treatment of autoimmune diseases such as lupus and psoriasis when other therapies are ineffective. Available in both oral and intravenous formulations for clinical use.