Mercaptopurine (also called 6-Mercaptopurine, 6-MP or its brand name Purinethol®) is an immunosuppressive drug used to treat leukemia. It is also used for pediatric non-Hodgkin's lymphoma, polycythemia vera, and psoriatic arthritis. It may also be used to treat inflammatory bowel disease (such as Crohn's Disease and ulcerative colitis).