Mycophenolic acid is an immunosuppresant most often used in transplant patients to prevent rejection. It works by blocking an enzyme needed in the growth of B cells and T cells. It can also be used in place of steroids for some autoimmune conditions.
Its most common side effects are diarrhea, nausea, joint pain, infection and damage to red blood cells and white blood cells leading to anemia and leukopenia. It is also far more expensive than treatment with alternative drugs.