WARNING: LONG-TERM USE OF THIS MEDICINE INCREASES THE RISK OF DEVELOPING CERTAIN TYPES OF CANCERS (eg, leukemia, lymphoma, skin cancer). A rare type of cancer called hepatosplenic T-cell lymphoma (HSTCL) has been reported in patients treated with this medicine. These cases have been fatal. Most of these cases occurred in teenagers and young adults who had Crohn disease or ulcerative colitis. Some patients who developed this cancer were using this medicine along with certain other medicines called TNF blockers (eg, infliximab). Tell your doctor if you have or ever had any type of cancer. This medicine may also cause serious blood disorders (eg, anemias, low white blood cell or platelet levels). Discuss any questions or concerns with your doctor. CONTACT YOUR DOCTOR AT ONCE if you develop changes in the appearance or size of a mole; easy bruising or bleeding; unusual growths; unusual lumps or swelling (eg, in your neck, armpit, or groin); persistent unexplained itching; night sweats; signs of infection (eg, fever, chills, persistent sore throat); stomach pain or tenderness; unusual tiredness or weakness; or unexplained weight loss. Some medicines or medical conditions may interact with this medicine. INFORM YOUR DOCTOR OR PHARMACIST of all prescription and over-the-counter medicine that you are taking. DO NOT TAKE THIS MEDICINE if you are taking febuxostat or mercaptopurine. DO NOT TAKE THIS MEDICINE if you have rheumatoid arthritis and have taken alkylating agents (eg, cyclophosphamide, chlorambucil, melphalan) in the past. ADDITIONAL MONITORING OF YOUR DOSE OR CONDITION may be needed if you are taking alkylating agents (eg, cyclophosphamide, chlorambucil, melphalan), allopurinol, aminosalicylates (eg, mesalazine, olsalazine, sulfasalazine), angiotensin-converting enzyme (ACE) inhibitors (eg, enalapril, lisinopril), anticoagulants (eg, warfarin), disease-modifying antirheumatic drugs (DMARDs) (eg, methotrexate, adalimumab), doxorubicin, ribavirin, TNF blockers (eg, certolizumab, etanercept), or trimethoprim/sulfamethoxazole . DO NOT START OR STOP any medicine without doctor or pharmacist approval. Inform your doctor of any other medical conditions, including an infection, kidney or liver problems, certain bowel problems (eg, Crohn disease, ulcerative colitis), certain enzyme deficiencies (thiopurine methyltransferase / TPMT, xanthine oxidase), allergies, pregnancy, or breast-feeding. Tell your doctor if you have a history of frequent, recurrent, or prolonged infections; cancer; bone marrow problems; anemia; low white blood cell or platelet levels; or unusual bruising or bleeding. Tell your doctor if you have recently had a blood transfusion or if you have recently had or are scheduled to receive a vaccination. Contact your doctor or pharmacist if you have any questions or concerns about taking this medicine.