What side effects are possible with this medication?

A side effect is an unwanted response to a medication when it is taken in normal doses. A side effect may be mild or severe, temporary or permanent, but does not occur in everyone. Not everyone will experience side effects, and which side effects a person experiences cannot be anticipated.

The following side effects have been reported by at least 1% of people taking this medication. If you develop any of these side effects (or any other side effects not listed here) or they change in intensity, speak to your doctor or pharmacist for advice on managing them and on the risks and benefits of the medication.

• appetite loss
• cough or hoarseness
• darkening of skin
• diarrhea
• fever or chills
• nausea and vomiting
• pinpoint red spots on skin
• skin rash and itching
• sores in mouth or on lips
• temporary loss of hair
• unusual tiredness or weakness

Click here to learn about serious side effects that can potentially occur with any medication. These examples are provided for information purposes only and are not meant to be exhaustive. Always consult your doctor for sound medical advice specific to your particular medication and treatment.

Are there any other precautions or warnings for this medication?

Be sure to inform your doctor of all your medical conditions before you begin taking a medication. Some conditions can affect how you should take this medication.

Blood clotting: This medication can reduce the number of platelet cells in the blood. Platelets help the blood to clot, and a shortage could make you bleed more easily. Seek immediate medical attention if you notice unusual or unexplained bleeding. Symptoms include easy bruising, bleeding gums, nosebleeds, spitting or vomiting blood (like ground coffee), brown or discolored urine, or bloody, black, or tarry stools.

Blood tests: Your doctor will recommend regular blood tests while you are taking this medication. Be sure to keep all appointments for blood tests, and let your doctor know if you miss an appointment.

Damage to cells: This medication can potentially cause cancer, birth defects, and temporary or permanent fertility problems. Talk to your doctor for more information.

Genetics: People with defects in their thioguanine-S-methyltransferase gene may be more sensitive to the side effects of this medication as compared to people who do not have this defect.

Infection: As well as killing cancer cells, this medication can reduce the number of cells that fight infection in the body (white blood cells). Avoid contact with people with contagious infections and tell your doctor if you begin to notice signs of an infection, such as fever or chills.

Kidney disease: People with kidney disease may require close monitoring and dosing adjustments of this medication.

Liver: This medication may cause damage to the liver. You may need to be closely monitored by your doctor while you are taking this medication, especially for the first few months. Contact your doctor as soon as possible if you develop symptoms of liver damage (symptoms include yellow skin or eyes, abdominal pain, dark urine, clay-colored stools, loss of appetite, or nausea and vomiting).

Pregnancy: There is a possibility of birth defects if either the man or woman is using mercaptopurine at the time of conception, or if it is taken during pregnancy. It may harm the baby if used during pregnancy. Effective birth control should be practiced while using this medication.This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: It is not known if mercaptopurine passes into breast milk. If you are a breast-feeding mother and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

What other drugs could interact with this medication?

An interaction between medications does not always mean that you must stop taking one of them. The following medications may affect the way mercaptopurine works, be affected by mercaptopurine, or increase the risk of side effects:

• allopurinol
• aminosalicylate derivatives (e.g., olsalazine, mesalazine, sulfasalazine)
• thioguanine
• trimethoprim or sulfamethoxazole
• warfarin
• other cancer medications

If you are taking any of these or other medications (including non-prescription, herbal, and supplement products), speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want to change your therapy or may suggest ways of managing any interactions. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your doctor know if you use them. Medications other than those listed above may also interact with this medication.