This medication is used to treat a certain type of cancer (acute lymphocytic leukemia). It is a chemotherapy drug that works by slowing or stopping the growth of cancer cells.

Talk to the doctor about the risks and benefits of mercaptopurine, especially when used by children and young adults.

This section contains uses of this drug that are not listed in the approved professional labeling for the drug but that may be prescribed by your health care professional. Use this drug for a condition that is listed in this section only if it has been so prescribed by your health care professional.

This drug may also be used for other types of leukemia or certain types of bowel conditions (Crohn's disease, ulcerative colitis).

Read the Patient Information Leaflet if available from your pharmacist before you start taking mercaptopurine and each time you get a refill. If you have any questions, ask your doctor or pharmacist.

Take this medication by mouth with or without food as directed by your doctor, usually once daily. Drink plenty of fluids while taking this medication unless otherwise directed by your doctor. Doing so may help decrease the risk of certain side effects (kidney problems).

If you are using the suspension, shake the bottle well for at least 30 seconds before each dose. Carefully measure the dose using the provided special measuring device. Do not use a household spoon because you may not get the correct dose. Avoid getting any of the suspension on your skin or in your eyes. If contact occurs, wash the affected skin area or rinse your eyes with water. Consult your pharmacist for details.

The dosage is based on your medical condition, weight, and response to treatment. Do not increase your dose or use this drug more often or for longer than prescribed. Your condition will not improve any faster, and your risk of serious side effects will increase.

Use this medication regularly to get the most benefit from it. To help you remember, take it at the same time each day.

Since this drug can be absorbed through the skin and lungs and may harm an unborn baby, women who are pregnant or who may become pregnant should not handle this medication or breathe the dust from the tablets.

Nausea, vomiting, diarrhea, and loss of appetite may occur. Temporary hair loss may also occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly.

People using this medication may have serious side effects. However, you have been prescribed this drug because your doctor has judged that the benefit to you is greater than the risk of side effects. Careful monitoring by your doctor may decrease your risk.

Tell your doctor right away if you have any serious side effects, including:

• joint pain/swelling
• black stools
• vomit that looks like coffee grounds
• signs of kidney problems (such as change in the amount of urine, pain in the lower back/side)

Get medical help right away if you have any very serious side effects, including:

• symptoms of liver disease (such as nausea/vomiting that doesn't stop, stomach/abdominal pain, yellowing eyes/skin, dark urine)

This medication may decrease bone marrow function, an effect that may lead to a low number of blood cells such as red cells, white cells, and platelets. This effect can cause anemia, decrease your body's ability to fight an infection, or cause easy bruising/bleeding. Tell your doctor right away if you develop any of the following symptoms:

• unusual tiredness
• pale skin
• signs of infection (such as sore throat that doesn't go away, fever, chills)
• easy bruising/bleeding

Mercaptopurine may rarely increase your risk of developing certain types of cancer (such as lymphoma, skin, cervical). This risk is higher in children/young adults being treated for certain bowel diseases (such as Crohn's disease, ulcerative colitis). Tell your doctor right away if you develop any of the following symptoms:

• swollen abdomen
• swollen lymph nodes
• night sweats
• unexplained weight loss
• unusual skin changes (such as new skin lesion or bump, or change in size or color of a mole)
• unusual vaginal bleeding/discharge

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including:

• rash
• itching/swelling (especially of the face/tongue/throat)
• dizziness
• trouble breathing

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Before taking mercaptopurine, tell your doctor or pharmacist if you are allergic to it; or to azathioprine; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of:

• kidney disease
• liver disease
• cancer
• certain enzyme disorders (TPMT deficiency, NUDT15 deficiency)

Mercaptopurine can make you more likely to get infections or may make current infections worse. Stay away from anyone who has an infection that may easily spread (such as chickenpox, COVID-19, measles, flu). Talk to your doctor if you have been exposed to an infection or for more details.

Tell your health care professional that you are using mercaptopurine before having any immunizations/vaccinations. Avoid contact with people who have recently received live vaccines (such as flu vaccine inhaled through the nose).

To lower the chance of getting cut, bruised, or injured, use caution with sharp objects like razors and nail cutters, and avoid activities such as contact sports.

This medication may make you more sensitive to the sun. Limit your time in the sun. Avoid tanning booths and sunlamps. Use sunscreen and wear protective clothing when outdoors. Tell your doctor right away if you get sunburned or have skin blisters/redness.

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

Since this drug can be absorbed through the skin and lungs and may harm an unborn baby, women who are pregnant or who may become pregnant should not handle this medication or breathe the dust from the tablets.

Tell your doctor if you are pregnant or plan to become pregnant. You should not become pregnant while using mercaptopurine. Mercaptopurine may harm an unborn baby, especially during the first 3 months of pregnancy. Your doctor should order a pregnancy test before you start this medication. Women using this medication should ask about reliable forms of birth control during treatment and for 6 months after the last dose. Men using this medication should ask about reliable forms of birth control during treatment and for 3 months after the last dose. If you or your partner becomes pregnant, talk to your doctor right away about the risks and benefits of this medication.

It is unknown if this drug passes into breast milk. Because of the possible risk to the infant, breastfeeding is not recommended while using this drug and for 1 week after the last dose. Consult your doctor before breastfeeding.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

Some products that may interact with this drug are:

• febuxostat
• other drugs that weaken the immune system/increase the risk of infection (such as rituximab, tofacitinib)

This medication may interfere with certain lab tests (such as uric acid levels), possibly causing false test results. Make sure lab personnel and all your doctors know you use this drug.

Mercaptopurine is very similar to azathioprine. Do not use medications containing azathioprine while using mercaptopurine.

If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call 1-800-222-1222. Canada residents can call 1-844-764-7669.

Do not share this medication with others.

Lab and/or medical tests (such as complete blood count, liver/kidney function) should be done while you are taking this medication. Keep all medical and lab appointments. Consult your doctor for more details.

If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose. Take your next dose at the regular time. Do not double the dose to catch up.

Store at room temperature away from light and moisture. Do not store in the bathroom. For the suspension form, once the bottle is opened, the medication expires after 8 weeks. Keep all medications away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company.

Your condition can cause complications in a medical emergency. For information about enrolling in MedicAlert, call 1-888-633-4298 (US) or 1-800-668-1507 (Canada).