Skip to Main Content

Welcome to

Together is a new resource for anyone affected by pediatric cancer - patients and their parents, family members, and friends.

Learn More



Brand names:

Purixan®, Purinethol®

Other names:


Often used for:

Leukemia, Lymphoma

clipboard icon

About Mercaptopurine

Mercaptopurine is a type of chemotherapy. It works by slowing or stopping the growth of cells. It is used in combination with other medicines.

Patients may differ in how slowly or quickly their body breaks down mercaptopurine due to the function of certain enzymes. A genetic test may be performed to see how well a patient’s enzymes function. Patients who break down mercaptopurine more slowly may receive a lower dose of the medicine. Read more: Thiopurine methyltransferase (TPMT) and medicines

Patients will have regular blood draws to check blood counts and monitor liver function. Blood levels of mercaptopurine may be monitored to see whether the dose should be changed.

liquid dropper icon

May be taken as a liquid by mouth

tablet and capsule icon

May be taken as a tablet by mouth

exclamation mark in a circle icon

Possible Side Effects

  • Low blood counts (may cause increased risk of infection, bleeding, anemia, and/or fatigue)
  • Liver problems
  • Nausea and vomiting (usually mild and occurs in the morning)
  • Hypoglycemia (low blood sugar)
  • Loss of appetite
  • Fatigue or weakness
  • Rash (may worsen when exposed to the sun)
  • Darkening of the skin
  • Increased sun sensitivity
  • Mouth sores
  • Diarrhea

Not all patients who take mercaptopurine will experience these side effects. Common side effects are in bold, but there may be others. Please report all suspected side effects to your doctor or pharmacist.

late effects icon

Possible Late Effects

Some patients may experience long-term or late effects of treatment that may continue or develop months or years after treatment ends. Possible late effects due to mercaptopurine include:

family icon

Tips for Families

Be sure to discuss these and other recommendations with your doctor or pharmacist.

  • A doctor may prescribe medicine to help with nausea and vomiting.
  • This medicine may make skin more sensitive to sunlight and increase risk for sunburn. Patients should take steps to protect skin from the sun. Wear sunscreen and protective clothing. Avoid sun exposure when possible.
  • Sexually active patients should take steps to prevent pregnancy during treatment and for 6 months after completion of therapy.
  • Patients should tell their doctor if they are pregnant or breastfeeding.
  • Caregivers should follow instructions for safe handling and disposal of chemotherapy and avoid contact with patient body fluids. Patient body fluids can contain the drug for 48 hours after it is given.

Mercaptopurine at home:

  • Take mercaptopurine at about the same time every day.
  • Store mercaptopurine at room temperature.
  • When giving liquid mercaptopurine, shake the bottle for at least 30 seconds before filling the oral syringe. Wash the syringe thoroughly after each use.
  • Give a missed dose as soon as possible. If it is near the time for the next dose (within 6 hours), skip the dose. Do not give 2 doses at the same time.
  • Do not use the medicine past the expiration date.
  • Follow instructions for safe handling and disposal.