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Brand names:


Other names:

6-Thioguanine, 6-TG, TG, Tioguanine, 2-Amino-6-Mercaptopurine

Often used for:


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What is Thioguanine?

Thioguanine is a type of chemotherapy. It works by slowing or stopping the growth of cells.

Patients may differ in how slowly or quickly their body breaks down thioguanine 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 thioguanine more slowly may receive a lower dose of the medicine. Read more about thiopurine methyltransferase (TPMT) and medicines.

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May be taken as a tablet by mouth

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May be taken as a liquid by mouth

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Possible Side Effects

  • Nausea and vomiting
  • Low blood counts (may cause increased risk of infection, bleeding, anemia, and/or fatigue)
  • Liver problems
  • Loss of appetite
  • Mouth sores
  • Tumor lysis syndrome
  • Mild swelling of the legs, hands, feet, or feeling more “bloated” (increase in water weight)

Not all patients who take thioguanine 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.

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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 thioguanine include:

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Tips for Families

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

  • 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 a period of time 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.

Thioguanine at home:

  • Take thioguanine at about the same time every day.
  • Give a missed dose as soon as possible. If it is within 12 hours of the time for the next dose, skip the dose. Do not give 2 doses at the same time.
  • Store thioguanine at room temperature.
  • When giving liquid thioguanine, shake bottle well before use.
  • Syringes for liquid medicine should be thrown away after each use. Do not reuse.
  • Do not use the medicine past the expiration date.
  • Follow instructions for safe handling and disposal.