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What is thioguanine?

Thioguanine (also called 6-TG or 6-thioguanine) is an anticancer medicine. Thioguanine is available as a beige 40-mg tablet and as an oral liquid taken by mouth.

Laboratory testing of thioguanine

Two enzymes in the body called thiopurine methyltransferase (TPMT) and nudix type motif 15 (NUDT15) have the ability to break down certain medicines, including thioguanine. A genetic test can be done to determine how well your TPMT and NUDT15 enzymes break down medicines. If your body breaks down the medicine slower than most people, you should receive lower doses of thioguanine.  For information about both TPMT and NUDT15 and their effect on thioguanine, talk with your doctor or pharmacist, and see “Do You Know… Thiopurine methyltransferase (TPMT) and medicines.” For more details, go to

Possible side effects of thioguanine


  • Mild nausea
  • Mild vomiting
  • Decreased appetite
  • Rash

Later (more than a day after treatment starts)

  • Low blood counts
  • Mouth sores
  • Decreased liver function

These are the most common side effects, but there may be others. Please report all side effects to the doctor or nurse. In case of a severe side effect or reaction, call the doctor, nurse, or pharmacist at 901-595-3300. If you are outside the Memphis area, dial toll-free 1-866-2STJUDE (1-866-278-5833), and press 0 once the call is connected.

Pregnancy risk and thioguanine

This medicine may be harmful to the unborn child. Avoid becoming pregnant during treatment. Contact one of your caregivers at St. Jude if you are sexually active or think you may be pregnant.

Special instructions for thioguanine

  • Thioguanine should be taken every day. It is very important that you take your medicine as your doctor tells you. If you do not take your medicine regularly, your disease if more likely to come back.
  • If you miss a dose, take the dose as soon as you remember, as long as it is at least 6 hours before the next scheduled dose.
  • If you have nausea or vomiting, tell your doctor. The doctor can prescribe medicine to keep you from feeling sick and throwing up while you are taking thioguanine.
  • Store thioguanine tablets and liquid at room temperature in a dry place. Do not use the liquid medicine after the expiration date printed on the label.
  • The staff will take blood samples regularly to check for changes in liver function and to check blood counts.

Safe handling of thioguanine

All chemotherapy drugs taken by mouth can pose a health hazard to caregivers and patients. You should be careful when handling this medicine and try to keep the drug from touching skin. Taking precautions will ensure that both the patient and caregiver are protected as well as possible.

  • Prepare a clean area where the drug can be handled safely (away from areas where food is prepared, out of the reach of children, and out from under any air vents or fans).
  • We suggest you or the caregiver wear gloves while handling this medicine. Wash your hands right away if your skin comes in contact with the medicine.
  • Carefully wash tablet cutters with warm soapy water after each use and allow to dry. Completely clean up any spills in the area where the medicine is prepared.
  • For the liquid, St. Jude will provide enough oral syringes for each dose. Use each oral syringe only one (1) time and then discard it in the trash. Do not try to wash and reuse the syringes.


This document is not intended to take the place of the care and attention of your personal physician or other professional medical services. Our aim is to promote active participation in your care and treatment by providing information and education. Questions about individual health concerns or specific treatment options should be discussed with your physician.

St. Jude complies with health care-related federal civil rights laws and does not discriminate on the basis of race, color, national origin, age, disability, or sex.

ATTENTION: If you speak another language, assistance services, free of charge, are available to you. Call 1-866-278-5833 (TTY: 1-901-595-1040).

ATENCIÓN: si habla español, tiene a su disposición servicios gratuitos de asistencia lingüística. Llame al 1-866-278-5833 (TTY: 1-901-595-1040).

تنبيه: إذا كنت تتحدث باللغة العربية فيمكنك الاستعانة بخدمات المساعدة اللغوية المتوفرة لك مجانا. .يرجى الاتصال بالرقم. 5833-278-866-1  (الهاتف النصي: 1040-595-901-1).