Thioguanine is used to treat acute myeloid leukemia (AML; a type of cancer that begins in the white blood cells). Thioguanine is in a class of medications known as purine analogs. It works by slowing or stopping the growth of cancer cells in your body.

Side Effects Of Thioguanine

Thioguanine may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

Some side effects can be serious. If you experience any of these symptoms, call your doctor immediately:

  • unusual tiredness or weakness
  • unusual bleeding or bruising
  • yellowing of the skin or eyes
  • flu-like symptoms
  • swelling of the stomach area
  • stomach pain, particularly in the right part of the stomach
  • swelling of the face, arms, hands, feet, ankles, or lower legs
  • bloody vomit
  • black, tarry, or bloody stools
  • fever, sore throat, ongoing cough, and congestion, or other signs of infection
  • shortness of breath
  • lightheadedness

Thioguanine may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.

Warnings & Precautions

Before taking thioguanine:

  • tell your doctor and pharmacist if you are allergic to thioguanine, any other medications, or any of the ingredients in thioguanine tablets. Ask your pharmacist for a list of the ingredients.
  • tell your doctor if you have already taken thioguanine or mercaptopurine to treat your cancer. Your doctor may tell you not to take thioguanine if either of these medications did not work well against your cancer in the past.
  • tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: aminosalicylates such as mesalamine (Apriso, Asacol, Pentasa, others), olsalazine (Dipentum), and sulfasalazine (Azulfidine). Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Also, tell your doctor and pharmacist about all the medications you are taking so they can check whether any of your medications may increase the risk that you will develop liver damage during your treatment with thioguanine.
  • tell your doctor if you have or have ever had liver disease.
  • tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. You should not become pregnant or breast-feed while you are receiving thioguanine. If you become pregnant while receiving thioguanine, call your doctor. Thioguanine may harm the fetus.
  • do not have any vaccinations without talking to your doctor.
  • you should know that the risk that you will develop serious side effects of thioguanine may be higher if you have a genetic (inherited) risk factor. Your doctor may order tests before or during your treatment to see if you have this risk factor.

Thioguanine Dosage

Thioguanine comes as a tablet to take by mouth usually once a day. The length of treatment depends on the types of drugs you are taking, how well your body responds to them, and the type of cancer you have. Take thioguanine at around the same time every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take thioguanine exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Your doctor may increase or decrease your dose of thioguanine during your treatment. This depends on how well the medication works for you and on the side effects that you experience. Talk to your doctor about how you are feeling during your treatment. Continue to take thioguanine even if you feel well. Do not stop taking thioguanine without talking to your doctor

Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient.


Keep all appointments with your doctor and the laboratory. Your doctor may order certain lab tests to check your body’s response to thioguanine.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.


All information has been provided courtesy of MedLinePlus from the National Library of Medicine and from the FDA.