Side Effects of Imuran (Azathioprine)

Certain side effects should be reported to your physician right away.

Imuran (azathioprine) is an immunosuppressive antimetabolite drug that may be prescribed to treat conditions such as inflammatory bowel disease (IBD) or rheumatoid arthritis. Imuran might also be used in patients who have had an organ transplant in order to prevent the body from rejecting the organ. This drug suppresses the immune system. In most cases, Imuran is used to treat IBD after other drugs have not worked. It might also be used at the same time as steroids.

Medications that affect the immune system might increase the risk of developing an infection, and precautions might need to be taken to protect against infections. People taking Imuran should not receive any live vaccines. It might also be necessary to avoid people who are sick. Any sign of infection should be discussed with a doctor right away.

Imuran pills
Samir / CC by 3.0

Black Box Warning

Imuran tablets contain a black box warning related to the possibility of developing a specific kind of cancer. This is related in particular to people who take the drug and also have IBD. The risk of developing cancer should be weighed against the risk of not treating the IBD with this drug.

Cancer risks in people with IBD are still an ongoing topic for debate and study, so it is important to take a common sense approach when considering the risks. Some studies have shown a risk, but others have not. Be sure to discuss this potential adverse effect with your physicians so that you can understand your individual risk.

"Chronic immunosuppression with Imuran, a purine antimetabolite increases risk of malignancy in humans. Reports of malignancy include post-transplant lymphoma and hepatosplenic T-cell lymphoma (HSTCL) in patients with inflammatory bowel disease. Physicians using this drug should be very familiar with this risk as well as with the mutagenic potential to both men and women and with possible hematologic toxicities. Physicians should inform patients of the risk of malignancy with Imuran."

Side Effects

The following include the most common side effects of using Imuran. Check with your doctor if any of the listed side effects continue or are bothersome:

  • Loss of appetite
  • Nausea or vomiting

Less commonly, skin rash may occur.

Severe Side Effects

Notify your physician if you develop any of the following symptoms while taking Imuran.

  • Cough, hoarseness
  • Fever or chills
  • Lower back or side pain
  • Painful or difficult urination
  • Unusual tiredness, weakness
  • Black, tarry stools
  • Blood in urine or stools
  • Pinpoint red spots on the skin
  • Unusual bleeding or bruising

Rarely, the following severe side effects may occur:

  • Fast heartbeat
  • Fever (sudden)
  • Muscle or joint pain
  • Nausea, vomiting, and diarrhea (severe)
  • Redness or blisters on the skin
  • Shortness of breath
  • Sores in the mouth, on lips
  • Stomach pain
  • Swelling of feet or lower legs
  • A feeling of discomfort or illness (sudden)


Your doctor will watch for any liver problems this medicine may cause.

Because of the way this medicine acts on the body, there is a chance that it might cause other unwanted effects that may not occur until months or years after the medicine is used. According to a study published in 2010, taking azathioprine was associated with a greater risk of lymphomas but not other types of cancers.

After you stop this medicine, there may still be some side effects. During this time notify your doctor as soon as possible if you notice any of the following:

  • Black, tarry stools
  • Blood in urine
  • Cough or hoarseness
  • Fever or chills
  • Lower back or side pain
  • Painful or difficult urination
  • Pinpoint red spots on the skin
  • Unusual bleeding or bruising

A Word From Verywell

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor. This information is meant only as a guideline—always consult a physician or pharmacist for complete information about prescription medications.

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  1. U.S. Food and Drug Administration. IMURAN (azathioprine). Updated May 2011.

  2. Armstrong RG, West J, Card TR. Risk of cancer in inflammatory bowel disease treated with azathioprine: a UK population-based case-control study. Am J Gastroenterol. 2010;105(7):1604-9. doi:10.1038/ajg.2009.745