Ulcerative colitis is an autoimmune disease, which means it causes your immune system to attack parts of your body. With it, your immune system causes inflammation and ulcers in the lining of your colon. Ulcerative colitis can be more active at times and less active at others. When it’s more active, you have more symptoms. These times are called flare-ups.

To help prevent flare-ups, you can try to decrease the amount of fiber in your diet or avoid certain foods that are too spicy, but most people with ulcerative colitis also need the help of drugs. Imuran is a medication that can help manage your symptoms of ulcerative colitis, including stomach cramps and pain, diarrhea, and bloody stool.

Doctors usually prescribe Imuran for people who have tried other drugs that didn’t help relieve their symptoms, such as aminosalicylates and corticosteroids. Imuran is a brand-name oral tablet of the generic drug azathioprine. It belongs to a class of drugs called immunosuppressants, so it works by decreasing your immune system response. This effect reduces inflammation, keeps your symptoms in check, and lowers the chance of flare-ups. It’s used for long-term management of symptoms of mild to moderate ulcerative colitis. However, this is an off-label use of Imuran.

It may take up to six months for Imuran to begin to relieve your symptoms. Imuran can reduce the damage from inflammation that can lead to hospital visits and the need for surgery. It’s also been shown to reduce the need for corticosteroids that are often used to treat ulcerative colitis. This can be beneficial: corticosteroids can cause more side effects when used for long periods.

Imuran can also cause potentially serious side effects, though. While taking it, it’s a good idea to see your doctor as often as they suggest. That way, they can watch you closely for side effects. The milder side effects of Imuran can include nausea and vomiting. The more severe side effects of this drug are below.

Increased risk of certain types of cancer

Using Imuran for a long time may increase your risk of skin cancer and lymphoma. Lymphoma is a cancer that affects your immune cells.

More infections

Imuran lowers the activity of your immune system. This means your immune system may not work as well to fight off infections. As a result, infections are a fairly common side effect. Even though they’re common, infections can still be serious.

Allergic reaction

Symptoms of an allergic reaction usually happen within the first few weeks of treatment. They include:

  • nausea
  • vomiting
  • diarrhea
  • rash
  • fever
  • tiredness
  • muscle aches
  • dizziness

If you have these symptoms, contact your doctor right away.


Inflammation of the pancreas is a rare side effect from Imuran. If you have symptoms such as severe stomach pain, vomiting, or oily stools, call your doctor right away.

Your doctor may suggest Imuran if drugs like aminosalicylates and corticosteroids haven’t worked to control your symptoms from ulcerative colitis. It may help reduce flare-ups and keep your symptoms under control. Imuran comes with the risk of serious side effects, including an increased risk of cancer and infections. Only you and your doctor can decide if this drug is a good choice for you.