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Although the exact cause of the disease is unclear, its origins appear to have something to do with the body’s immune system. Either the immune system reacts too aggressively to an infection, or mistakes the intestinal contents (both food products and naturally-occurring intestinal bacteria) as a threat. The immune system floods the area with white blood cells, resulting in painful inflammation.

Certain drugs suppress the immune system, which in turn reduces inflammation and provides pain relief. While low doses of immune system suppressants are often administered for Crohn’s disease, some risks are involved. Because the immune system is suppressed, the chances of serious infection are higher than normal. This, and other possible side effects, must be balanced against the pain relief they provide.

What are Immune System Suppressants?

An immune suppressant controls inflammation by blocking the body’s immune system. An immune system suppressant can provide much-needed pain relief, but raises the risk of infections from other sources.

Consult your doctor immediately if the following side effects occur:

  • blood in your urine
  • black “tar-like” stools
  • rapid heartbeat
  • vision problems
  • yellowing of your skin
  • shortness of breath.

Azathioprine and 6MP

Azathioprine and 6MP are two closely related medications. Azathioprine actually breaks down into 6MP in the intestinal tract. Both are immune system suppressants and provide pain relief. Seventy percent of patients with moderate to severe Crohn’s symptoms respond to these medications, although it may take up to three months of treatment before symptoms improve.

While they have fewer side effects than corticosteroids, these medications can also have serious side effects. Those taking 6MP may have an increased risk of cancer, and both medications can cause low white blood cell counts. (Some reduction of white blood cells is necessary for the medication to work, and is to be expected.) Taking either azathioprine or 6MP with bone marrow medications or ACE inhibitors used to control high blood pressure can contribute to low white blood cell counts. Inflammation of the liver and the pancreas may also occur.

Both azathioprine and 6MP can produce irregular menstrual cycles and lowered sperm counts. Neither medication should be taken while pregnant or breastfeeding. While taking either medication, regular blood tests will be taken to monitor both white blood cell counts and liver function.

Some of the common side effects of azathioprine and 6MP are nausea, vomiting and loss of appetite.


An alternative to azathioprine and 6MP, methotrexate is both an immune system suppressant and an anti-inflammatory. It also produces faster results than older immune suppressants. Methotrexate can be taken in tablet form or through weekly injections. Like azathioprine and 6MP, it can cause low white blood cell counts. Years of use can result in cirrhosis of the liver, lung inflammation, bone marrow damage and an increased risk of cancer. The side effects of methotrexate are, in general, similar to those of 6MP and azathioprine: nausea, vomiting and loss of appetite.


Centocor, Inc. (nd). Treatment for Crohn’s disease.

National Digestive Diseases Information Clearinghouse. (2003, January). Crohn’s disease [NIH Publication No. 03-3410].

 Posted on : May 17, 2014