Azathioprine is an immunosuppressive drug that is often prescribed after organ transplants, particularly kidney transplants. After a transplant, the body views the new organ as a foreign object and tries to eliminate it; this drug interferes with the immune system so that this doesn’t happen.
Any use of immunosuppressive drugs increases the risk of getting a serious infection or illness. Since the immune system doesn’t function normally, bacteria or viruses that normally would be eliminated can infect the body.
Azathioprine also increases the risk of certain cancers, especially lymphoma. Patients who suffer from inflammatory bowel syndrome are at particular risk of post-transplant lymphoma and hepatosplenic T-cell lymphoma after taking this medication. Both of these cancers are potentially fatal.