Azathioprine Tablet belongs to a group of medicines called immunosuppressants. It is used with other medicines to prevent your body rejecting an organ (such as a kidney, heart or liver) after a transplant. It is also used in the treatment of rheumatoid arthritis.It has many potential side effects. The most common are loss of appetite, nausea, and increased risk of bleeding. Because it suppresses your immune system, you may catch more infections than usual. There’s also an increased risk of developing some cancers for this reason.