Azathioprine is a medication used to manage autoimmune conditions like rheumatoid arthritis and inflammatory bowel disease, also atopic dermatitis, as well as to prevent organ rejection after transplants. It works by reducing the activity of the immune system to help control inflammation and prevent the body from attacking its own tissues. Typically taken as a pill, it's monitored by healthcare providers to ensure safe, long-term use and to maintain the balance between effectiveness and minimal side effects.