Azathioprine (AZA), sold under the brand name Imuran among others, is an immunosuppressive medication. It is used in rheumatoid arthritis, granulomatosis with polyangiitis, Crohn's disease, ulcerative colitis, systemic lupus erythematosus, and in kidney transplants to prevent rejection. It is taken by mouth or injected into a vein. Azathioprine (AZA), sold under the brand name Imuran among others, is an immunosuppressive medication. It is used in rheumatoid arthritis, granulomatosis with polyangiitis, Crohn's disease, ulcerative colitis, systemic lupus erythematosus, and in kidney transplants to prevent rejection. It is taken by mouth or injected into a vein. Common side effects include bone marrow suppression and vomiting. Bone marrow suppression is especially common in people with a genetic deficiency of the enzyme thiopurine S-methyltransferase. Other serious risk factors include an increased risk of lymphoma. Use during pregnancy may result in harm to the baby. Azathioprine is in the purine analogue and antimetabolite family of medication. It works via 6-thioguanine to disrupt the making of RNA and DNA by cells. Azathioprine was first made in 1957. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. The wholesale cost in the developing world is about US$7.63–17.19 a month. The wholesale cost in the United States is about US$35.34 per month. In 2016 it was the 219th most prescribed medication in the United States with more than 2 million prescriptions. Azathioprine is used alone or in combination with other immunosuppressive therapy to prevent rejection following organ transplantation, and to treat an array of autoimmune diseases, including rheumatoid arthritis, pemphigus, systemic lupus erythematosus, Behçet's disease, and other forms of vasculitis, autoimmune hepatitis, atopic dermatitis, myasthenia gravis, neuromyelitis optica (Devic's disease), restrictive lung disease, and others. It is also an important therapy and steroid-sparing agent for inflammatory bowel disease (such as Crohn's disease and ulcerative colitis) and for multiple sclerosis. In the United States, it is currently approved by the Food and Drug Administration (FDA) for use in kidney transplantation from human donors, and for rheumatoid arthritis. Azathioprine is used to prevent rejections of kidney or liver allografts, usually in conjunction with other therapies including corticosteroids, other immunosuppressants, and local radiation therapy. The administration protocol starts either at the time of transplantation or within the following two days. Being a disease-modifying antirheumatic drug (DMARD), azathioprine has been used for the management of the signs and symptoms of adult rheumatoid arthritis. Nonsteroidal anti-inflammatory drugs (NSAIDs) and corticosteroids may be combined or continued (if they were already in use) with azathioprine, but the combination with other DMARDs is not recommended. Azathioprine has been used in the management of moderate to severe chronically active Crohn's disease, to maintain clinical remission (absence of disease activity) in corticosteroid-dependent patients, and to provide benefit in people with fistulizing Crohn's disease. The onset of action is slow and it may require several months to achieve clinical response. Azathioprine treatment is associated with an increased risk of lymphoma, but it is unclear if this is due to the drug or a predisposition related to Crohn's disease. Lower doses of azathioprine are used as a therapy in children with refractory or corticosteroid-dependent Crohn's disease, without causing many side effects.