While cytotoxic drugs are usually used to treat people who have cancer or have received organ transplants, they are also used for some individuals who have severe arthritis.

These drugs work by suppressing the immune system and thereby block the actions of cells that create the abnormal antibodies in autoimmune diseases and of those that are involved in inflammation. However, because cytotoxic drugs are very potent and have serious side effects, physicians use them only in cases where other drugs have not been effective. The most frequently used cytotoxic drugs are cyclophosphamide and azathioprine (generic names).

Methotrexate, a drug used to treat cancer, is also becoming more widely used to treat rheumatoid arthritis, psoriatic arthritis, and in certain situations, in connective tissue diseases.