A drug used to treat many types of cancer. It is also used to treat rheumatoid arthritis and severe psoriasis (a type of skin condition). Methotrexate stops cells from using folic acid to make DNA and may kill cancer cells. It may also lower the body’s immune response. Methotrexate is a type of antimetabolite and a type of antifolate. Also called amethopterin, MTX, Rheumatrex, and Trexall.