Methotrexate (MTX), formerly known as amethopterin, is a chemotherapy agent and immune-system suppressant. It is used to treat cancer, autoimmune diseases, ectopic pregnancy, and for medical abortions. Types of cancers it is used for include breast cancer, leukemia, lung cancer, lymphoma, gestational trophoblastic disease, and osteosarcoma. Types of autoimmune diseases it is used for include psoriasis, rheumatoid arthritis, and Crohn's disease. It can be given by mouth or by injection.Common side effects include nausea, feeling tired, fever, increased risk of infection, low white blood cell counts, and breakdown of the skin inside the mouth. Other side effects may include liver disease, lung disease, lymphoma, and severe skin rashes. People on long-term treatment should be regularly checked for side effects. It is not safe during breastfeeding. In those with kidney problems, lower doses may be needed. It acts by blocking the body's use of folic acid.Methotrexate was first made in 1947, and initially was used to treat cancer, as it was less toxic than the then-current treatments. In 1956 it provided the first cures of a metastatic cancer. It is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system. Methotrexate is available as a generic medication. In 2017, it was the 117th most commonly prescribed medication in the United States, with more than six million prescriptions.