Antimetabolites (folic acid antagonists)
Antimetabolites interfere with the building blocks cells need to make DNA, which slows rapidly dividing cells such as cancer cells and overactive immune cells. Methotrexate treats certain cancers and, at much lower once-weekly doses, rheumatoid arthritis, juvenile arthritis, and severe psoriasis. Mouth sores, nausea, tiredness, and abnormal liver tests are common. It can seriously harm the bone marrow, liver, lungs, and kidneys and cause birth defects, and taking a once-weekly dose every day by mistake has caused deaths.