Methotrexate

Methotrexate is a drug. It is used to treat cancer and other autoimmune diseases. It can also be used to cause a medical abortion in the early stages of pregnancy.

Methotrexate Media

The coenzyme folic acid (top) and the anticancer drug methotrexate (bottom) are very similar in structure. As a result, methotrexate is a competitive inhibitor of many enzymes that use folates.
Methotrexate (green) complexed into the active site of DHFR (blue)
Image shows open bottle of methotrexate drug—one of the first chemotherapeutic drugs used in the early 1950s

This short article about medicine can be made longer. You can help Wikipedia by adding to it.