Mechanism of Action Methotrexate Tab, Methotrexate is a medication that works by inhibiting the activity of an enzyme called dihydrofolate reductase. This enzyme is essential for the synthesis of DNA, RNA, and proteins. By blocking it, methotrexate slows down the growth of rapidly dividing cells, such as cancer cells, and reduces inflammation in autoimmune diseases. Common Uses Methotrexate is c..