What is the mechanism of action of methotrexate?

Methotrexate works by inhibiting an enzyme known as dihydrofolic acid reductase (also known as dihydrofolate reductase). This enzyme is important for transforming an inactive form of folic acid into the active form, which is necessary to make some of the building blocks needed for DNA production. By inhibiting this enzyme, methotrexate interferes with a cell's ability to repair and replicate (copy) itself.

Although this drug can damage healthy cells as well as unhealthy cells, it tends to target rapidly replicating cells, such as cancer cells and bone marrow cells.

It is not entirely clear how methotrexate works to treat rheumatoid arthritis, although it is thought to work by affecting the immune system.

However, please for more info do talk to a doc/pharmacist, take care.

Best wishes!