Methotrexate is used in the treatment of leukemia, lymphoma, breast cancer, and osteosarcoma, and it is also used in lower doses for certain autoimmune diseases.

It belongs to a class of drugs known as antimetabolites, which interfere with the metabolic processes required for cell growth.

Methotrexate works by inhibiting the enzyme dihydrofolate reductase (DHFR), which is essential for the production of DNA and RNA building blocks. By limiting these components, methotrexate may slow or stop the proliferation of cancer cells.

Because normal cells also rely on these processes, especially those that divide rapidly, methotrexate may affect healthy tissues, leading to side effects such as mouth sores, fatigue, or bone marrow suppression.