Used as an antidote to prevent or reduce toxicity caused by high-dose methotrexate therapy, particularly in cancer treatment. Enhances the recovery of healthy cells by providing a source of reduced folate, which supports DNA synthesis and cell division. Commonly administered in oncology settings during high-dose methotrexate regimens for cancers such as osteosarcoma or lymphoma. Also used to treat accidental overdoses of folic acid antagonists. Helps protect bone marrow and gastrointestinal tissues from damage while allowing methotrexate to maintain its therapeutic effect on tumor cells.