Folinic acid, also known as leucovorin, is a form of vitamin B9 that helps the body produce and maintain new cells. It is often used to reduce the side effects of certain cancer treatments, particularly those involving methotrexate, a chemotherapy drug. Folinic acid can enhance the effectiveness of some medications and is important for DNA synthesis and repair. In addition to its use in cancer therapy, folinic acid is also utilized in treating megaloblastic anemia, a condition caused by a deficiency of folate. It can be administered orally or through injection, depending on the patient's needs and the specific medical situation.