Leucovorin calcium is a folic acid analog used primarily to prevent or reduce the harmful effects of methotrexate, a chemotherapy medication. It works by supplying a form of folate that bypasses the inhibition caused by methotrexate, protecting healthy cells and reducing toxicity. Leucovorin is also used to treat certain types of anemia related to folic acid deficiency and as an adjunct in colorectal cancer treatment to enhance the efficacy of drugs like fluorouracil. It is available in oral and injectable forms and is sometimes given following high-dose methotrexate therapy or overdoses to counteract adverse effects.