Leucovorin Calcium Injection is a medication used to treat folate deficiency and certain types of cancer, such as colorectal cancer and metastatic breast cancer. It works by restoring folate levels in the body, which helps to reduce the side effects of chemotherapy and radiation therapy. It is usually given as an IV injection or an oral tablet. The most common side effects of Leucovorin Calcium Injection include nausea, constipation, vomiting, and diarrhea.