5-fluorouracil (5-FU) is a chemotherapy medication primarily used to treat various types of cancer, including breast cancer, colon cancer, and stomach cancer. It works by interfering with the growth of cancer cells, preventing them from multiplying and spreading in the body. 5-FU is often administered intravenously or as a topical cream for certain skin cancers. Common side effects include nausea, vomiting, and a decrease in blood cell counts, which can increase the risk of infections. Regular monitoring by healthcare professionals is essential during treatment to manage these side effects effectively.