5-Fluorouracil is a chemotherapy medication commonly used in colorectal, breast, stomach, and pancreatic cancers. It is often administered as part of combination treatment strategies.

It is an antimetabolite drug that mimics naturally occurring substances within the cell.

5-FU works by interfering with thymidylate synthase, an enzyme required for DNA synthesis. By disrupting this pathway, it may prevent cancer cells from replicating their DNA and dividing effectively.

Because it also affects normal rapidly dividing cells, particularly in the gastrointestinal tract and bone marrow, side effects such as diarrhea, mouth sores, or low blood counts may occur.