Fluorouracil is a chemotherapy drug that is used to treat a variety of cancers, mainly breast, skin and gastrointestinal cancers. Chemically, it is classified as an antimetabolite and it interferes with cell growth (it is classed as both an antineoplastic and an antimetabolite). Its trade names include Fluorouracik and Adrucil.

It is given intravenously (as a clear fluid), orally (as blue/orange capsules of 250mg and 500mg), and as a topical cream. The drug may cause mouth sores, gastrointestinal upsets like nausea and diarrhea, skin changes, bone marrow suppression, and it may also harm developing fetuses.