Fluorouracil (also called 5-FU) is a chemotherapy medicine. You receive it by IV, often alone or with other drugs. It helps treat several types of cancer by slowing or stopping cancer cell growth.
Brand Name(s)
- Generic: fluorouracil (5-FU)
- Injection (for cancer): Adrucil (U.S.) and generics
- Topical creams (for skin conditions, not cancer treatment): Efudex, Carac, Fluoroplex
Warning(s)
Read these safety points before and during treatment. This list is not complete.
- Allergies: Do not use if you are allergic to fluorouracil or any ingredient in it. Tell your care team about all drug and food allergies you have had.
- DPD deficiency: Some people lack an enzyme called dihydropyrimidine dehydrogenase (DPD). This greatly raises the risk of severe side effects (mouth sores, diarrhea, low white blood cells, nerve problems). Your team may check for this.
- Low blood counts: This drug can lower white cells, red cells, and platelets. That can lead to infections, anemia, or bleeding. You will need regular blood tests.
- Infection and bleeding risk: Wash your hands often. Stay away from people who are sick. Use a soft toothbrush and an electric razor to reduce bleeding.
- Severe stomach and gut effects: Diarrhea, vomiting, and poor appetite can occur and may cause dehydration or electrolyte problems. Report worsening symptoms promptly.
- Heart effects: Chest pain, heart attack, heart failure, or abnormal heartbeat can happen, especially if you have heart disease. Get urgent care for chest pain, shortness of breath, or a racing/irregular heartbeat.
- Nervous system effects: Confusion, severe sleepiness, balance changes, headache, or vision changes can occur. Rarely, eye movement problems or stiff neck happen.
- Sun sensitivity: Your skin may burn more easily. Use sunscreen, protective clothing, and limit sun exposure.
- Vaccines: Some vaccines may not work as well or may raise infection risk while you are on chemotherapy. Ask your care team before any vaccines.
- Pregnancy and breastfeeding: This drug can harm an unborn baby. Use effective birth control during treatment and for a period after your last dose. Do not breastfeed while taking this drug (and for some time after). Ask how long you need to use birth control and avoid breastfeeding.
- Fertility: This drug may affect the ability to get pregnant or father a child. If future fertility is important to you, discuss options before treatment.
- IV site problems: The drug can irritate the vein, and if it leaks under the skin, it can cause tissue damage. Tell your nurse right away if you feel burning, pain, swelling, or see redness where the IV goes in.
- Other conditions and medicines: Tell your care team about infections, poor nutrition, or any bone marrow problems. Share a full list of all medicines, vitamins, and herbal products you take to check for interactions.
- Care coordination: Tell all your healthcare providers, including your dentist, that you receive fluorouracil.
Kind of Cancers It Is Used For (not a complete list)
- Colorectal cancer (colon and rectal)
- Stomach (gastric) and esophageal cancers
- Pancreatic cancer (often part of combination regimens)
- Breast cancer
- Head and neck cancers
- Anal cancer (often with radiation)
- Some biliary tract cancers
Your care team may use fluorouracil with other drugs (for example, leucovorin) or with radiation in certain cancers.
Mechanism of Action
- Fluorouracil is an antimetabolite (a pyrimidine analog). It looks like a normal building block of DNA and RNA.
- Inside cells, it is changed into active forms that block thymidylate synthase, an enzyme cancer cells need to make DNA. This stops cells from dividing.
- It can also be built into RNA and DNA, disrupting how cells function and survive.
- It mainly targets fast-growing cells, like many cancer cells. Leucovorin is sometimes given with 5-FU to boost its effect.
Common Side Effects
- Tiredness or weakness
- Low blood counts (may lead to infections, anemia, easy bruising or bleeding)
- Diarrhea, nausea, vomiting, decreased appetite
- Mouth irritation or mouth sores
- Hand-foot syndrome (redness, swelling, tenderness, or peeling of palms and soles)
- Dry or itchy skin; nail changes; skin darkening; increased sun sensitivity
- Hair thinning or hair loss
- Watery or irritated eyes; tearing; changes in taste
- Injection site pain, redness, or swelling
Not everyone has all these effects. Tell your care team if side effects are severe, do not improve, or feel concerning.
Fluorouracil (5-FU) MedlinePlus
Last reviewed: 2025-11-28
