Fluorouracil (5-FU)

The chemotherapy drug fluorouracil is normally given together with other drugs to treat pancreatic cancer.

How is fluorouracil used?

The chemotherapy drug fluorouracil is normally given together with other drugs to treat pancreatic cancer.

  • It can be used with folinic acid (leucovorin), oxaliplatin and irinotecan in FOLFIRINOX.
  • It can be used with folinic acid and oxaliplatin in FOLFOX.

How is FOLFOX used?

FOLFOX may be used if you have locally advanced or advanced pancreatic cancer, and surgery to remove the cancer is not possible. It is used for people who have already had gemcitabine with capecitabine (GemCap) or gemcitabine with nab-paclitaxel.

Read more about FOLFIRINOX and how it is used.

How is fluorouracil given?

You will have your chemotherapy at the hospital as an outpatient. This means that you will go into the hospital for treatment, but won’t need to stay overnight.

Fluorouracil is given as an injection or an infusion into a vein. You may hear an infusion called a ‘drip’. You will have the infusion through a central line.

Fluorouracil is normally given together with other chemotherapy drugs as part of the chemotherapy treatments FOLFOX and FOLFIRINOX.

How is chemotherapy given?

What are the side effects of fluorouracil?

Fluorouracil can cause side effects, but these can affect everyone differently, and you may not get all of the side effects mentioned here. Your chemotherapy team should tell you about any possible side effects and how they are managed. Ask them any questions you have.

You can also speak to our specialist nurses on our free Support Line.


Fluorouracil is broken down in the body by an enzyme called dihydropyrimidine dehydrogenase (DPD). Some people have lower amounts of the DPD enzyme – which is known as DPD-deficiency.

People with DPD-deficiency can have side effects that are much worse than usual. These include infections, runny poo (diarrhoea) and feeling or being sick. It is important to speak to your chemotherapy team if you think you may have DPD deficiency, or would like to know more about it.

Your chemotherapy team should give you an emergency number to call if you are unwell, or if you need information about any side effects. Your nurse will explain when to use this number. If you haven’t been given a number, ask your nurse about this.

Common side effects


Fluorouracil can increase your risk of getting an infection. An infection is an emergency if you are having chemotherapy, and needs treating straight away. Read about the signs of an infection and how an infection is treated.

Anaemia (feeling tired or dizzy)

Fluorouracil can lower the number of red blood cells in your blood. This is called anaemia, and can make you feel tired, dizzy or short of breath.

Bruising and bleeding

Fluorouracil can lower the number of platelets in your blood – this is called thrombocytopenia. This can cause you to bruise more easily than normal, and you may be more likely to have nosebleeds or bleeding gums. Speak to your chemotherapy team straight away if you get any of these side effects.

Fatigue (extreme tiredness)

Fatigue is a common side effect of fluorouracil. It isn’t the same as feeling tired. Fatigue can make you feel weak and have problems concentrating. Some people find that the fatigue starts a few hours to a few days after having chemotherapy, and starts to get better after a few days. There are things that can help with fatigue.

Feeling or being sick (nausea or vomiting)

You will normally be given anti-sickness medicines before your chemotherapy starts. If these medicines don’t help, speak to your chemotherapy team about changing to a different medicine. We have tips on coping with feeling and being sick.

Runny poo (diarrhoea)

If you have diarrhoea, make sure you drink lots of water. If you have it more than four times a day, tell your chemotherapy team. They can give you medicines to control it. Read our tips on coping with diarrhoea.

Loss of appetite

During your treatment you may not feel like eating, and you may start to lose weight. Try to eat small meals often. If your appetite doesn’t get better after a few days, let your doctor or dietitian know. Read our tips on dealing with a loss of appetite.

Sore mouth or mouth ulcers

Fluorouracil can make your mouth sore, and cause mouth ulcers which can be uncomfortable. Tell your chemotherapy team about any problems you have with your mouth. They can make sure that you don’t have a mouth infection, and give you a mouthwash which should help.

Sore hands and feet

Fluorouracil can make the palms of your hands and the soles of your feet red and sore, and your skin may start to peel or blister. Your skin might also look shiny, feel tight and crack around the fingertips. Your doctor or nurse may give you a vitamin or creams to help with this. The soreness normally gets better when your chemotherapy finishes.

Hair loss

Fluorouracil may cause your hair to thin, or you may lose some hair – but it should grow back once your treatment stops.

Less common side effects

Heart problems

Fluorouracil can cause chest pain. It can also make you feel short of breath, dizzy, or cause an irregular heartbeat. It is important to call your chemotherapy team straight away if you have any of these symptoms, or go A&E and tell them that you are having chemotherapy.

Eye problems

Fluorouracil can cause sore, itchy or watery eyes. Tell your doctor or nurse if this happens, as they may need to give you some eye drops. Some people get blurred vision, but this is less common.

Skin changes

Fluorouracil can make your skin darken or become more sensitive to the sun. Use a high factor sun cream if you are going outside. These changes normally get better when your treatment finishes.


Fluorouracil can cause headaches. Tell your chemotherapy team if you have headaches, they can give you painkillers such as paracetamol or ibuprofen to help.

Risk of a blood clot in a vein

Fluorouracil can increase your risk of a blood clot in a vein, but this is not very common. If you have any pain or swelling in one of your arms or legs, or you feel very short of breath, call your chemotherapy team straight away. Or phone an ambulance. A blood clot is serious if it isn’t treated.

Questions about side effects?

Speak to your doctor or nurse about side effects, or if you would like more information.

You can also speak to our specialist nurses on our Support Line.

Speak to our nurses
Specialist nurse Nicci

Read about Fluorouracil (5-FU) in our fact sheet

You can download our fact sheet, Fluorouracil for pancreatic cancer.

Download our fact sheet

Updated August 2019

Review date August 2021