Cancer drugs A to Z list
Fluorouracil is a type of chemotherapy. It is also known as 5FU. You pronounce fluorouracil as floor-oh-yoor-uh-sil.
It is a treatment for a number of different cancer types. You usually have it in combination with other cancer drugs. You might also have it alongside .
Find out about treatment for your cancer type
Fluorouracil is part of a group of chemotherapy drugs known as . Anti-metabolites are similar to normal body molecules but they have a slightly different structure.
These differences mean that anti-metabolites stop cancer cells working properly. They stop the cells making and repairing . Cancer cells need to make and repair DNA so that they can grow and multiply.
You have fluorouracil as a drip into your bloodstream (intravenously).
You might have treatment through a long plastic tube that goes into a large vein in your chest. The tube stays in place throughout the course of treatment. This can be a:
central line
PICC line
portacath
You might have treatment through a thin short tube (a cannula) that goes into a vein in your arm. You have a new cannula each time you have treatment.
You may have fluorouracil via a pump that you carry around for several days.
Fluorouracil is available as a cream for skin cancer. The cream doesn’t usually cause many side effects, but it can cause temporary irritation and inflammation in the treated areas of skin.
You usually have fluorouracil as a course of several cycles of treatment. This means that you have the drug and then a rest to allow your body to recover.
How often you have fluorouracil can vary depending on your cancer type. Your doctor or nurse will explain your treatment to you.
You might have continuous treatment through a portable pump. The nurse attaches it to your central line. This means you can go home with it. A nurse disconnects your pump before your next cycle of treatment. This may happen in the hospital or at home.
You have blood tests before and during your treatment. They check your levels of and other substances in the blood. They also check how well your liver and kidneys are working.
Before treatment starts you may have a blood test to check for viruses such as hepatitis B, hepatitis C, and HIV. This is called a viral screen.
It’s important for your doctor to know if you have had any of these viruses. This is because this treatment can weaken your and can cause the virus to become active again (reactivation).
Before starting treatment with 5FU you have a blood test to check levels of an enzyme called dihydropyrimidine dehydrogenase (DPD). A low DPD level means you are more likely to have severe side effects from this chemotherapy, so you may start treatment with a lower amount (dose) of the drug or have a different treatment. Your doctor, nurse or pharmacist will talk to you about this.
Side effects can vary from person to person. They also depend on what other treatment you are having.
Your doctor, pharmacist or nurse will go through the possible side effects. They will monitor you closely during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:
you have severe side effects
your side effects aren’t getting any better
your side effects are getting worse
the side effects are affecting your daily life
Early treatment can help manage side effects better.
We haven't listed all the side effects here. Talk to your healthcare team if you have any new symptoms that you think might be a side effect of your treatment.
Remember it is very unlikely that you will have all of these side effects, but you might have some of them at the same time.
These side effects happen in more than 10 in 100 people (more than 10%). You might have one or more of them. They include:
Increased risk of getting an infection is due to a drop in . Symptoms include a change in temperature, aching muscles, cough, headaches, feeling cold and shivery, pain or a burning feeling when peeing or generally feeling unwell. You might have other symptoms depending on where the infection is.
Infections can sometimes be life threatening. You should contact your advice line urgently if you think you have an infection.
You might be breathless and look pale due to a drop in . This is called anaemia.
This is due to a drop in the number of platelets in your blood. These blood cells help the blood to clot when we cut ourselves. You may have nosebleeds or bleeding gums after brushing your teeth. Or you may have lots of tiny red spots or bruises on your arms or legs. This is known as petechiae.
Contact your advice line if you have diarrhoea. For example, in one day you have 2 or more loose bowel movements than usual. If you have a , you might have more output than normal. Your doctor may give you anti diarrhoea medicine to take home with you after treatment.
Try to eat small meals and snacks regularly. It’s best to try to have a healthy balanced diet if you can. You don’t necessarily need to stop eating foods that contain . But if your diet is normally very high in fibre, it might help to cut back on high fibre foods such as beans, nuts, seeds, dried fruit, bran and raw vegetables.
Drink plenty to try and replace the fluid lost. Aim for 8 to 10 glasses per day.
Feeling or being sick is usually well controlled with anti sickness medicines. It might help to avoid fatty or fried foods, eat small meals and snacks and take regular sips of water. Relaxation techniques might also help.
It is important to take anti sickness medicines as prescribed even if you don’t feel sick. It is easier to prevent sickness rather than treat it once it has started.
You might have a sudden feeling of tightness in your chest, difficulty catching your breath, wheezing and a cough. This is caused by spasms and tightening of the muscles of your airways. Contact your healthcare advice line or tell your doctor.
You may get changes to your heart rhythm picked up on a . Less commonly you might get chest pains.
Rarely you might have other heart problems such as an irregular heartbeat, or heart muscle changes.
Your heart may not pump blood around the body as well (cardiac failure), you may have inflammation of the outer lining of the heart and heart muscle. It is not known how often this happens with this treatment.
Symptoms of heart problems include chest pain that may feel like it is crushing and spreads to your arm, neck or jaw, tiredness, shortness of breath, heartbeat changes such as a pounding, racing or fluttering, feeling or being sick and sweating.
This treatment may cause of the . This can cause pain, discomfort, soreness, sores (ulcers) and bleeding.
It might include one or all of the following:
the throat
food pipe (oesophagitis)
the back passage (rectum)
Rarely you may have ulcers and bleeding in your stomach or bowel. You might also have inflammation of the bowel and a build up of gas within the bowel wall. It is not known how often these problems might happen.
Let your healthcare team know if you notice blood in your poo, have diarrhoea, bloating and tummy pain.
You can have painkillers to reduce the soreness. Taking painkillers about half an hour before meals to make eating easier. Your nurse, doctor or dietician will explain the best foods to have if you have any of these symptoms.
You might lose your appetite for various reasons while having cancer treatment. Sickness, taste changes or tiredness can put you off food and drinks.
You could lose all your hair. This includes your eyelashes, eyebrows, underarms, legs and sometimes pubic hair. Your hair will usually grow back once treatment has finished but it is likely to be softer. It may grow back a different colour or be curlier than before.
You might feel very tired and as though you lack energy.
Various things can help you to reduce tiredness and cope with it, for example exercise. Some research has shown that taking gentle exercise can give you more energy. It is important to balance exercise with resting.
The skin on your hands and feet may become sore, red, or may peel. You may also have tingling, numbness, pain and dryness. This is called hand-foot syndrome or palmar plantar syndrome.
Rarely your skin might develop an itchy raised bumpy rash. You might have skin colour changes such as redness on white skin. On black or brown skin areas may look darker than your normal skin tone. You may have general inflammation of the skin (dermatitis). This drug can also make your skin sensitive to sunlight. Patches of skin may get darker or lighter near veins.
Let your healthcare team know of any skin changes.
You might have liver changes that are usually mild and unlikely to cause symptoms. They usually go back to normal when treatment finishes. You have regular blood tests to check for any changes in the way your liver is working.
Speak to your doctor or nurse if you feel generally unwell after taking this drug.
These side effects happen in fewer than 1 in 100 people (less than 1%). You might have one or more of them. They include:
feeling happy and excited
eye problems - symptoms include rapid eye movement side to side, inflammation, blocked tear ducts, changes to vision, watery eyes and sensitivity to light
headaches
dizziness
shaking and trembling, stiffness and slow movement (symptoms of Parkinson's disease)
an unusual tightness or stiffness in the muscles
low blood pressure - you might feel dizzy, lightheaded or faint
nail problems including thickening, pain, infection, changes in colour of the nail and nail bed
sleepiness or difficult to stay awake (somnolence)
an allergic reaction that can cause a rash, shortness of breath, redness or swelling of the face and dizziness - some allergic reactions can be life threatening. Alert your nurse if you notice any of these symptoms
feeling confused and disorientated
changes in the brain - symptoms including problems with balance and body movements (ataxia), difficulty speaking, fits (seizures) and unable to wake up (coma)
a lack of blood getting to the brain, bowel, arms or legs
There isn't enough information to work out how often these side effects might happen. You might have one or more of them. They include:
slow wound healing
changes to the levels of chemicals in your blood due to the breakdown of tumour cells (tumour lysis syndrome) - you have regular blood tests to check for this
a rare disorder of the nerves causing headaches, fits, confusion and changes in vision - contact your healthcare team straight away. This condition is usually reversible
numbness or tingling in fingers or toes (peripheral neuropathy) is often temporary and can improve after you finish treatment
a high temperature
a build up of in the blood that can lead to damage
high level of a type of fat in the blood
low levels of vitamin B1 also known as thiamine in the body – this can be a medical emergency. Symptoms can include balance and coordination problems, making up memories that don’t exist, difficulty walking, drowsiness and heart problems
an injection site reaction – redness, darkening of the skin, pain, swelling may develop at site of injection – tell your nurse or doctor straight away if this happens
too much of a waste project called ammonia in the blood, this causes changes to the brain
We have more information about side effects and tips on how to cope with them.
Cancer drugs can interact with medicines, herbal products, and some food and drinks. We do not list these interactions on this page. An example is grapefruit or grapefruit juice which can increase the side effects of certain drugs.
Tell your healthcare team about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies. Also let them know if you have any other medical conditions or allergies.
You may not be able to become pregnant or get someone pregnant after treatment with this drug. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.
Men might be able to store sperm before starting treatment. And women might be able to store eggs or ovarian tissue. But these services are not available in every hospital, so you would need to ask your doctor about this.
This treatment may harm a baby developing in the womb. It is important not to become pregnant or get someone pregnant while you are having treatment.
Women must not become pregnant for at least 6 months after the end of treatment.
Men should not get someone pregnant for at least 3 months after treatment.
Talk to your doctor or nurse about effective contraception before starting treatment. Let them know straight away if you or your partner become pregnant while having treatment.
It is not known whether this drug comes through into the breast milk. Doctors usually advise that you don’t breastfeed during this treatment.
If you are having tests or treatment for anything else, always mention your cancer treatment. For example, if you are visiting your dentist.
Do not have live vaccines while you’re having treatment and for up to 12 months afterwards. For some people, it may be longer than this. The length of time you need to avoid live vaccines depends on the treatment you’ve had.
Ask your doctor or pharmacist how long you should avoid live vaccinations.
In the UK, live vaccines include rubella, mumps, measles, chickenpox, BCG, and yellow fever. You can usually have non-live vaccines. But they might not give you as much protection as usual. These include the:
flu vaccine, as an injection
coronavirus (COVID-19) vaccine
Talk to your doctor or pharmacist about the best time to have a vaccine in relation to your cancer treatment.
You can be in contact with other people who have had live vaccines as injections. If someone has had a live vaccine by mouth or nasal spray there may be a small risk the vaccine virus can be passed onto you if your is weakened.
Your healthcare team will let you know if you need to take any precautions if you are in close contact with someone who has had a live vaccine.
For further information about this treatment and possible side effects go to the electronic Medicines Compendium (eMC) website. You can find the patient information leaflet on this website.
You can report any side effect you have to the Medicines and Healthcare products Regulatory Agency (MHRA) as part of their Yellow Card Scheme.
Last reviewed: 05 Nov 2026
Next review due: 05 Nov 2029
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Having a DPD deficiency could make the side effects of the chemotherapy drugs fluorouracil and capecitabine worse.
