We explain the most common side effects of 5FU here. But we don’t include all the rare ones that are unlikely to affect you.
You may get some of the side effects we mention but you are very unlikely to get all of them. If you are having other chemotherapy drugs as well, you may have some side effects that we don’t list here. Always tell your doctor or nurse about the side effects you have.
Your doctor can prescribe drugs to help control some side effects. It is very important to take them exactly as your nurse or pharmacist has explained. This means they will be more likely to work better for you. Your nurse will give you advice about managing your side effects. After your treatment is over, the side effects will start to improve.
Serious and life threatening side effects
Sometimes cancer drugs can result in very serious side effects, which rarely may be life threatening. Your cancer doctor and nurse can explain the risk of these side effects to you.
Contact the hospital
Your nurse will give you telephone numbers for the hospital. You can call them if you feel unwell or need advice any time of day or night. Save these numbers in your phone or keep them somewhere safe.
More information about this drug
We are not able to list every side effect for this treatment here, particularly the rarer ones. For more detailed information you can visit the electronic Medicines Compendium (eMC).
Risk of infection
5FU can reduce the number of white blood cells in your blood. This will make you more likely to get an infection. When the number of white blood cells is low, it’s called neutropenia.
Contact the hospital straight away on the contact number you’ve been given if:
- your temperature goes over 37.5°C (99.5°F)
- you suddenly feel unwell, even with a normal temperature
- you have symptoms of an infection.
Symptoms of an infection include:
- feeling shivery
- a sore throat
- a cough
- diarrhoea
- needing to pass urine often.
The number of white blood cells will usually steadily increase and return to normal before your next treatment. You will have a blood test before having more chemotherapy. If your white blood cells are still low, your doctor may reduce the dose of your chemotherapy or delay your treatment for a short time.
Bruising and bleeding
5FU can reduce the number of platelets in your blood. Platelets are cells that help the blood to clot. Tell your doctor if you have any bruising or bleeding you can’t explain. Bruising and bleeding includes:
- nosebleeds
- bleeding gums
- blood spots
- rashes on the skin.
Some people may need a drip to give them extra platelets.
Anaemia (low number of red blood cells)
5FU can reduce the number of red blood cells in your blood. These cells carry oxygen around the body. If the number of red blood cells is low, you may be tired and breathless. Tell your doctor or nurse if you feel like this. If you are very anaemic, you may need a drip to give you extra red blood cells (blood transfusion).
Feeling sick or being sick
This may happen in the first few days after chemotherapy. Your doctor will prescribe anti-sickness (anti-emetic) drugs to help prevent or control sickness. Take the drugs exactly as your nurse or pharmacist explains to you. It’s easier to prevent sickness than to treat it after it has started.
If you still feel sick or are vomiting, contact the hospital as soon as possible. They can give you advice and change the anti-sickness drug to one that works better for you.
Diarrhoea
This can sometimes be severe. Your doctor can prescribe anti-diarrhoea drugs to control it. You may be given these before you leave hospital. It’s important to take them exactly as your nurse or pharmacist explains. Make sure you drink at least two litres (three and a half pints) of fluids every day if you have diarrhoea. If you have diarrhoea for more than 4 to 6 times a day, or at night, contact the hospital straight away on the numbers your nurse gave you.
Sore mouth
Your mouth may become sore and you may get ulcers. This can make you more likely to get an infection in your mouth. Gently clean your teeth and/or dentures morning and night and after meals. Use a soft-bristled or children’s toothbrush. Your nurse might ask you to rinse your mouth regularly or use mouthwashes. It’s important to follow any advice you are given and to drink plenty of fluids.
Tell your nurse or doctor if you have any problems with your mouth. They can prescribe medicines to prevent or treat mouth infections and reduce any soreness.
Loss of appetite
You may lose your appetite during your treatment. Try to eat small meals regularly. Don’t worry if you don’t eat much for a day or two. If your appetite doesn’t improve after a few days, let your nurse or dietitian know. They can give you advice on getting more calories and protein in your diet. They may give you food supplements or meal replacement drinks to try. Your doctor can prescribe some of these and you can buy them from chemists.
Taste change
You may get a bitter or metallic taste in your mouth or find that food tastes different. This should go away when your treatment finishes. Try using herbs and spices (unless you have a sore mouth or ulcers) or strong-flavoured sauces to give your food more flavour. Sucking boiled sweets can sometimes help get rid of a bitter or metallic taste. Your nurse can give you more advice.
Tiredness
Feeling very tired is a common side effect. It’s often worse towards the end of treatment and for some weeks after. Try to pace yourself and get as much rest as you need. It helps to balance this with some gentle exercise, such as short walks. If you feel sleepy, do not drive or operate machinery.
Soreness and redness of palms of hands and soles of feet
This is called palmar-plantar or hand-foot syndrome. It gets better when treatment ends. Your doctor or nurse can give you advice and prescribe creams to improve the symptoms. It can help to keep your hands and feet cool and to avoid tight-fitting socks, shoes and gloves.
Hair loss
Your hair may thin but you’re unlikely to lose all the hair from your head. This usually starts after your first or second cycle of chemotherapy. It is almost always temporary and your hair will grow back after treatment ends. Your nurse can give you advice about coping with hair loss.
Changes in the way the heart works
5FU can affect the way the heart works. You may have tests to see how well your heart is working before, during and sometimes after treatment.
If you have pain or tightness in your chest, feel breathless or notice changes to your heartbeat at any time during or after treatment, tell a doctor straight away. These symptoms can be caused by other conditions but it’s important to get them checked by a doctor.
