Side effects of cancer drugs
Doctors use many different types of drugs to treat cancer. Some drugs can change the cells in the lining of your causing inflammation and soreness. This is called mucositis.
This information is about mucositis in your mouth. The mouth is the start of your digestive system. This is also known as stomatitis.
Some cancer drugs can affect the amount of spit (saliva) made in your mouth. This causes a dry mouth (xerostomia) or taste change
Find out more about taste changes
Even if a drug can cause these side effects, it may not affect you that way. Drugs affect people in different ways, and it is not possible to tell in advance who will have side effects or how severe they will get it. Mouth side effects can depend on:
the drug or combination of drugs you are having
the dose
the route (by mouth or as an injection or a drip through a vein)
how you react to the drug
how you reacted to drug treatment in the past
Read more about cancer drugs and their side effects
Oral mucositis means inflammation of the lining (mucus membrane) of the mouth. The inside of your mouth might become red and swollen with white patches. These areas can turn into ulcers.
A sore mouth happens because some cancer drugs work by killing cancer cells or stopping them from growing. But they also usually affect some healthy cells too. These cells make up the lining of your mouth.
Oral mucositis is painful, and you might find it hard to eat and drink. Some people find that it affects their . Your mouth might be more painful if you’re having high dose chemotherapy.
Oral mucositis affects about 20 to 40 out of every 100 people (20 to 40%) having chemotherapy. If your having high dose chemotherapy for a oral mucositis affects up to 80 out of every 100 people (up to 80%).
and can also cause oral mucositis. How often you might get oral mucositis from targeted cancer drugs varies and depends on how the drugs work. For example, oral mucositis happens in about 30 to 40 out of every 100 people (30 to 40%) in people taking sunitinib, sorafenib, lenvatinib or regorafenib. But this is different to other targeted drugs.
A type of immunotherapy called can also cause mucositis, but it happens less often. It can also happen months after you had the treatment.
A sore mouth caused by chemotherapy usually happens about 7 days after you start treatment and is at its worst around days 10 to 14. It gradually clears up about 2 weeks after it started.
Bisphosphonates and hormone therapies do not usually cause a sore mouth.
Treatment for oral mucositis is based on the symptoms you are experiencing.
To help prevent and lessen the severity of the mucositis it is important to keep your mouth clean and moist while having cancer drugs. You should particularly do so if you have drugs known to cause mouth ulcers. Your doctor or nurse might give you mouthwashes to help prevent infection. You have to use these regularly to get the most protection.
Sometimes you can get an infection in the mouth, your doctor or specialist nurse can give you treatment for this.
Tell your doctor or nurse straight away if your mouth is sore. They can offer advice and treatment to help your mouth be less sore. You might need strong painkillers such as morphine or morphine based painkillers. This will help control mouth pain, and eating and drinking will be more comfortable. You might be able to have numbing mouth rinse or spray.
When you're having high dose chemotherapy and radiotherapy before a stem cell transplant, you are likely to get a sore mouth. Your doctor can prescribe medicines to help prevent soreness.
Find out more about keeping your mouth healthy
Check your mouth daily for changes.
Brush your teeth with a soft toothbrush at least twice a day and preferably after every meal and at bedtime.
Talk to your doctor or nurse about flossing.
Rinse your mouth after every meal to get rid of food on your teeth. Avoid mouthwashes that contain alcohol.
Eat soft, moist foods and avoid food and drinks that irritate your mouth including alcohol.
Use lip balm to keep your lips moist.
Use a salt-water mouthwash to rinse your mouth – mix one teaspoon of salt in one glass of tepid water (don’t swallow it).
Avoid neat spirits, fizzy drinks, tobacco, hot spices, garlic, onion, vinegar and salty food.
Crispy or hard foods like bread rolls, crispbread, such as Ryvita, or potato crisps can irritate your mouth.
Moisten meals with gravies and sauces to make swallowing easier.
Let food cool down before eating or eat cold foods.
Try to drink at least one and a half litres (3 pints) of fluid a day – have tea or coffee, some fruit and vegetable juices, soft drinks or water.
Tell your doctor or nurse if you have mouth ulcers.
Avoid acidic fruits such as oranges, grapefruit, lemons or tomatoes.
Chew sugar free gum to help you to produce more saliva to keep your mouth moist.
Some cancer drugs can make your mouth dry. This is also called xerostomia (pronounced zero-stow-mee-a). It can happen because the drugs affect the spit glands (salivary glands).
Your spit might be thick and make swallowing and talking difficult. In some people, it can be more of a problem than others. A dry mouth usually improves once you’ve finished treatment.
Cancer drugs that can cause a dry mouth are some types of:
chemotherapy
immunotherapy
anti sickness
painkillers
The following tips might help to cope with the symptoms of a dry mouth.
Keep a drink available that you can sip.
Chew sugar free gum or suck on sugar free sweets.
Try to drink at least 3 pints (one and a half litres) of fluid a day.
Choose meals that are moist.
Use gravies and sauces to make swallowing easier.
Milk, water, fruit or vegetable juices are the best drinks to choose, but any fluid is better than nothing.
Suck ice cubes or ice lollies to refresh your mouth.
Eating fresh or tinned pineapple can keep your mouth fresh and moist, but avoid acidic fruits (such as oranges, grapefruit) if your mouth is sore.
If you want to drink citrus juices, dilute them with water so they are not as acidic.
If your mouth is very dry talk to your doctor or nurse about artificial saliva products – they are available as tablets, mouthwashes, gum, pastilles, gels, sprays and toothpastes.
Keep your lips moist with a lip balm.
Avoid alcohol, tobacco, caffeine and dry or hard to chew foods.
Do regular mouth care.
There are many ways your team can help you with a sore mouth and other mouth problems.
Last reviewed: 12 Aug 2026
Next review due: 12 Aug 2029
There are different cancers and treatments that cause mouth problems, and different ways of treating them.
Cancer and its treatment can cause eating and drinking difficulties in some people. But there are people that can help and things you can do to cope better.
Cancer drugs have side effects and these can vary from person to person. But there are things that you can do to help you cope.
There are many different types of cancer drugs. Some treat cancer, and others help to relieve symptoms such as sickness and pain. The type of drugs you need for your cancer depends on what type of cancer you have.
Treatments can include surgery, radiotherapy and drug treatments (such as chemotherapy, hormone therapy or targeted cancer drugs). Find out about treatments and how to cope with side effects.
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