Your mouth and cancer drugs

Some cancer drugs can cause a sore or dry mouth. But some treatments can help, and there are things you can do to cope.

How cancer drugs can affect your mouth

Doctors use many different types of drugs to treat cancer. Some drugs can change the cells in the lining of your mouth and make it sore (mucositis). Other drugs may affect the secretion of spit (saliva) in your mouth, causing a dry mouth (xerostomia) or taste changes.

Even if a drug can cause these 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. It depends 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

Soreness and mouth ulcers


Mucositis means inflammation of the lining 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 kill not only the quickly dividing cancer cells but also the cells that make up the lining of your mouth. These cells also divide quickly.

Mucositis can be painful, and you might find it hard to eat and drink. Some people find that it affects their quality of life. Your mouth might be more painful if you’re having high dose chemotherapy.

A sore mouth affects about 20 to 40 out of every 100 people (20 to 40%) having chemotherapy. And about 80 out of every 100 people (80%) having high dose chemotherapy for stem cell transplants.

Targeted cancer drugs and immunotherapy can also cause a sore mouth. 

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.


It is important to keep your mouth clean 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 mouth ulcers can get infected. But 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.

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.

Tips for mouth care

  • 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.
  • 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 – mix one teaspoon of salt in one glass of tepid water (don’t swallow it).

Tips for eating with a sore mouth

  • 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.

A dry mouth

Some cancer drugs can make your mouth dry. This is also called xerostomia. It happens because the drugs affect the spit glands (saliva).

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 will improve 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.

Tips for 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 chips 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.

More information

There are many ways your team can help you with a sore mouth and other mouth problems.

  • Cancer: Principles and Practice of Oncology (12th edition)
    VT DeVita, TS Lawrence, SA Rosenberg
    Wolters Kluwer, 2023

  • Oral toxicity associated with systemic anticancer therapy

    R Negrin and others

    UpToDate website

    Accessed May 2023

  • Electronic Medicines Compendium
    Accessed May 2023

  • Scenario: Oral pain
    National Institute of Health and Care Excellence (NICE) - Clinical Knowledge Summaries, December 2022

    Accessed May 2023

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. If you need additional references for this information please contact with details of the particular issue you are interested in.

Last reviewed: 
31 May 2023
Next review due: 
31 May 2026

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