Chemotherapy side effects: digestion

Some chemotherapy drugs can affect the lining of the digestive system and may cause various problems.

Sore mouth

When symptoms may occur: 7–14 days after chemotherapy

Symptoms include:

  • Dry mouth and tongue
  • Sore mouth or tongue
  • Bleeding from gums
  • Mouth or tongue

What you should do:

  • Drink plenty of fluids
  • Use a mouth wash regularly
  • Clean your teeth regularly
  • Keep your lips moist
  • Contact your GP or hospital immediately if you are unable to eat or drink because of mouth ulcers

During chemotherapy the lining of your mouth may become sore and prone to infection. This usually happens around 7 to 10 days after chemotherapy. It’s important that you keep your mouth clean and healthy, and the following suggestions may help:

  • Drink plenty of fluids, to keep your mouth moist and fresh.
  • Use a mouthwash regularly. Ask your doctor, nurse or oral hygienist which one is best.
  • Clean your teeth regularly using fluoride toothpaste and a soft toothbrush. If someone needs to clean your teeth for you, they may find a child’s toothbrush easier to use.
  • Clean your dentures after meals as well as at night.
  • Keep your lips moist using a lip salve available from a chemist.

Tell your doctor or nurse if your mouth becomes sore. It may be possible to prescribe some tablets to prevent this in future. If you need further advice, ask to see an oral hygienist. Depending on the cause of your sore mouth it may be possible to provide you with medication to relieve the discomfort.

During chemotherapy, you may be more prone to infection and bleeding. Always consult your doctor before having any dental work done. Your blood count may need to be checked before the dentist can decide whether to proceed with dental treatment or not.

Taste and smell changes

Possible side effect:

  • Taste changes
  • Changes in smell

When symptoms may occur: during your course of chemotherapy

Symptoms include:

  • Changes in the way food or drink taste
  • Increased awareness of smells that may now become unpleasant, for example cooking and perfumes

What you should do:

  • Suck a strong flavoured sweet if you have an unpleasant taste during an injection
  • Avoid areas where unpleasant smells are present

Some people experience a change in their sense of taste or smell. You may find that food may taste more salty, bitter or metallic. This is only temporary. Normal taste and smell usually returns two or three months after the end of treatment.

If an unpleasant taste occurs during an injection, it can be disguised by a strong-flavoured sweet.

Occasionally, some people may experience food cravings.

Find out more about eating well when you have cancer.

Nausea and vomiting

Possible side effect: Nausea and vomiting

When symptoms may occur: 7-14 days after chemotherapy

Symptoms include:

  • Feeling sick (nausea)
  • Being sick (vomiting)

What you should do:

  • You should take anti-sickness tablets or suppositories regularly as prescribed
  • Contact your hospital if you continue to have nausea or vomiting – you can be given different anti-sickness drugs that may be more effective

Nausea and vomiting aren't side effects of every chemotherapy drug although many people believe they are. Some drugs or treatment plans cause a greater reaction than others. Also, everyone is individual – a similar drug combination may cause nausea in one person but not in another.

If you do feel nauseous or even vomit following your treatment, there are many anti-sickness (anti-emetic) drugs to help overcome this problem. These come as tablets, injections or suppositories.

You will be given anti-sickness injections before the chemotherapy and tablets to take home with you. You should take these regularly as prescribed, even if you are not feeling sick, as some anti-sickness drugs are better at preventing than stopping sickness. Some people find taking ginger helpful.

Should you still have nausea or vomiting, please tell your doctor or nurse and you can be given different anti-sickness drugs that may be more effective. If you experience vomiting at home then anti-sickness tablets may not be effective and you should ask your doctor for suppositories with your next course.

You may also find relaxation or other therapy helpful.

Watch our video about how to manage nausea during chemotherapy.

Changes in appetite

When symptoms may occur: 7-14 days after chemotherapy

Symptoms include: You may not feel like drinking or eating

What you should do:

  • Drink plenty of fluids
  • Have small frequent meals or snacks
  • Ask to see a dietitian if you are worried about your diet

If you experience any taste changes or lose your appetite, you may not feel like drinking or eating. However, you should try to drink plenty of fluids (about ten glasses or cups each day) and eat well.

Try sipping clear, cold fluids, such as water and soft drinks, slowly through a straw. Fizzy drinks like soda water and ginger ale are quite refreshing, as are lemon or herbal teas. Avoid coffee, which has a strong taste and may also make you more thirsty.

You may need to change your meal times and have small, frequent meals or snacks of whatever you fancy. Eat slowly and chew your food well. After a meal, relax in a sitting or slightly reclined position instead of lying down. Eat light meals on the day of your treatment.

Find out more about eating well when you have cancer. If you’re worried at all about your diet, please ask to see a dietitian.

Diarrhoea or constipation

When symptoms may occur: 7-14 days after chemotherapy

Symptoms include:

  • Frequent or loose bowel movements
  • Not be able to control bowel action
  • Irregular or hard bowel movement

What you should do: 

  • Drink plenty of fluids
  • Contact your GP or hospital immediately if you have diarrhoea (four or more bowel movements more than usual or diarrhoea at night)

Diarrhoea or constipation may occur with a few drugs. They can often be managed by tablets, medicines or a change of diet. Please tell your doctor or nurse if you have any problems.

Watch our video about how to manage constipation during chemotherapy.