Digestion problems

Cancer or its treatment can cause digestion problems such as constipation, diarrhoea, sickness (nausea) and sometimes a blocked bowel (obstruction).


Constipation means having difficulty going for a poo (stool, bowel movement). You might not have one for a few days or more. Knowing what is normal for you will help you know whether you have constipation or not.  

There are several causes of constipation in people with cancer. One cause is when cancer grows in the bowel and blocks it. This is also called a bowel obstruction. Not eating and drinking enough can also lead to constipation.

Other causes are some drugs used in cancer treatment. These include:

  • painkillers such as opioids
  • some chemotherapy drugs
  • some anti sickness drugs

Constipation can make you feel full, and you may not want to eat. This can cause weight loss.

Your doctor or nurse will give you mild laxatives to take while you have any treatments that can cause constipation. Tell your doctor or nurse if your constipation lasts for more than 3 days.

Constipation is easier to sort out if your doctor treats it early. It may also help to drink plenty of fluids and eat as much fresh fruit and vegetables as you can. If you cannot manage the food, do not worry too much, but make sure you do drink.


Diarrhoea usually means having more than 3 unformed poos (stools, bowel movements) in 24 hours. It is a common side effect of some cancer drugs such as:

  • chemotherapy
  • targeted cancer drugs
  • immunotherapy

Radiotherapy for some types of cancer can also cause diarrhoea.  

Diarrhoea usually disappears a few days after treatment, but it may go on for some weeks after treatment. It's not only unpleasant but can also make you feel weak and tired. And if it is severe, it may lead to weight loss and malnutrition, and affect your quality of life.

With diarrhoea, it is easy to become dehydrated and lose some of the salts (electrolytes) in your body. So try to drink plenty of fluids. Talk to your doctor if you can't drink enough or think you are losing more fluid than you can replace. If you have diarrhoea after any treatments, tell your doctor or nurse. They can give you tablets to take with your next lot of treatment to reduce the diarrhoea.

You can also ask about soothing creams to apply around your anus. Severe diarrhoea can make the skin in this area get very sore and sometimes break down.

Call your hospital advice line straight away if you have diarrhoea after immunotherapy as this can be serious.

Sickness (nausea)

Sickness is the unpleasant feeling in the back of your throat and your stomach that you want to be sick (vomit).

Sickness or being sick warns and protects the body against something that shouldn't be there.

In people with cancer, there are several causes of sickness. It is a common side effect of cancer drugs such as some:

  • chemotherapy drugs
  • hormone therapies
  • targeted cancer drugs
  • immunotherapies
  • bisphosphonates
  • painkillers

Other causes of sickness include:

  • a blocked bowel
  • changes to certain chemicals in the blood
  • cancer that has spread to the brain

Feeling and being sick can interfere with eating and drinking and digesting food. This can cause problems like:

  • loss of appetite
  • weight loss
  • fluid changes in your body which can lead to dehydration
  • fatigue
  • disruption to your daily life

All these problems can affect your quality of life. Talk to your doctor or nurse if you are feeling sick. They can suggest several drugs to relieve your symptoms.

A blocked bowel

Sometimes cancer in the tummy (abdominal) area can grow so that it partly or completely blocks the bowel.

This is called a bowel obstruction. The waste from the food you have digested can't get past the blockage.

This can cause symptoms such as:

  • feeling bloated and full
  • loss of appetite
  • tummy (abdominal) pain which can be crampy
  • feeling sick
  • vomiting large amounts
  • constipation
  • a hard tummy (abdomen)
  • bleeding from the back passage when the blockage is in the large bowel

All these symptoms can make eating and drinking difficult and lead to weight loss.

  • Cancer and its management (7th edition)
    Tobias J and Hochhauser D
    Wiley-Blackwell, 2015

  • Managing Constipation in Adults With Cancer

    R Wickham

    Journal of the Advanced Practitioner in Oncology. 2017 March; 8(2): 149–161

  • Constipation

    BMJ Best Practice

    Accessed March 2020

  • Variations in the management of diarrhoea induced by cancer therapy: results from an international, cross-sectional survey among European oncologists

    M Kordes and M Gerling

    ESMO Open. 2019; 4(6): e000607

  • The Royal Marsden Manual of Clinical Nursing Procedures, 9th edition

    L Dougherty and S Lister (Editors)

    Wiley-Blackwell, 2015 

  • Nausea: a review of pathophysiology and therapeutics

    P Singh and others

    Therapeutic Advances in Gastroenterology 2016 January; 9(1): 98–112

  • 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 patientinformation@cancer.org.uk with details of the particular issue you are interested in.

Last reviewed: 
18 Mar 2020
Next review due: 
20 Mar 2023

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