Digestion problems

Cancer and 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 a poo for a few days or more
  • have hard or lumpy poo
  • have to strain or find it difficult to open your bowels

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.

Some drugs used in cancer treatment can also cause constipation. 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.

Tell your healthcare team if think you are constipated. Your doctor or nurse can give you mild laxatives to take while you have any treatments that can cause constipation.

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 can't manage food, don't worry too much, but make sure you do drink.


Diarrhoea means passing frequent loose poo (stool, bowel movement). It is a common side effect of some cancer drugs such as:

  • chemotherapy
  • targeted cancer drugs
  • immunotherapy

Radiotherapy and surgery for some types of cancer can also cause diarrhoea.  

Diarrhoea usually disappears a few days after treatment, but it may go on for some time. If you have diarrhoea after any treatments, tell your healthcare team. They can give you tablets to take with your next lot of treatment.

Diarrhoea isn’t 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. 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.

You can also ask about soothing creams to apply around your back passage (anus). Severe diarrhoea can make the skin in this area 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).

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

  • chemotherapy drugs
  • hormone therapies
  • targeted cancer drugs
  • immunotherapies
  • bisphosphonates
  • surgery
  • radiotherapy treatments
  • painkillers

Other causes of sickness include:

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

Feeling and being sick can interfere with eating, 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 healthcare team if you are feeling sick. They can suggest several drugs to relieve your symptoms.

A blocked bowel (bowel obstruction)

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 pain which can be crampy
  • feeling sick
  • vomiting large amounts
  • constipation
  • a hard tummy
  • 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)
    J Tobias and D Hochhauser
    Wiley-Blackwell, 2015

  • The Royal Marsden Manual of Clinical and Cancer Nursing Procedures (10th edition, online)
    S Lister, J Hofland and H Grafton 
    Wiley Blackwell, 2020

  • Tips to help with eating problems after critical illness
    The Association of UK Dietitians, 2020

  • ESPEN expert group recommendations for action against cancer-related malnutrition
    J Arends and others
    Clinical Nutrition, 2017. Volume 36. Pages 1187-1196

  • Diagnosis, assessment and management of constipation in advanced cancer: ESMO clinical practice guidelines
    PJ Larkin and others
    Annals of Oncology, 2018. Volume 29. Pages iv111-iv125

  • 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: 
13 Sep 2023
Next review due: 
14 Sep 2026

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