If you have symptoms such as persistent diarrhoea or a change in your bowel habits, or bleeding or mucus coming from your back passage, your doctor may recommend a test called a colonoscopy. A colonoscopy allows a closer look inside your large intestine (rectum and colon) to find out what is causing your symptoms.

Colonoscopy is the examination of the bowel with a flexible video ‘telescope’. It is carried out to investigate bleeding from the rectum (back passage), changes in bowel movements, abdominal pain and other abnormalities, to check for disease and to look for polyps (small growths on the wall of the bowel).

Schematic picture of a colonoscopy

Before the Examination

  • You will be given laxatives to take at set times on the day before the examination, and you should drink only clear fluids (water, black tea or coffee, or squash) to help clean the bowel and avoid dehydration.
  • It is important that the bowel is clean and empty before a colonoscopy. If the bowel is not properly prepared it can be difficult to see the bowel lining clearly and problems may be missed, so follow instructions carefully. If the findings are unclear, the procedure may have to be repeated.
  • You will have the option of sedation, given as an injection or gas and air, or you can choose to remain unsedated. If you have a sedative you will feel drowsy but remain conscious. You may feel drowsy and/or unsteady for up to 24 hours, so it is important to have someone to help you home after the procedure, and you should not drive or carry out any activity that could be compromised by a lack of attention.

The Procedure

For the colonoscopy, you will be asked to lie on your side with your legs drawn up toward your chest. You may be asked to change position during the procedure; the endoscopist and nurse will help you.

  • The tube is passed into the bowel through your rectum. Some air will be blown into the bowel to improve the view of the bowel wall. This can make you want to pass wind, and you will be encouraged to do so to reduce any discomfort. Doctors and nurses are used to this, so don’t worry.
  • The examination is usually performed as an outpatient procedure, and typically lasts 15–30 minutes.
  • Occasionally, small pieces of tissue may be removed painlessly (biopsy) by the colonoscope for more detailed examination in the laboratory. Results are usually available in 1–2 weeks. Polyps can also be removed using this procedure.


First published on: embarrassingproblems.com
Reviewed and edited by: Dr Kevin Barrett
Last updated: October 2020

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