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A colonoscopy is a procedure that uses a long, narrow, flexible, telescopic camera called a colonoscope to look at the lining of your large bowel (colon and rectum). It tends to be done to find out more about any problematic symptoms you’re having or to check for signs of cancer. Sometimes, it’s used to confirm the results of other tests on your bowel, or as part of bowel cancer screening (see FAQs).

A colonoscopy can help your doctor to find out the cause of symptoms such as persistent diarrhoea or a change in your bowel habits. If you have bleeding or mucus coming from your back passage, it can look for problems that could be causing this. Or it may be used to find out more if you have unexplained pain in your abdomen (tummy) or feel tired and breathless.

A doctor or specialist nurse practitioner may carry out your colonoscopy – for simplicity we will refer to ‘doctor’ throughout. You’ll meet whoever is going to do your colonoscopy before it goes ahead so they can make sure you know what’s going to happen. It may not be exactly as we’ve described here as it will be adapted to suit you.

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Image showing where a colonoscope is passed


  • Preparation Preparing for a colonoscopy

    You’ll have a colonoscopy in hospital, usually as a day case. This means you have the test and go home the same day.

    Your hospital will advise you about how to prepare for your colonoscopy. The main thing that you need to do to prepare is to take a strong laxative – your hospital will arrange to give you this. Usually you will need to take a laxative a day before your colonoscopy but check this with your doctor. You need to take this laxative because it’s very important that your bowel is completely empty during the test. Otherwise your doctor may not be able to see it clearly.

    The laxative will give you diarrhoea, so you will need to stay close to a toilet. It’s also important to drink plenty of clear fluids to make sure you don’t get dehydrated. Clear fluids are those that don’t contain milk, such as water, squash and black tea and coffee – see our FAQs for more information. You may feel some pain or bloating in your abdomen (tummy) when you take a laxative. You might find the taste of the laxative unpleasant too.

    Before you have a colonoscopy you will also need to:

    • eat a low-fibre diet for a couple of days before the procedure – a day before your colonoscopy, just drink clear fluids
    • stop taking iron tablets – these make the inside of your bowel look black, which makes it hard for your doctor to see clearly
    • stop taking medicines that can affect the way your blood clots, such as warfarin, aspirin or clopidogrel, as well as painkillers such as ibuprofen

    If you take any medicines, check with your doctor if you need to stop taking them before having a colonoscopy.

    Your doctor will discuss with you what will happen before, during and after your procedure, and any pain you might have. You might like to prepare questions to ask about the risks, benefits and any alternatives to the procedure. This will help you to fully understand what’s involved, which is important so you can give your consent to have the procedure. You will be asked to do this by signing a consent form.

  • Alternatives What are the alternatives to a colonoscopy?

    A colonoscopy is usually the best investigation to show the inside of your bowel. However, it isn’t appropriate for everyone. If you can’t have a colonoscopy, your doctor may suggest other tests. The main alternatives are described below.

    • Barium enema. A fluid containing barium (a substance that shows up on X-rays) is passed through a tube that’s inserted into your anus and bowel. X-ray images of your abdomen (tummy) are taken, which show the inside of your bowel.
    • Virtual colonoscopy. This test involves having a CT scan of your abdomen after gas has been passed into your bowel to expand it. A CT scan uses X-rays to produce three-dimensional images of your large bowel and rectum.
    • Flexible sigmoidoscopy. This is a similar procedure to a colonoscopy but it uses a shorter instrument to look inside your rectum and the lower part of your large bowel.
  • The procedure What happens during a colonoscopy?

    The colonoscopy usually takes around 30 to 45 minutes.

    Your nurse will ask you to put on a hospital gown that opens at the back. You may be offered a sedative and a painkiller to help you to relax and be as comfortable as possible during the procedure.

    Your doctor will ask you to lie on your left-hand side and then will gently insert the colonoscope into your anus (back passage). They will use lubricating jelly to make this as easy as possible.

    Your doctor will pump air into your bowel through the colonoscope to expand it slightly and give a better view of your bowel. Your doctor will gently pass the colonoscope, which is flexible, through your bowel. The tip can be rotated so it follows the curves in your bowel.

    Image showing where a colonoscope is passed

    The images from the camera at the end of the colonoscope will appear on a monitor. During the procedure you may be asked to change your position – for example, to turn from your side on to your back. This will help your doctor to look at different areas of your bowel. They may press on your abdomen (tummy) to help move the colonoscope in the right direction too.

    Your doctor may take a biopsy or remove polyps (small growths on the lining of your bowel). Polyps are usually benign (not cancerous), but they can change into cancer over time. For more information, see our FAQs. If you have a biopsy, it will be done by passing instruments through the colonoscope and this is usually quick and painless. The samples will be sent to a laboratory for testing to see if the cells are benign or malignant (cancerous).

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  • Aftercare What to expect afterwards

    You’ll need to rest until the effects of the sedative have passed. After that you should be fine to go home when you feel ready but make sure someone can take you. And ask someone to stay with you for a day or so while the sedative wears off.

    Your doctor may discuss some findings from the colonoscopy with you before you leave, or you may be given a date for a follow-up appointment. If you’ve had a biopsy or polyps removed, your results will be sent to the doctor who referred you for the colonoscopy.

  • Recovery Recovering from a colonoscopy

    If you need pain relief, you can take over-the-counter medicines, such as paracetamol or ibuprofen. Always read the patient information leaflet that comes with your medicine and if you have any questions, ask your pharmacist for advice.

    Having sedation can leave you feeling sleepy. You might also find that you’re not so coordinated as usual or that it's difficult to think clearly. This should pass within 24 hours. In the meantime, don't drive, drink alcohol, operate machinery or sign anything important.

    Most people don’t have any problems after a colonoscopy but contact your GP or the hospital department straight away if you:

    • have heavy bleeding from your back passage
    • have a swollen abdomen (tummy) or pain in your abdomen that gets worse
    • feel weak, or develop a fever
  • Risks What are the risks?

    As with every procedure, there are some risks associated with colonoscopy. We haven’t included any statistics as it’s difficult to be exact because they vary for everyone. Ask your doctor to explain how the risks apply to you.


    These are the unwanted but mostly temporary effects you may get after having the procedure.

    After a colonoscopy, you may feel bloated and uncomfortable for an hour or so. You may find that massaging your abdomen and walking around helps to relieve this. You may also bleed a little from your back passage if you have had a biopsy or a polyp removed.


    Complications are when problems occur during or after the procedure. The main complications of a colonoscopy are listed below.

    • Your doctor may not be able to see your entire bowel. This can happen if it isn’t empty or the colonoscope can’t be passed round a curve. If this happens, you may need to have another colonoscopy or other tests.
    • You may have a reaction to the sedation, which can affect your breathing or your heart. But you will be monitored throughout the procedure and given treatment if this develops.
    • The colonoscope and the other instruments used during the procedure may damage or tear your bowel. If this happens, you may need an operation to repair it.
    • You may have heavy bleeding if you have had biopsies or polyps removed.
  • FAQs FAQs

    What are polyps and why do they have to be removed?


    Polyps are growths inside your bowel. They are quite common and usually don’t cause any problems. However, certain types of polyps can grow into cancers over time. If your doctor finds any polyps during your colonoscopy, he or she will probably remove them, or plan to remove them at a later date.


    Polyps are small, fleshy lumps, usually less than 1cm in size, although they can be bigger. About 30 in every 100 people develop a polyp in their lifetime, most often when they are over 40. Men are slightly more likely to develop polyps than women.

    Some polyps are attached to the side of your bowel on a stalk and look a bit like a mushroom. Others are flatter and have no stalk. You may have just one polyp, or several.

    Most polyps never cause any problems. However, there is a small chance that over time a type of polyp known as an adenoma will grow into a cancer. Most bowel cancers are thought to start as a polyp. So if your doctor finds any during your colonoscopy, they will want to remove them.

    Once your polyp is removed it doesn’t usually come back. But because you may develop new polyps, you may be advised to have regular colonoscopies. How often you have these will depend on how many polyps you have had and when a polyp was last found.

    What should I eat and drink before a colonoscopy?


    Your doctor will ask you to eat low-fibre foods for two days before your colonoscopy. The day before the procedure you will need to only drink clear liquids. This is to make sure your bowel is empty so that your doctor can see it clearly during the test.


    A colonoscopy is a procedure that allows your doctor to look inside your large bowel. In order for your doctor to see it clearly, it needs to be completely empty. For this to happen you’ll need to change what you eat and drink in the days before your procedure.

    Your doctor will ask you not to eat any high-fibre foods for two days before your colonoscopy. High-fibre foods include most fruit and vegetables, wholemeal bread and pasta, brown rice, pulses and nuts. Instead, stick to low-fibre foods such as lean meat, fish, boiled potatoes without the skin on and white bread, pasta and rice. You’ll also need to drink clear fluids only. This means fluids such as water, squash, clear soup, meat extract drinks, tea and coffee (without milk).

    The day before your colonoscopy you will need to stop eating solid foods and have only clear fluids.

    You will receive full instructions from your hospital before your colonoscopy appointment. It’s important to follow these carefully.

    Will I need to have a colonoscopy as part of screening for bowel cancer?


    Bowel cancer screening aims to find cancer when it’s in the early stages. If blood is found in your faeces during screening, you may be offered a colonoscopy to look at the inside of your bowel.


    If bowel cancer is found early, treatment is more likely to be effective. Screening is offered to everybody between 60 and 69 in England and this age range is currently being extended to 74. The age range differs slightly in other parts of the UK.

    If you’re eligible for screening, you will be offered a test every two years.

    Everyone is offered a test called faecal occult blood (FOB) testing. This checks for blood in your faeces (one of the possible signs of bowel cancer). You’ll be sent a testing kit and instructions on how to take a sample of faeces. You send this to a laboratory and should usually get the results back within two weeks.

    Out of every 100 people who do the test, about 98 have a normal result. If you have an unclear or abnormal result, blood may have been found in your faeces. You’ll be offered more tests to find out what is causing this and one of these is a colonoscopy. Remember you may have blood in your faeces because of conditions other than cancer.

    In addition to standard screening, people in some parts of the country are now being offered bowel scope screening. You have this, only once, at the age of 55. This test, called a flexible sigmoidoscopy, is quicker than a colonoscopy. It only examines the last part of your large bowel rather than all of it.

    If you would like more information about bowel cancer screening, contact your GP or nurse.

  • Resources Resources

    Further information


    • Colorectal cancer. National Institute for Health and Care Excellence (NICE), December 2014.
    • Colon cancer. National Comprehensive Cancer Network., published 2014
    • Colonoscopy. Medscape., published 20 March 2014
    • Having a colonoscopy. NHS Screening Programmes., published March 2013
    • Colorectal cancer. BMJ Best Practice., published 19 December 2013
    • Map of Medicine. Colorectal cancer. International view. London: Map of Medicine; 2014 (issue 4)
    • Map of Medicine. Crohn’s disease. International view. London: Map of Medicine; 2014 (issue 1)
    • Colonic polyps. Medscape., published 18 October 2014
    • Colonoscopy. National Digestive Diseases Information Clearinghouse., published September 2013
    • Bowel cancer screening: the facts. NHS Screening Programmes., published September 2012
    • Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press., accessed 9 December 2014
    • Colonoscopy. Bowel Screening Wales., accessed 9 December 2014
    • Quality standard for colorectal cancer. National Institute for Health and Care Excellence (NICE)., published August 2012
    • Bowel cancer. British Society of Gastroenterology., accessed 9 December 2014
    • Computed tomographic colonography (virtual colonoscopy). National Institute for Health and Care Excellence (NICE), June 2005.
    • Colonoscopy. Beating Bowel Cancer., published 13 February 2014
    • Colonoscopy tests for bowel cancer. Macmillan., published 1 January 2013
    • Polyps of the colon and rectum. American Society of Colon and Rectal Surgeons., published 2012
    • Dietary fibre. British Nutrition Foundation., published 26 June 2014
    • Overview of the NI bowel cancer screening programme. Public Health Agency., accessed 9 December 2014
    • About the screening programme. NHS Scotland., accessed 9 December 2014
    • Key messages about the screening programme. Public Health Wales., accessed 9 December 2014
    • Bowel scope screening. NHS Bowel Cancer Screening Programme., published January 2013
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