Expert reviewer, Mr Stephen Pollard, Consultant Surgeon
Next review due June 2020

A colonoscopy is a test that uses a narrow, flexible, telescopic camera called a colonoscope to look at the lining of your large bowel.

A colonoscopy can be used to detect irritated and swollen tissue, ulcers, or growths such as polyps. It helps to diagnose health conditions like Crohn’s disease, ulcerative colitis, diverticular disease and bowel cancer.

An older couple walking their dog in the woods

About a colonoscopy

You’ll have a colonoscopy as part of the national bowel cancer screening programme, or because you have bowel symptoms that your doctor needs to investigate. Using the colonoscope is a good way to do this because the camera can see directly any irritated tissue or growths in the lining of your large bowel.

Your large bowel is the last part of your digestive system, and consists of your bowel and rectum. Your rectum connects your bowel to your anus. The illustration above shows where a colonoscope is passed.

A doctor or specialist nurse practitioner may do your colonoscopy procedure but for simplicity, we’ll refer to your ‘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. Your care may be different from what’s described here as it will be adapted to meet your needs.

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 give you some instructions on how to prepare for your colonoscopy. It may be possible to choose where you have your procedure. You might be told about units with a JAG accreditation, if this is an option for you. This comes from The Joint Advisory Group on Gastrointestinal Endoscopy (JAG), which is part of the Royal College of Physicians. If you’d like to find out more, visit their website for further information.

To enable your doctor to see everything clearly, your bowel will need to be completely empty for the procedure. Your hospital will give you a strong laxative that you’ll need to take the day or evening before your colonoscopy – but check the instructions. The laxative usually comes as a powder that you mix with water.

The laxative will give you diarrhoea, so make sure you stay close to a toilet after you take it. Drink plenty of clear fluids like water, squash or black tea or coffee to make sure you don’t get dehydrated. For more information, see our FAQ: Eating and drinking beforehand. You might feel some discomfort or bloating in your tummy (abdomen) when you take a laxative, and it can taste unpleasant. It might taste better if you put the mixture in the fridge before you drink it. Remember that although taking a laxative isn’t very nice, it’s really important for the test to go well.

Before you have a colonoscopy you’ll also need to:

  • eat a low-fibre diet for a couple of days before the procedure, and then switch to only clear fluids the day before
  • if you take iron tablets, stop the week before your colonoscopy  because they make the inside of your bowel black; this makes it difficult to see clearly
  • stop taking any medicines that affect the way your blood clots (e.g. warfarin, aspirin or clopidogrel) as well as painkillers such as ibuprofen

If you take any of these medicines (or any others), let your hospital know before you have the colonoscopy. They can check if you need to stop taking them, and for how long. If you have a health condition, such as diabetes, let your hospital know as the preparation might be different for you. Your hospital will give you all the information you need.

Your doctor will already have gone through everything in detail before you get to the point where you go to hospital for your colonoscopy. They’ll also have given you the opportunity to ask questions about the risks, benefits and alternatives to the procedure. Once you get to hospital, they’ll go over what will happen before, during and after your procedure, and any pain you might have. So you should have all the information you need to give your consent for the colonoscopy to go ahead. You’ll be asked to sign a consent form beforehand.

What are the alternatives to a colonoscopy?

A colonoscopy is usually the best investigation to show the inside of your bowel. But it isn’t appropriate for everyone so your doctor might suggest other tests. Other options include the following.

  • 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 similar to a colonoscopy but uses a shorter instrument to look inside your rectum and the lower part of your large bowel only.
  • Barium enema. This involves placing fluid that contains barium (a substance that shows up on X-rays) into your bowel via your anus. The fluid coats the inside of your bowel, which gives clearer X-ray images.

What happens during a colonoscopy?

A colonoscopy usually takes around half an hour to an hour.

Your nurse will ask you to put on a hospital gown that opens at the back and lie on an exam table. You may be offered a sedative and a painkiller to help you to relax and be as comfortable as possible during the procedure. The sedative will be given to you as an injection into a vein in your hand. Depending on which medicine you have, and how much, it might make you feel sleepy and you might not remember the procedure.

Your doctor will ask you to lie on your left-hand side and bend your knees. First, they’ll put their finger into your anus to examine the area (they’ll wear gloves). They’ll then gently insert the colonoscope into your anus (back passage). Your doctor will use lubricating jelly to make this as easy as possible but it might still feel a bit uncomfortable.

Your doctor will pump air into your bowel through the colonoscope to inflate it slightly and give a better view of your bowel. You might pass wind when this happens but don’t worry – it happens a lot so your doctor won’t think anything of it. They’ll gently pass the colonoscope, which is flexible, through your bowel. They can rotate the tip 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. Your doctor might ask you to change your position during the procedure; for example, to turn from your side on to your back. This will help them to look at different areas of your bowel. They may press on your tummy to help move the colonoscope in the right direction.

Your doctor may take a small sample of cells (this is called a biopsy) or remove polyps (small growths on the lining of your bowel). Polyps are usually benign (not cancerous), but some can change into cancer over time. For more information, see our FAQ: Polyps. Your doctor can pass instruments through the colonoscope to remove polyps – this is usually quick and isn’t painful. The samples will be sent to a laboratory for testing to see if the cells are benign or malignant (cancerous).

What to expect afterwards

After your colonoscopy, you may feel a bit groggy and so you’ll need to rest until the effects of the sedative have passed. This will take an hour or so. 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 (ideally 12 hours) while the sedative wears off.

Your doctor may discuss some findings from the colonoscopy with you before you leave, or they may give you 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.

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 as 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.

You should be back to normal by the next day, and can go back to your normal diet. After 24 hours, you can drive again.

You won’t be able to fly for 24 hours after a colonoscopy. This is because of the air that your doctor pumps into your bowel during a colonoscopy. You’ll need to wait for your body to get rid of this before you fly. If your doctor removes a polyp or took a biopsy during your procedure, you’ll need to wait a couple of weeks because of the risk of bleeding. They won’t know in advance if a biopsy or polyp removal is necessary as it depends on what they find. So it’s best not to book a flight before you have the test.

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

  • continue to bleed from your back passage
  • have pain in your tummy that gets worse
  • feel weak, or develop a fever

Side-effects of a colonoscopy

As with every procedure, there are some risks associated with having a colonoscopy procedure. 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.

Side-effects 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. If you massage your tummy and walk around, it might help to relieve this. You may also bleed a little from your back passage if you’ve had a biopsy or a polyp removed.

Complications of a colonoscopy

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

  • Your doctor might not be able to see your entire bowel. This can happen for lots of reasons – for example, your bowel may not be empty or may be blocked. 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 happens.
  • The colonoscope and the other instruments your doctor uses during the procedure may damage or tear your bowel. This risk is higher if your doctor takes a biopsy or removes a polyp. But overall, it isn’t likely – it happens to about one person in every 1,200 who have a colonoscopy. If this does happen, you might need to have an operation to repair it.
  • You may have heavy bleeding if you have biopsies or polyps removed.

Frequently asked questions

  • Polyps are small, fleshy lumps that can develop in the lining of your bowel. They’re quite common and usually don’t cause any problems. But some types of polyp can grow into cancer over time. If your doctor finds any polyps during your colonoscopy, they’ll probably remove them or plan to remove them at a later date.

    About 35 in every 100 people develop a polyp in their lifetime, most often when they’re over 60. Men are slightly more likely to get them 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 don’t cause any problems. But there’s a small chance that over time a type of polyp called an adenoma will grow into a cancer. Most bowel cancers are thought to start as a polyp. So if your doctor finds any polyps during your colonoscopy, they’ll want to remove them.

    Once your polyp is removed it doesn’t usually come back. But you’re more likely to develop more polyps if you’ve had one, so you might need to have regular colonoscopies. How often you have these will depend on how many polyps you’ve had and when one was last found.

  • You should eat low-fibre foods for a couple of days before your colonoscopy, and just clear liquids the day before the procedure. This is to make sure your bowel is empty so that your doctor can see it clearly during the test.

    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 and fish, white bread, white pasta and rice, and cheese and eggs. You’ll also need to drink only clear fluids. This means fluids such as water, squash, clear soup, meat extract drinks, tea and coffee (without milk).

    The day before your colonoscopy, stop eating solid foods and have only clear fluids. Your hospital will send you full instructions before your colonoscopy appointment. It’s important to follow these carefully.

  • Bowel cancer screening aims to find cancer when it’s in the early stages – this is when treatment is more likely to work. Colonoscopy is one way to help diagnose bowel cancer.

    Bowel cancer screening is offered to everybody aged between 60 and 74 in England. The age range differs slightly in other parts of the UK. If you’re eligible for screening, you’ll be offered a test every two years.

    The bowel cancer screening kit contains a faecal occult blood (FOB) test that can detect small amounts of blood in your faeces (poo). The FOB test doesn't diagnose bowel cancer – the results show if you need to have your bowel examined. You’ll be sent a testing kit and instructions on how to take a sample of poo. You send this to a laboratory and should usually get the results back within two weeks.

    If blood is found in your poo during screening, you’ll be offered more tests to find out what’s causing this and one of these is a colonoscopy. Remember, you may have blood in your faeces because of conditions other than cancer. 

    As well as 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, looks at the lower part of your large bowel because that’s where most polyps are found. It only examines the last (lower) part of your large bowel.

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

  • Colonoscopes are reusable, but don’t worry – they’re thoroughly disinfected with detergents and chemicals before being used. This means that any bacteria, viruses and spores are killed and destroyed.

    Colonoscopes are cleaned in dedicated decontamination rooms and go through a strict process. First, they’re manually cleaned and then they’re cleaned in a machine called an endoscope washer-disinfector. Finally, they’re specially dried and stored safely for reuse. The process is monitored and carefully logged. This makes sure that colonoscopes are cleaned thoroughly without any chance of contamination. For example, used colonoscopes enter the decontamination room through one entrance and the clean (reprocessed) ones leave through another, so they never cross paths. 

    This is all done by trained professionals who are qualified to clean colonoscopes to the required standards.  

Did our information help you?

We’d love to hear what you think. Our short survey takes just a few minutes to complete and helps us to keep improving our health information.

About our health information

At Bupa we produce a wealth of free health information for you and your family. This is because we believe that trustworthy information is essential in helping you make better decisions about your health and wellbeing.

Our information is guided by the principles of The Information Standard and complies with the HONcode standard for trustworthy health information. We are also a proud member of the Patient Information Forum.

PIF member logo  This website is certified by Health On the Net Foundation. Click to verify.

Learn more about our editorial team and principles >

Related information

    • Colonoscopy. National Institute of Diabetes and Digestive and Kidney Diseases., published October 2014
    • Lower GI tract anatomy. Medscape., updated 17 November 2015
    • Colonoscopy | bowel cancer. Cancer Research UK., last reviewed 24 August 2015
    • Colorectal assessment. OSH colorectal surgery (online). Oxford Medicine Online., published October 2011
    • Colorectal cancer. BMJ Best Practice., last updated 10 March 2017
    • Colonoscopy. Medscape., updated 13 March 2013
    • Personal communication, Mr Stephen Pollard, Consultant Surgeon, Spire Leeds Hospital, 13 May 2017
    • Macrogols. NICE British National Formulary., reviewed April 2017
    • Laiyemo AO, Burnside C, Laiyemo MA, et al. Beverage intake preference and bowel preparation laxative taste preference for colonoscopy. World J Gastrointest Pharmacol Ther 2015; 6(3):84–88. doi:10.4292/wjgpt.v6.i3.84
    • Colon cancer. National Comprehensive Cancer Network., updated 6 June 2017
    • Colonoscopy. Beating Bowel Cancer., last reviewed 14 July 2015
    • Colonoscopy. American College of Gastroenterology., accessed 3 May 2017
    • Map of medicine. Colorectal cancer. International view. London: Map of medicine; 2015 (issue 4)
    • Flexible sigmoidoscopy. Medscape., updated 1 February 2016
    • X-ray (radiography) – lower GI tract. American College of Radiology., reviewed 1 March 2017
    • Bowel cancer. British Society of Gastroenterology., accessed 2 May 2017
    • Sonnenberg A. Sedation in colonoscopy. Gastroenterol Hepatol (NY) 2016; 12(5):327–29.
    • Rodríguez-García JL, Carmona-Sánchez R, Rosas-Vitorino C. Usefulness of oil lubrication during colonoscopy: a comparative study with the conventional technique. Rev Gastroenterol Mex 2016; 81(1):28–34. doi:10.1016/j.rgmx.2015.12.001
    • Polyps of the colon and rectum. American Society of Colon and Rectal Surgeons., accessed 2 May 2017
    • Assessing fitness to fly. Civil Aviation Authority., accessed 15 June 2017
    • Bowel screening. NICE Clinical Knowledge Summaries., last revised October 2014
    • Colorectal surgery. Oxford handbook of clinical surgery (online). Oxford Medicine Online., published March 2013
    • Colonic polyps. BMJ Best Practice., last updated 22 August 2016
    • Dietary fibre. British Nutrition Foundation., revised January 2017
    • Eating well. Living with bowel cancer. Beating Bowel Cancer., published May 2015
    • Bowel cancer screening: programme overview., last updated 13 November 2015
    • Screening for bowel cancer. Cancer Research UK., last reviewed 18 August 2015
    • Bowel scope screening. NHS Bowel Cancer Screening Programme., published 2 January 2013
    • BSG guidelines for decontamination of equipment for gastrointestinal endoscopy. BSG Working Party Report 2003. The Report of a Working Party of the British Society of Gastroenterology Endoscopy Committee
    • Health Technical Memorandum 01–06: Decontamination of flexible endoscopes Part B: Design and installation., published March 2016
    • Health Technical Memorandum 01–06: Decontamination of flexible endoscopes Part A: Policy and management., published March 2016
  • Reviewed by Rachael Mayfield-Blake, Freelance Health Editor, June 2017
    Expert reviewer, Mr Stephen Pollard, Consultant Surgeon
    Next review due June 2020