Tests and scans
A colonoscopy looks at the whole of the inside of the large bowel.
A doctor or specialist nurse, called an endoscopist uses a flexible tube called a colonoscope. The tube has a small light and camera at one end. The endoscopist puts the tube into your back passage (your anus and rectum) and passes it along the bowel. They can see pictures of the inside of your bowel on a TV monitor.
The test can take between 15 and 60 minutes. But you will be at the hospital for a few hours to allow time for waiting, preparation, and recovery.
You may need a colonoscopy:
to help find the cause of bowel symptoms
to look for early signs of bowel cancer as part of the national bowel cancer screening programme
to look for early signs of bowel cancer if you are at high risk of developing bowel cancer
as part of your follow up after treatment for bowel cancer
to look further into an abnormality found on another test such as a CT scan
You will have information from the endoscopy staff explaining what to do to prepare for your colonoscopy. It’s important that you read and follow the instructions. There is usually a number to call if you have any questions.
You need to have an empty bowel for the test. This is so the endoscopist can clearly see the inside of your bowel.
To empty your bowel you take medications (laxatives) the day before your test. You may hear this called bowel preparation or bowel prep.
After taking the laxatives you might need to use the toilet often and very suddenly, and you may have tummy cramps. It's best to stay at home for a few hours after taking laxatives so that you are near a toilet.
The endoscopy staff might ask you to eat a low fibre diet for 1 or 2 days before the test. It is very important to drink plenty of clear fluids. This includes:
water
black tea or coffee
strained clear soup
If you take iron tablets or other medicines that can make you you might need to stop these a week before the test.
Contact the endoscopy unit as soon as possible before your appointment if you take medicines to thin your blood or you are diabetic. You'll be given other instructions to follow.
You’ll receive clear instructions about what you can and can’t eat or drink before this test and on the day of the test.
You usually have a colonoscopy as an outpatient in the endoscopy department at the hospital.
Before the procedure you’ll see your endoscopist. They'll explain what will happen and ask you to sign a consent form. This is a good time to ask any questions you may have.
You wear a hospital gown and might also wear paper shorts with an opening at the back.
You're offered painkillers, and you might have medicine to relax you that can also make you drowsy. This is called sedation. You have these as injections into a small tube called a cannula in your vein in the back of your hand. Some hospitals use gas and air (Entonox). This is a fast acting pain relief that you breathe in through a mouth piece.
You lie on your left side with your knees drawn up towards your chest. The colonoscope goes into your back passage and passes into your bowel. The tube bends easily so it can pass around the curves in your bowel.
The endoscopist puts a small amount of gas into your bowel. This opens up the bowel to help them see all the bowel lining. This may feel uncomfortable, and you might have tummy cramps for a short time. You might also pass wind during the test, but this is normal.
The endoscopist may press on your tummy or ask you to change your position to help the tube pass through your bowel. During the test they take photographs of your bowel lining. They can also remove tissue samples (biopsies). If they see any growths ( ), they remove them with a wire loop put down the colonoscope.
Colonoscopies can be uncomfortable but shouldn't be painful.
Take a look at this short video about having a colonoscopy.
You go to a recovery area to rest if you have had sedation. A nurse looks after you until you are fully awake. You might be in the recovery area for a couple of hours. They offer you a snack and drink when you are ready.
You might have bloating and cramping pains after the test. This is due to the gas that goes into your bowel. It normally gets back to normal after a few hours.
If you have sedation you’ll need someone with you so they can take you home and stay with you overnight. Also for 24 hours after you shouldn’t drive, drink alcohol, operate heavy machinery or sign any legally binding documents.
Colonoscopy is a very safe procedure. But your nurse will tell you who to contact if you have any problems afterwards. Your doctors make sure the benefits of having a colonoscopy outweigh any possible risks.
Some of the possible risks include:
Tummy (abdominal) pain
You may have some cramping or pain in your tummy after the test. This is due to the gas put into the bowel. This should go away after a few hours. You may also experience some pain or tenderness if you had some tissue removed during the colonoscopy.
Bleeding
After having a biopsy or polyp removed, you might have some bleeding. This is usually a small amount and stops on its own within a couple of days. Contact the staff in the endoscopy unit or your hospital 24 hour advice line if the bleeding continues or is heavy.
Tear in your bowel
Very rarely there is a small tear in the bowel wall (perforation). If this happens it’s likely you would need surgery to repair the tear.
Difficulty breathing
There is a risk you might react to the sedation or pain relief drugs. It can cause a temporary feeling of difficulty with breathing. But this is rare. It is usually treated by giving you oxygen through a small plastic tube into your nose. Your nurse monitors you closely.
Allergic reaction
Rarely, people might have an allergic reaction to the sedation. This most often starts with weakness, sweating and difficulty breathing. Your endoscopist will ask if you have any allergies before your test. Tell them immediately if you feel unwell.
Before you go home, your doctor tells you if they've removed any polyps or taken any biopsies from your bowel.
The biopsy results can take up to 2 weeks. Your specialist writes to you with the results. If your GP referred you for the test, they should also receive a copy. Contact your doctor if you haven’t heard anything after a couple of weeks.
Waiting for test results can be a worrying time. You might have contact details for a specialist nurse. You can get in touch with them for information and support if you need to. It may help to talk to a close friend or relative about how you feel.
We have more information on tests, treatment and support if you have been diagnosed with cancer.
Last reviewed: 10 Jun 2025
Next review due: 10 Jun 2028
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