A colonoscopy is the most effective way to diagnose bowel cancer. A thin, flexible tube called a colonoscope is used to examine the lining of the bowel for abnormalities.

The bowel needs to be completely empty before the test. Your doctor or nurse will tell you what you can eat and drink the day before the test, and you will also take a laxative.

Before the colonoscopy, you may be given a sedative to help you relax. Once you are lying on your side, a thin, very flexible tube with a camera on the end (colonoscope) is passed gently into your back passage. The doctor or nurse will look inside your bowel. They use the camera to take photographs and they may also take samples of cells to be examined later.

Having a colonoscopy can be uncomfortable but is usually not painful. If you are in pain during the test, you can have painkillers.

It can take up to 3 weeks before the results of your colonoscopy are ready. This can be an anxious time. Try talking to someone about how you are feeling.

What is a colonoscopy?

Having a colonoscopy

Dr Ana Wilson, Consultant Gastroenterologist, explains what to expect if you're having a colonoscopy.

About our cancer information videos

Having a colonoscopy

Dr Ana Wilson, Consultant Gastroenterologist, explains what to expect if you're having a colonoscopy.

About our cancer information videos

Colonoscopy assessment

You will usually be assessed at your local hospital or screening centre. In some parts of Scotland and Wales, you may be assessed over the phone.

The nurse will explain what your test result means and answer your questions. They will also assess whether you are fit enough to have a colonoscopy. They will explain how a colonoscopy is done, as well as the benefits and risks of having it. The nurse may be called a specialist screening practitioner (SSP).

Some people may not be able to have a colonoscopy. This may be because of other health conditions or medications they are taking. If a colonoscopy is not suitable in your situation, you may be offered a different test. This is usually a virtual colonoscopy (sometimes called a CTC scan or colonogram).

Before a colonoscopy

Your bowel has to be completely empty before you have a colonoscopy. Your doctor or nurse will tell you what you can eat and drink the day before the test. You will also take a medicine to empty your bowel. This is called a laxative. Just before the test, you may have a sedative as an injection into a vein (intravenously). This will help you feel more relaxed and sleepy while you have the colonoscopy.

The colonoscopy is usually done in the hospital endoscopy unit. It takes about 30 minutes. The test can also see if there are any polyps in the bowel.

‘The test only takes a day’s prep to make sure your bowel is empty. You can ask to be sedated so you don’t feel a thing. And for your own peace of mind you can walk away knowing, instead of guessing, what may be in there.’ Sharon


Having a colonoscopy

Once you are lying comfortably on your side, the doctor or nurse will gently pass a flexible tube into the back passage (rectum). This tube is called a colonoscope. There is a tiny light and camera on the end of it. During the test, the doctor or nurse will use this to photograph any areas of the bowel that look abnormal. They may also take samples (biopsies) from these areas. They will send the biopsies to the laboratory to see if there are any cancer cells.

A colonoscopy
A colonoscopy

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Having a colonoscopy can be uncomfortable. If you do have pain, it is usually mild. If you find it very painful, tell the doctor or nurse straight away. They may give you Entonox®, which is a gas that can relieve pain. It is sometimes called gas and air. You breathe it in through a mouthpiece.

I had sedation and felt no pain. I did not feel the biopsies. I bled a bit afterwards, but I was fine. Not my favourite thing, but quite doable!


After a colonoscopy

Most people are ready to go home a couple of hours after their test.

If you had a sedative, you will need someone to collect you from the hospital. After having a sedative, you should have someone with you for 12 hours. You should not drive for 24 hours.

If you only had Entonox® (gas and air), you should be able to drive home when the nurses say you have recovered. You will not need someone to stay with you overnight.

It is rare to have any serious problems after the test. Contact your GP or go to your nearest emergency department (A&E) straight away if you:

  • have severe tummy pain
  • have a high temperature
  • are being sick
  • are bleeding from the back passage.

Sometimes it is not possible to see the whole bowel during a colonoscopy. This can happen if the bowel is not completely empty. It may also happen if the colonoscope cannot pass around a bend in the bowel to reach the end. If this happens, you may be asked to have another colonoscopy, or a virtual colonoscopy.

Risks of colonoscopy

Most people who have a colonoscopy have no problems. But rarely, there can be problems.

A small number of people have heavy bleeding after having a polyp removed or a biopsy. This can usually be treated quickly during the test. But some people may need to be admitted to hospital to have this treated.

Rarely, the bowel can be torn or damaged. If this happens, you will usually need an operation to repair the tear.

Very rarely, a person may die as a result of having a colonoscopy. This happens in about 1 in every 10,000 colonoscopies. You will be assessed before you have a colonoscopy to check it is suitable for you. If the assessment shows you may be at a higher risk of problems, you will be offered a different test.

Colonoscopy results

You should get a letter with the results of your colonoscopy within 3 weeks. Some hospitals may phone you with the results. If you have polyps removed or biopsies taken during your test, the letter will say if you need further tests or a follow-up appointment. Your GP will also get a letter with your results.

Waiting can be an anxious time. You may find it helps to talk to a relative or close friend. Or you can talk to one of our cancer support specialists on 0808 808 00 00.

Normal result

This means no polyps or cancer have been found in your bowel. Or some people may have small polyps that do not need to be removed. Even if you have a normal result, it is important to be aware of bowel cancer symptoms in future.

After 2 years, you will be invited to take part in bowel cancer screening with a home testing kit again. You will only be invited if you are still within the screening age range for your country.


Some people may have polyps that need to be removed. This might be because there are:

  • quite a lot of polyps
  • one or two large polyps.

Polyps can usually be removed during the colonoscopy. This can help prevent bowel cancer developing.

The removed polyps will be sent to a laboratory to be checked by a doctor who specialises in looking at cell and tissue samples (pathologist). Depending on the results, you may be invited to keep having bowel cancer screening every 2 years. Or you may have another colonoscopy in the next few years.

Polyps may come back after being removed.

Other non-cancerous bowel conditions

Some people may have other changes in their bowel. The most common findings are piles (haemorrhoids) or a bowel condition such as diverticular disease. These conditions may not need treatment if they are not causing symptoms.

If this test shows you have a bowel condition, you can ask your GP for information and advice.


Around 1 in 10 people who have a colonoscopy after an abnormal FOB or FIT test result (about 10%) are diagnosed with bowel cancer. If a cancer is found, you will be referred to a cancer specialist for treatment.

There is a good chance of curing cancer if it is found at its earliest stage. Around 9 out of 10 bowel cancers (about 90%) can be cured if found at an early stage.

If you are diagnosed with cancer in the colon or rectum, you may find it helpful to read our information about colon cancer or rectal cancer.

Back to Bowel screening

The FOB and FIT tests

These tests check for tiny amounts of blood in poo, which can be a sign of polyps or bowel cancer.

Bowel scope screening

This test looks at the lower part of your large bowel. It can help find cancer at an early stage.

Virtual colonoscopy

This test is also called a CT colonography. It uses a CT scanner to build a picture of the bowel.

Be bowel aware

It is good to be aware of the symptoms of bowel cancer and ways to reduce your risk.