What is a colonoscopy?

A colonoscopy is a safe, effective way of finding out if you have a problem with the lower part of your digestive system.

During a colonoscopy, an endoscopist will look inside the lower part of your digestive system using a flexible tube around the size of an index finger. The tube will pass through your anus (back passage) and around the large bowel.

Sometimes during the procedure a small biopsy (piece of tissue) will be taken for further testing. You may feel a slight tugging sensation but this should not be painful.

Why am I having this procedure?

Your doctor or nurse has recommended this procedure to find out more about the cause of your symptoms. A colonoscopy can help to diagnose or investigate:

  • Bleeding from your anus
  • Pain in the lower abdomen (tummy)
  • Persistent diarrhoea
  • Changes to your bowel habits
  • A strong family history of bowel cancer
  • Being on a bowel cancer screening pathway
  • An existing condition that needs review e.g. crohn’s disease or colitis.

Will I have an anaesthetic?

Most people have sedation – this is different from a general anaesthetic as it does not ‘knock you out’. You will be drowsy and relaxed but able to respond, but it does have a slightly amnesic effect (loss of memory).

You will need to have a small needle inserted in the back of your hand to administer this. If you have sedation you must ensure you have a friend or relative to take you home and to stay with you for at least 24 hours after the procedure.

If you have not arranged for this in advance, we cannot give you sedation. Please also follow after care advice given to you at the time of the procedure.

Some patients choose not to have any anaesthetic or to have Entonox (the same as gas and air, often used during childbirth). If use Entonox, you can carry on with your day as normal after the procedure. You can discuss these options with your endoscopist on the day of your procedure.

How do I prepare for the procedure?

It is important that your bowel is empty for a clear view of the bowel lining and you will be given a laxative (a substance that speeds up bowel movement) to take before the test. You will receive instructions with your bowel preparation pack as follows:

  • Stop eating at 1pm on the day before your appointment.
  • Take the first dose (sachet A+B in 1 litre of water) of bowel preparation at 5pm and the second dose (sachet A+B in 1 litre of water) of bowel preparation at 9pm on the day before your procedure. Take an additional 500ml of clear fluid with each dose of bowel preparation.
  • You can take lots of clear fluids like lemonade, soft drinks (not blackcurrant) black tea, black coffee or clear soup.

If you suffer with any of the below problems, please ensure you contact the department before taking the laxative:

Gastrointestinal obstruction, perforation, ileus, gastric retention, acute intestinal or gastric ulceration, recent diverticulitis (within six weeks) Hypersensitivity to any of the ingredients listed on the laxative packaging
Toxic colitis or toxic megacolon Glucose-6-phosphate dehydrogenase deficiency
Severe acute inflammatory bowel disease Severe renal failure or cardiac failure
Dysphagia (unless via NG/J) Phenylketonuria
Reduced levels of consciousness Recently undergone gastrointestinal surgery 
Sulphur allergy Dialysis or renal transplant

In addition to the bowel preparation, you should eat a low fibre diet (reduce your vegetable intake) and no seeds or seeded bread three days before in preparation for your colonoscopy.

Fibre leaves a residue in your colon which, if you eat too much before your procedure, will obstruct the view of your colon and can also potentially block the scope. This can then mean the procedure needs to be repeated.

Foods that are okay Foods that are not okay
White bread or pasta Whole wheat bread or pasta
White rice or noodles Brown rice or noodles
Skinless cooked potatoes Raw or partially cooked vegetables
Skinless chicken or turkey Tough meat or meat with skin
Fish and other seafood Nuts, seeds, popcorn and fruits
Canned fruits without seeds or skin All salads
Eggs Beans and pulses
Rice Krispies, cornflakes, Ready-Brek or Special K Most cereals
Plain sponge cake, plain scone (no fruit) or cheese scone Jams or marmalade with skins or pips, peanut butter, chutney or pickles

If you are diabetic, please see the separate leaflet enclosed for further instructions on how to prepare for your colonoscopy.

If you have a stoma bag then you must bring a change of bag with you on the day of your procedure.

Do I need to stop any of my normal medications?

Certain medications need to be stopped prior to your procedure (please see the list below). Please also complete the medical questionnaire with a list of all your medications and bring them with you on the day of your procedure. 

Medication Advice
Iron tablets Stop seven days prior to the procedure
Anti-inflammatory tablets e.g. Nurofen, ibuprofen or Voltarol Stop five days prior to the procedure
Anti-coagulants e.g. warfarin, clopidogrel, aspirin, rivaroxaban, apixiban Follow the advice given to you at your out-patient appointment. If you have any questions please call 0208 375 1962.

Please continue any blood pressure, Parkinson’s and epilepsy medication as normal but don’t take diabetic medication on the day of the procedure unless instructed otherwise.

It is important to follow these instructions as otherwise your procedure may be cancelled on the day.

What will happen on the day of the procedure?

When you arrive please report to reception to check in. We aim to see you as close to your appointment time as possible and we will keep you informed if there are any delays.

You will be seen by a nurse prior to your procedure to discuss your medical history, perform some simple checks and explain what will happen. You will then be seen by an endoscopist who will discuss the risks and benefits of the procedure, review all the medications you are on and take your consent (permission) to go ahead.

Please ensure you ask the team any questions you may have at this point – no question is ever too silly or minor to ask so please feel free to ask the team caring for you if there is anything you want to know.

You will be asked to remove all your clothing and to change into a gown. Please do not wear any jewellery on the day of your appointment.

You will then have whichever type of anaesthetic you have chosen before the procedure begins (either sedation, Entonox or no anaesthetic). A nurse will be with you throughout the procedure which will take about 30 minutes to complete. You may experience periods of discomfort, particularly at the beginning of the procedure but it should not be painful.

You will be asked to lie down on your side with your knees bent. The endoscope will be inserted into your bowel through your anus. The endoscopist will pass some air down the tube to get a clearer view of the lining of your bowel – this may make you feel slightly bloated or to feel the urge to go to the toilet but you will not be able to as your bowel is empty.

Many people pass wind during the procedure, this is completely normal and nothing to be embarrassed about.

During the procedure the endoscopist may take biopsies (tissue samples), photographs or videos of your gut, even if it all looks normal. You will not feel this.

What happens after the procedure?

You will recover in the endoscopy department. If you have had sedation you will be transferred to the recovery area where nursing staff will monitor your condition for a few hours before you will need your friend or relative to take you home. You must not drink alcohol, operate machinery, drive or make important decisions for 24 hours after the procedure as the sedative can impair your judgement.

You must have someone to stay with you for 24 hours after receiving sedation otherwise your procedure may not be able to go ahead with sedation. Please note that if you have had sedation you cannot travel by either public transport or cab by yourself.

All patients will receive the results of their test on the day of the procedure, before leaving the department. If you had sedation, it is a good idea to have someone with you when this occurs because the sedation can make you forget what was discussed. If you had a biopsy taken it can take a few weeks to receive the result of the laboratory test.

Once we receive the result, you will be told the final diagnosis by the team who requested the procedure for you either in clinic or by letter. Copies of all reports will also be sent to your GP.

You will be discharged by a nurse who will give you the report of the procedure as well as discharge advice for you to follow.

What if I have problems after my test?

It is normal to feel bloated for a few days after your test however if you have severe pain, black tarry stools, a fever, are passing blood or have persistent bleeding you should go to your nearest A&E department for further advice.

Please also check the discharge sheet you were given when leaving the endoscopy department for any other specific advice to you.

What are the benefits, risks and alternatives to this procedure?

The benefits of a colonoscopy are that it is a very safe and effective test for diagnosing lower GI (gastro-intestinal) conditions.

A colonoscopy also means that, if needed, the endoscopist can take a biopsy (tissue sample) during the procedure which helps to aid a more accurate diagnosis.

Serious complications from this procedure are rare but it is important that you understand all the risks before you decide to go ahead:

  • There is a very small risk of damaging your colon during the test which can cause an infection, bleeding or perforation (tear) of the lining of your bowel.
  • Using sedation can cause breathing complications in 1 in every 200 procedures, which are not usually serious.

A colonoscopy is recommended as the most effective procedure for diagnosing your condition however alternatives include a barium enema (uses barium sulphate and X-rays to examine your bowel), CT scan, a sigmoidoscopy (similar to a colonoscopy but only investigates the lower part of your bowel) or faecal occult blood test (looks for hidden blood in your stool). However, in all of these procedures, biopsies cannot be taken you so may still need a colonoscopy.

Giving my consent (permission)

We want to ensure you feel involved and understand any decisions being made about your care and treatment. Therefore, if you decide to go ahead, you will be asked to sign a consent form. This states you agree to have the procedure and that you understand what it involves. You will be asked to to sign this on the day of your procedure.


Training doctors and other health professionals is essential to the continuation of the NHS and improving the quality of care. Your treatment can provide an important opportunity for such training under the careful supervision of an experienced doctor. You can, however, decline to be involved in the formal training of medical and other students – this won’t affect your care and treatment in any way.