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Your surgeon has determined that you need a colonoscopy for further evaluation or treatment of your condition. This information sheet should help you understand the procedure. It includes answers to the questions that people most frequently ask.

Please read the information sheet carefully. If you have any other questions, please feel free to discuss them with the endoscopy nurse or your surgeon before the examination begins.

A colonoscopy is a procedure that lets your surgeon check the lining of your colon (large bowel) for abnormalities. This is done by inserting an endoscope through your rectum and advancing it slowly around your large bowel. An endoscope is a thin flexible tube that allows the surgeon to see inside your bowel.

A flexible sigmoidoscopy is similar to a colonoscopy, but it only examines the lower part of the colon, while a colonoscopy examines the whole large bowel.


Your colon must be completely clean for the procedure to be accurate and complete. Your appointment letter includes instructions about where to pick up the bowel preparation you need to take beforehand. You should pick up the bowel preparation at least one week before your procedure.

Please follow the instructions carefully. You may experience diarrhoea overnight before the examination, but this is normal.


You can take most medications as usual, but some can interfere with your preparation or the examination.

During the colonoscopy

You'll normally be given a sedative for pain relief and to relax you, so you may have little or no memory of the examination. Without the sedative you could experience abdominal discomfort. A few people request little or no medication. If that's what you want, please let us know at the time of the examination.

There's often a feeling of pressure, bloating or cramping at times during the procedure. The examination itself will usually be over within 30 minutes, although sometimes it takes longer.

90% of people can have the whole of their large bowel examined, so the aim of the examination is achieved for most people.

If your surgeon thinks an area of your bowel needs to be evaluated in greater detail, an instrument will be passed through the colonoscope to obtain a biopsy (a sample of the colon lining). This is painless.

This specimen is sent to the Pathology Laboratory for analysis. Sometimes polyps or small mushroom-like growths are found which can be removed. This minor procedure, called a polypectomy, avoids an open abdominal examination. If polyps are found, they're removed because some can become cancerous.

Possible complications

Colonoscopy and polypectomy are generally safe when performed by surgeons who've been specially trained and are experienced in endoscopic procedures.

After the colonoscopy


You need to arrange for someone to pick you up from the Day Surgery Unit (Lower Ground Floor, Te Nikau, Grey Hospital & Health Centre) approximately two hours after the examination.

You shouldn't be alone for the next 24 hours. Even if you feel alert after the procedure, your judgement and reflexes may be impaired by the sedation. Don't drive a vehicle, operate any machinery, drink alcohol, ride on public transport alone, sign any legal documents, or make any important decisions for 24 hours.

You may have some abdominal cramping or bloating because of the air introduced into your colon during the examination. This should disappear quickly with the passage of gas. Generally, you should be able to eat and drink after your colonoscopy.

Further information

You've been given this information to prepare you for the procedure. If you have questions about your need for a colonoscopy or about other tests, don't hesitate to speak with your doctor. If you have any questions that haven't been answered, please discuss them with the endoscopy nurse or surgeon before the examination begins. If you need any further explanation, please phone one of the following numbers:

For after-hours enquiries, phone the General Ward, Te Nikau, Grey Hospital & Health Centre on (03) 769-7400 ext. 5707.

Written by HealthInfo clinical advisers. Last reviewed June 2017. Last updated November 2019.

See also:

Colonoscopy & sigmoidoscopy if you have diabetes

Having an anaesthetic

Page reference: 75778

Review key: HICOL-20309