A colonoscopy is a procedure that enables viewing of the entire length of the large intestine. Among other situations, a health professional prescribes this exam in the following cases:


A colonoscopy lasts 15 to 30 minutes. During this procedure, the doctor inserts a thin, flexible tube, about as thick as a finger, in your rectum. This tube, called a “colonoscope”, has a miniature camera at the end of it, which enables the doctor to see inside the large intestine and transmit images on a screen.

As the interior of the intestine is easier to see when it is inflated, the doctor pumps air into it using a machine. This can cause distension that can be uncomfortable or painful, the doctor may give you medication (analgesic) to reduce the discomfort or pain. They may also give you a medication (sedative) to help you relax during the procedure.

In addition to examining the large intestine, the doctor may sometimes perform other procedures at the same time, including:

  • The removal of polyps
  • A biopsy

Removing polyps

A colonoscopy sometimes reveals polyps in the intestine. Polyps are small masses of flesh that look like warts. They grow on the inner lining of the large intestine. Because some polyps can develop into colorectal cancer, doctors generally prefer to remove them as a preventive measure.


If deemed necessary, the doctor will perform a biopsy. A biopsy involves removing a piece of tissue on the lining of the large intestine.

The removal of polyps and biopsies are procedures that are not painful. The polyps and tissues collected are then analysed in a laboratory to see if they’re cancerous or if there is another disease. The results of the analysis will be sent to a doctor, who will then conduct the appropriate follow up with you.


The day before your colonoscopy, you must follow a special diet and take a laxative to clear all the stool from your intestine. It is important that you take all the preparation (laxative) and follow the diet recommendations in order to make sure that your intestine is completely empty for the doctor to examine the interior.

If the doctor cannot see the interior of your intestine clearly, you must reschedule, restart the preparation and redo the exam.

Ask someone ahead of time to take you on your errands. You must not drive for 24 hours following the exam. This is the time needed for the sedatives to be completely eliminated from your system. For the same reason as well, it is preferable that you wait a few days before making important decisions.

Possible complications

Although rare, complications can occur before, during or after the examination.

Before the examination

  • An intolerance to the prescribed laxative may cause headaches and vomiting

During the examination

  • The sedative may cause certain reactions. For instance, a sudden onset of redness or pimples on the skin, a drop in blood pressure, as well as cardiovascular or respiratory discomfort
  • Heavy bleeding may occur when the doctor removes polyps or performs a biopsy (1 in 100 cases)
  • The removal of polyps may result in perforation of the intestine (2 in 1,000 cases). An antibiotic treatment or an operation may be necessary
  • Death may result in extremely rare cases

After the examination

  • An infection characterised by fever or chills may occur within 24 hours after the exam

If you experience complications after your colonoscopy, you may refer to the instructions given to you by the doctor or the nurse after your exam.

Last update: September 29, 2023


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