• This is a procedure to inspect the large bowel, or colon (marked in yellow on the diagram). The procedure involves passing a thin tube into the bottom. Because this can be uncomfortable, the procedure is usually done under sedation. It is a low risk procedure but care has to be taken with the amount of sedation given.

Before the procedure

In order for your doctor to get the best possible view and make the colonoscopy easier, your large bowel needs to be cleaned out. How this is done is explained on a separate page, detailing the preparation for colonoscopy. You need to have nothing to eat or drink for 4 hours before the procedure is done, however you make take medications with a sip of water.

Special considerations

Some medications may need to be stopped for up to a week before the procedure. These might include iron tablets, aspirin, clopidogrel, anti-inflammatory drugs. If you have significant heart disease, such as previous heart attacks or coronary stents, you will probably need to continue on your aspirin and/or clopidogrel, so please make sure you discuss this with your doctor.
If you have diabetes, valvular heart disease, a permanent pacemaker or are taking blood thinning medications such as warfarin, dabigatran or rivaroxaban it is important to discuss this with your doctor before you colonoscopy is organised as special arrangements may be necessary.


During the procedure

Before the procedure starts, intravenous sedation is given. If there is an area of abnormality seen, a biopsy may be taken. A polyp is a small growth attached to the bowel wall which over time can occasionally become a cancer. If polyps are found they are usually removed at the time of the examination. Most polyps can be burnt off by placing a wire snare around the base and applying an electric current. Removal of polyps carries a risk of bleeding and perforation.

After the procedure

When you wake up you may feel a little bloated. This is due to the gas that was inserted during the procedure. This will pass over the next hour or so. Very rarely, you may pass a small amount of blood.
You will remain in the hospital recovery area for 1-2 hours until the effects of the medication wear off. The results of the colonoscopy will be discussed with you during this time and a letter will be sent to your local doctor. Usually biopsy results are available after 3-5 days.
Because of the sedation given, it is very important that you do not drive a car, travel on public transport alone, operate machinery, sign legal documents or drink alcohol on the same day as the test. You should have a friend or relative take you home after the procedure and stay with you overnight.

Safety and risks

Serious complications of colonoscopy are rare, occurring less than one in every thousand examinations. However complications can occur and include the following.

  • Intolerance of the bowel preparation: Some people develop dizziness, headaches, vomiting, dehydration & electrolyte imbalances.
  • Perforation (a hole or tear in the bowel wall): This is a very serious complication and often requires surgery to fix the problem. The surgery might involve a forming a colostomy (stoma).
  • Major bleeding from the bowel: This is more likely to occur if polyps are removed and occasionally at the time of a biopsy. Rarely, the colonoscopy itself can tear major blood vessels. It is possible if these serious complications occur that you may require a blood transfusion or surgery.
  • Sedation related: Whenever intra-venous sedation is given there is a risk of allergic reaction to the drugs or aspiration (pneumonia from inhaling gastric contents while sedated).  Low blood pressure and low oxygen levels can occur but you will be closely monitored during the procedure and this can usually be rapidly corrected.
  • No procedure is perfect: Although colonoscopy is considered the most accurate way to examine the bowel, lesions (eg. polyps and cancers) can be missed. This is more likely to occur if the bowel clean out is not ideal.
  • Rare side effects can occur with any procedure. Death is a very remote possibility.

The colonoscope is completely cleaned between each patient to avoid the risk of transmission of serious infections such as HIV, hepatitis B or C.