During a colonoscopy, your doctor checks for abnormalities or disease in your large intestine, particularly the colon. They’ll use a colonoscope, a thin, flexible tube that has a light and camera attached.

The colon helps form the lowest portion of the gastrointestinal tract. It takes in food, absorbs nutrients, and disposes of waste.

The colon is attached to the anus via the rectum. The anus is the opening in your body where feces are expelled.

During a colonoscopy, your doctor may also take tissue samples for biopsy or remove abnormal tissue such as polyps.

A colonoscopy can be performed as a screening for colorectal cancer and other problems. The screening can help your doctor:

The American College of Surgeons estimates that 90 percent of polyps or tumors can be detected through colonoscopy screenings.

The American College of Physicians recommends a colonoscopy once every 10 years for people who meet all of the following criteria:

  • are 50 to 75 years old
  • are at average risk of colorectal cancer
  • have a life expectancy of at least 10 years

The British Medicine Journal (BMJ) recommends a one-time colonoscopy for people who meet all of these criteria:

  • are 50 to 79 years old
  • are at average risk of colorectal cancer
  • have at least a 3-percent chance of developing colorectal cancer in 15 years

If you’re at an increased risk for colorectal cancer, you may need more frequent procedures. According to the American Cancer Society (ACS), people who may need to be screened as often as every 1 to 5 years include:

Since a colonoscopy is a routine procedure, there are typically few lasting effects from this test. In the vast majority of cases, the benefits of detecting problems and beginning treatment far outweigh the risks of complications from a colonoscopy.

However, some rare complications include:

  • bleeding from a biopsy site if a biopsy was done
  • a negative reaction to the sedative being used
  • a tear in the rectal wall or colon

A procedure called the virtual colonoscopy uses CT scans or MRIs to take pictures of your colon. If you opt for it instead, you can avoid some of the complications associated with traditional colonoscopy.

However, it comes with its own disadvantages. For instance, it may not detect very small polyps. As a newer technology, it’s also less likely to be covered by health insurance.

Your doctor will give you instructions for a bowel preparation (bowel prep). You must have a clear liquid diet for 24 to 72 hours before your procedure.

The typical bowel prep diet includes:

  • broth or bouillon
  • gelatin
  • plain coffee or tea
  • pulp-free juice
  • sports drinks, such as Gatorade

Make sure not to drink any liquids containing red or purple dye because they can discolor your colon.


Tell your doctor about any medications you’re taking, including over-the-counter drugs or supplements. If they can affect your colonoscopy, your doctor may tell you to stop taking them. These might include:

Your doctor may give you a laxative to take the night before your appointment. They’ll likely advise you to use an enema to flush out your colon the day of the procedure.

You may want to arrange for a ride home after your appointment. The sedative you’ll be given for the procedure makes it unsafe for you to drive yourself.

Just before your colonoscopy, you’ll change into a hospital gown. Most people get a sedative and pain medication through an intravenous line.

During the procedure, you’ll lie on your side on a padded examination table. Your doctor may position you with your knees close to your chest to get a better angle to your colon.

While you’re on your side and sedated, your doctor will guide the colonoscope slowly and gently into your anus through the rectum and into the colon. A camera on the end of the colonoscope transmits images to a monitor that your doctor will be watching.

Once the colonoscope is positioned, your doctor will inflate your colon using carbon dioxide. This gives them a better view.

Your doctor may remove polyps or a tissue sample for biopsy during this procedure. You’ll be awake during your colonoscopy, so your doctor will be able to tell you what’s happening.

The entire procedure takes 15 minutes to an hour.

After the procedure is done, you’ll wait for about an hour to allow the sedative to wear off. You’ll be advised not to drive for the next 24 hours, until its full effects fade.

If your doctor removes tissue or a polyp during a biopsy, they’ll send it to a laboratory for testing. Your doctor will tell you the results when they’re ready, which is normally within a few days.

You’ll likely have some gas and bloating from the gas your doctor placed into your colon. Give this time to get out of your system. If it continues for days after, it could mean there’s a problem and you should contact your doctor.

Also, a little bit of blood in your stool after the procedure is normal. However, call your doctor if you: