The information on this page was reviewed and approved by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on September 21, 2021.


A colonoscopy is considered the gold standard for detecting colon and rectal cancers early—sometimes even before they become cancers. As many as nine out of every 10 people whose colorectal cancers are found early and treated appropriately are still alive five years later, according to the CDC.

Why do I need a screening colonoscopy?

The American Cancer Society recommends that people who are at average risk for colorectal cancer start regular screening at age 45, with a colonoscopy exam (or stool test). Other organizations suggest starting such screening at age 50 if you are at average risk.

Average risk for colorectal cancer means that you don’t have a:

  • Personal or family history of colorectal cancer or certain types of precancerous polyps
  • Personal history of inflammatory bowel disease
  • Genetic syndrome that predisposes you to colon cancer
  • History of radiation to the abdomen or pelvic area to treat a prior cancer

If you’re at an increased risk for colon cancer, you may need to start screening earlier and take other precautions. Other reasons your doctor may suggest a colonoscopy include unexplained changes in bathroom habits, abdominal pain or unexplained weight loss. In these instances, the colonoscopy is considered ‘diagnostic’ and isn’t a screening tool.

Learn more about colorectal cancer screening guidelines

How do I prepare for a colonoscopy?

Prepping requires a thorough cleansing of the colon so little or no stool remains. If there is stool, your doctor can’t see the lining of your colon, and you may need to repeat the test (and the prep).

  • Prep will likely start with sticking to a clear liquid diet (broth, lemon or lime gelatin or sports drinks, tea, apple or white grape juice and water) for one to three days before the procedure. It’s important to avoid red- and purple-colored drinks or gelatin, as these can look like blood during your colonoscopy.
  • Some medications, including NSAIDs, can increase risk of bleeding or may interfere with the procedure, so make sure to let your doctor know what over-the-counter remedies, vitamins and supplements you’re taking beforehand.
  • You’ll also need to take a combination of laxatives, most often on the night before and the morning of the procedure. They can be mixed with clear liquid and/or taken as pills, and they work by loosening stool and increasing bowel movements.
  • Your doctor may also prescribe an enema, a liquid or gas that is flushed into your anus to clean out stool.

Expect diarrhea and stay close to a bathroom during prep days. How can you tell if you prepped correctly? You should be passing liquid that is clear enough to see through. Make sure to drink enough fluids during bowel prep to avoid dehydration.

What can I expect during the colonoscopy?

A colonoscopy typically takes about 30 to 60 minutes, depending on if the doctor needs to remove any polyps or take biopsies. Patients should expect to be at the facility for up to three hours to ensure adequate prep and recovery.

  • During the procedure, the doctor inserts a colonoscope (a thin, flexible, lighted tube with a lens and a scraper tool for removing tissue) through the anus into the rectum and colon.
  • Air is pumped into the colon to expand its circumference and allow for a better view of its lining. You’ll be lying face down on a table during the procedure.
  • You may receive general anesthesia (asleep) or conscious sedation (awake, but not fully aware) during the colonoscopy.

Your doctor will discuss anesthesia options in advance of the procedure. These medicines are usually given intravenously, along with pain medication. A doctor, nurse or another member of the health care team will check your vital signs and make sure you are as comfortable as possible during the entire procedure.

If your doctor sees any abnormal or possibly precancerous or cancerous growths, they typically remove them during the colonoscopy. These precancerous polyps can grow for years and change into cancer without causing any symptoms.

What happens after the colonoscopy procedure?

Your doctor will let you know how it went and whether any polyps were found or removed and sent off to a lab for a biopsy. It may take a few days to get these results, which will guide the next steps.

Typically, patients are groggy after a colonoscopy. This is because it takes time for the anesthesia to fully wear off, and you'll need someone to drive you home. During recovery, you may be offered something to drink and/or eat. It’s normal to feel bloated and gassy after the procedure. You’ll also be encouraged to pass gas to remove any of the bloating. Typically, patients can resume eating normally the next day unless the doctor advises otherwise.

Colonoscopy complications and risks

A colonoscopy is considered a safe and life-saving procedure, but like with all medical procedures, it’s not without risks. Some of the most common risks include:

  • Bleeding, especially if polyps are removed or a biopsy is performed
  • Delayed bleeding up to two weeks after the colonoscopy
  • A reaction to the anesthesia

Another risk—and one that is feared—is a perforation or hole through the wall of the colon. It's important to know the risk of a perforated colon is extremely low. The care team will review all possible risks with you before the procedure.