This page was reviewed under our medical and editorial policy by

Bradford Tan, MD, Chair, Department of Pathology and Laboratory Medicine, City of Hope Atlanta, Chicago and Phoenix

This page was reviewed on November 15, 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 U.S. Centers for Disease Control and Prevention.

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 colon 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.

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).

  • Low-fiber diet: Research has shown that limiting your diet for several days prior to having a colonoscopy achieves better results. You may be required to avoid fiber-rich foods (including certain fruits and vegetables, seeds, popcorn and whole grains), and instead consume only low-fiber, refined foods that are easily digested.
  • Clear liquid diet: Prep will likely start with a clear liquid diet (broth, lemon or lime gelatin, sports drinks, tea, apple or white grape juice, 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.
  • Adjust medications and supplements as directed: Some medications, including non-steroidal anti-inflammatory drugs (NSAIDs), can increase risk of bleeding or may interfere with the procedure, so make sure to let your doctor know which over-the-counter remedies, vitamins and supplements you’re taking.
  • Bowel cleansing protocol: 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.
  • Enema kit: Your doctor may also prescribe an enema, which is a liquid or gas that is flushed into your anus to clean out stool.

When you're consuming the colonoscopy prep diet, expect diarrhea and stay close to a bathroom. 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 a 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 may receive general anesthesia (asleep) or conscious sedation (awake, but not fully aware) during the colonoscopy. If polyps are discovered, your doctor may remove them at this time. If any abnormal tissue is found, a biopsy may also be taken.
  • Though you won’t feel pain during the procedure, you may experience bloating and cramping in your abdominal area for about an hour after your 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 kind of doctor performs a colonoscopy?

A gastroenterologist who has been specially trained in the procedure will perform your colonoscopy.

  • Guidelines outlined by the American Society for Gastrointestinal Endoscopy recommend that any doctor who performs a colonoscopy should have completed a gastroenterology fellowship or surgical residency program.
  • Additionally, according to the American College of Gastroenterology, the gastroenterologist should have a perforation rate of less than one in 500 colonoscopies—this is the rate at which the doctor has created a hole in the colon in error during the procedure.
  • Having a board-certified gastroenterologist perform the procedure is highly recommended, as they complete even more colonoscopy training and must take ongoing medical education classes.

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 recovery and side effects

Typically, patients are groggy after a colonoscopy because it takes time for the anesthesia to fully wear off. That means you'll need someone to drive you home. Plan to stay at the facility for one to two hours after your colonoscopy. During recovery, you may be offered something to drink and/or eat. It’s normal to feel bloated and gassy after the procedure; abdominal cramping may also occur. You’ll be encouraged to pass gas to help reduce bloating. You may pass liquid and/or liquid stool after your colonoscopy but, within one to five days, your bowel movements should return to normal. If you’ve had a biopsy, it’s normal to experience anal bleeding or bloody stool after the procedure. Delayed bleeding may also occur for up to two weeks afterward.

What can I eat after a colonoscopy?

Typically, patients may resume eating normally the next day unless the doctor advises otherwise. After the procedure, it’s recommended that you start with light meals, gradually introducing solid foods on the first day. It may be helpful to stick with bland, low-fiber foods for 24 hours after your colonoscopy.

For example, safe foods may include:

  • Milk and low-fat dairy
  • Cooked vegetables
  • Potatoes
  • Canned fruit and applesauce
  • Bananas, melons
  • Fruit and vegetable juices
  • Breads, cereals, pastas and crackers (not whole grain)
  • Pudding and gelatin
  • Eggs
  • Graham crackers
  • Broth
  • Weak tea

It may be helpful to avoid these foods the day of your procedure:

  • Foods high in fat
  • Hard and blue cheeses
  • Raw vegetables
  • Dried fruits
  • Whole grain breads, cereals, pastas and crackers
  • Spicy, fried or fermented foods
  • High-sugar foods
  • Nuts and seeds
  • Cured meats and fish
  • Alcohol and caffeine

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.

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