Colonoscopy: What to Know

Medically Reviewed by Minesh Khatri, MD on August 31, 2022
Written by WebMD Editorial Contributors
3 min read

If your doctor recommends you have a colonoscopy, don’t worry. You may think it’s going to be a terrible procedure, but it won’t be. Most likely you won’t even be awake to remember it. (Most people consider the preparation for the procedure to be the worst part.)

A colonoscopy is an exam your doctor uses to look inside your large intestine for possible causes of things like abdominal pain, rectal bleeding, or changes in bowel habits.

Colonoscopies are also used to prevent colorectal cancer, and it is recommended that you start having them at age 45. During a colonoscopy abnormal growths, called polyps, can be removed before they transform into cancers.

Before giving you a colonoscopy, your doctor will want to know about any special medical conditions you might have, including:

Also tell your doctor if you have diabetes or take drugs that could affect blood clotting. They may need to adjust to these medications before the procedure.

To have a successful colonoscopy, you must have a clean colon. That means you need to restrict your diet at least 24 hours before the procedure. Solid foods usually are off-limits, but your doctor will usually say it’s OK to have clear liquids, such as:

  • Coffee
  • Broth
  • Water
  • Sports drinks

The next step is to empty your bowel. Your doctor probably will ask you take care of this in one of a couple ways:

  • Drink a prescribed laxative -- commonly polyethylene glycol -- that makes you have to go
  • Supplement the laxative with a series of enemas

They might tell you to do it the night before your colonoscopy, or the night before and the morning of the procedure. Be sure to follow their directions exactly.

Make sure you arrange to have someone take you home after the colonoscopy. You will be sedated, meaning you won’t be awake for the procedure. It won’t be safe for you to drive or operate machinery for at least 8 hours afterward.

During your colonoscopy, you’ll lie on your left side on an exam table. You’ll get sedatives through an IV in your arm, and you’ll go to sleep.

During the procedure, the doctor puts a tube-like instrument called a colonoscope into your rectum. It’s long but only about a half-inch across. It has a light and video camera on the tip so the doctor can see the lining of your colon and tell if there is any problem.

The colonoscope also includes a tube that lets your doctor pump in air and inflate your colon. This will give them a better view of your colon and its lining.

During the exam, your doctor can use a small snare in the colonoscope to take tiny samples of your colon for testing, which is called a biopsy. They can also use it to take out abnormal growths called polyps.

The entire procedure should take between 20 and 30 minutes. You’ll stay in a recovery room for about 30 minutes to an hour to wake up from the sedative.

You may have cramping or pass gas, but these are normal. You can eat regularly after you leave the doctor’s office.

Make sure you understand the instructions you get before you go home. You may need to avoid certain medicines, such as blood thinners, for a day or two if your doctor did a biopsy or removed any polyps.

Bleeding and puncture of the colon are rare but possible problems in a colonoscopy. Call your doctor right away if you have any of the following:

  • More than a little bleeding, or bleeding that lasts a long time
  • Severe abdominal pain, fever, or chills