Approved by the Cancer.Net Editorial Board, 11/2016

A colonoscopy is a way to view the entire large intestine. The large intestine helps the body process waste. The first 5 to 6 feet of the large intestine is the colon. The last 6 inches of the large intestine is the rectum, ending at the anus.

How a colonoscopy works

A colonoscopy uses a device called a colonoscope. A colonoscope is a thin, flexible tube with a light and camera at the end. Before a colonoscopy, the doctor gives you pain medication and a sedative to reduce discomfort. During the colonoscopy, the doctor inserts a colonoscope into the anus and through the colon. The colonoscope captures an image on a video monitor for the doctor to see. It also allows the doctor to remove a small amount of tissue for examination later. This is called a biopsy.

Doctors use a colonoscopy to find the cause of colorectal problems. It is also used to screen for colorectal cancer in people who have no symptoms.

Who does my colonoscopy?

Typically, a gastroenterologist performs a colonoscopy with the help of a nurse. It is usually done in a doctor's office or at a hospital. A gastroenterologist is a medical doctor who focuses on the function and diseases of the gastrointestinal system. The gastrointestinal, or GI, system includes the esophagus, stomach, small intestine, large intestine, pancreas, gallbladder, bile ducts, and liver. A surgeon may also perform a colonoscopy.

Getting ready for a colonoscopy

When you schedule the exam, your doctor will give you detailed instructions on how to prepare.

  • Tell your doctor about medications you are taking. Be sure to ask whether you should take them on the day of the test. Discuss any drug allergies or medical conditions you have.

  • Your colon must be empty during the colonoscopy. You will need to avoid solid food and drink only clear liquids for one to three days before the procedure. A liquid diet may include foods such as fat-free bouillon or broth, black coffee, strained fruit juice, or gelatin.

  • You will also need to take a laxative or give yourself an enema the day or night before the colonoscopy to empty your colon. If your doctor prescribes a laxative, it will be either a pill or a powder that you mix with water before drinking.

  • After the procedure, you will be groggy from the sedative. Ahead of time, arrange for a friend or family member to drive you home.

  • Check your insurance coverage to see if it includes the medical facility where you will receive the test, the doctor who will perform the colonoscopy, and the anesthesiologist, who will give the sedation.

  • You will be asked to sign a consent form stating you understand the risks and benefits of the colonoscopy and agree to have the test.

  • Talk with your doctor about any concerns you have about the colonoscopy.

During the procedure

  • When you arrive for your colonoscopy, you will remove your clothing and change into a hospital gown.

  • You will then lie on your side on an examining table in a private room with a sheet draped over your body.

  • The nurse will give you pain medication and a sedative through an intravenous (IV) line. This is inserted in a vein in your arm. You may feel a slight sting where he or she inserts the needle.

  • The doctor will insert the colonoscope and blow air into your colon. This will inflate it so the doctor can better see the colorectal lining. As the doctor guides the colonoscope through the curves of your colon, you may need to change your position slightly to allow better access.

  • If there is an abnormal growth, or polyp, in your colon, the doctor will use a tool at the end of the colonoscope to remove it or perform a biopsy. This usually does not cause pain. But bleeding may occur at the site where the tissue is removed. The doctor can stop the bleeding using the colonoscope.

The procedure typically takes about 30 to 60 minutes to complete.

Generally, the pain medicine and sedative you receive before the colonoscopy should limit the discomfort you may feel. You may also feel discomfort from lying still for an extended time. If you feel cramping, taking slow, deep breaths may ease this pain.

Rarely, the colonoscope may puncture the colon wall, and surgery may be required to repair the hole. Talk with your doctor if you have concerns about this small risk.

After the procedure

You will stay at the facility where you had the procedure for up to 2 hours. You must wait for the effects of the sedative to wear off. If you received anesthesia or a sedative, you should not drive a vehicle, operate machinery, or make critical decisions for the rest of the day. A friend or family member can drive you home.

You can expect to resume your normal activities the day after your colonoscopy. Contact your doctor immediately if you have:

  • Severe abdominal pain

  • A fever

  • Bloody bowel movements

  • Dizziness

  • Weakness 

Questions to ask your doctor

Before your colonoscopy, consider asking your doctor these questions:

  • Why do you recommend that I have a colonoscopy?

  • What will happen if I don't have this exam?

  • Who will perform the colonoscopy?

  • What will happen during the test?

  • How long will the procedure take?

  • Will it be painful?

  • Will I receive medications to reduce discomfort?

  • What are the risks and benefits of having a colonoscopy?

  • Can I take my regular medications the day of the test? Which ones should I not take and when can I take them again?

  • Whom can I talk to about the out-of-pocket costs of this test?

  • Will I need to avoid any activities after the colonoscopy?

  • When will I learn the test results?

  • Who will explain the results to me?

  • Will I need additional tests?

More Information

Tests and Procedures

Types of Endoscopy

Cancer Screening

Additional Resources

American College of Gastroenterology: Colonoscopy

National Institute of Diabetes and Digestive and Kidney Diseases: Colonoscopy