Approved by the Cancer.Net Editorial Board, 07/2018

Listen to the Cancer.Net Podcast: Colonoscopy – What to Expect, adapted from this content.

A colonoscopy is a way to view the entire large intestine. It can help find the cause of problems in a part of the large intestine called the colon. It is also used to screen for colorectal cancer.

About the large intestine and colon

The large intestine helps the body process waste. The first 5 to 6 feet of the large intestine is called the colon. The last 6 inches of the large intestine is the rectum, ending at the anus.

The drawing below shows the different parts of the colon and rectum.

This illustration shows the 5 sections of the colon and rectum. The ascending colon is the beginning the large intestine into which the small intestine empties; it begins on the lower right side of the abdomen and then leads up to the transverse colon. The transverse colon crosses the top of the abdomen from right to left, leading to the descending colon, which takes waste down the left side. Finally, the sigmoid colon at the bottom takes waste a few more inches, down to the rectum. A cross-section of the rectum and sigmoid colon shows where waste leaves the body, through the anus. Copyright 2004 American Society of Clinical Oncology. Robert Morreale/Visual Explanations, LLC.

How a colonoscopy works

A colonoscopy uses a device called a colonoscope. This thin, flexible tube has 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.

Who does my colonoscopy?

Typically, a gastroenterologist performs a colonoscopy with the help of a nurse. 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

A colonoscopy is usually done in a doctor's office or at a hospital. When you schedule the exam, your doctor will give you detailed instructions on how to prepare. Here are some things to keep in mind:

  • 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. Make sure to tell your doctor if you are taking a blood thinner or aspirin. These medicines often need to be stopped several days before the procedure.

  • Your colon must be empty during the colonoscopy. You will need to avoid solid food and drink only clear liquids for 1 to 3 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.

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

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

  • 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 health care team about any concerns you have about the colonoscopy.

During the procedure

You should expect the procedure to take about 30 to 60 minutes to complete. 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 to limit the discomfort you may feel. 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 then insert the colonoscope and blow air into your colon. This will inflate your colon so the doctor can better see the lining of the colon and rectum. 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.

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

During the procedure, you may feel discomfort from lying still for an extended time or cramping. Try taking slow, deep breaths to ease this pain.

After the procedure

You will stay at the center where you had the procedure for up to 2 hours. You must wait for the effects of the sedative to wear off. Because you received anesthesia or a sedative, you should not drive a vehicle or operate machinery. You should also avoid making 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 health care team

Before your colonoscopy, consider asking your health care team these questions:

  • Why do you recommend that I have a colonoscopy?

  • What will happen if I do not 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?

Related Resources

Types of Endoscopy

Cancer Screening

More Information

American College of Gastroenterology: Colonoscopy

National Institute of Diabetes and Digestive and Kidney Diseases: Colonoscopy