Approved by the Cancer.Net Editorial Board, 12/2019

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

A colonoscopy is a way for your doctor to see the entire large intestine. It can help find the cause of problems in a part of the intestine called the colon. Doctors also use it to check for colorectal cancer.

About the large intestine and colon

The large intestine is a major part of your digestive system. It helps your body process the food your body does not use, which becomes waste. The colon is the biggest part of your large intestine. It empties into the rectum, where waste collects as bowel movements. The rectum empties into the anus, where bowel movements leave the body.

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

Your doctor places a thin, lighted tube through your anus and rectum up into the colon. Before the procedure, you get a sedative and pain medication to make you more comfortable. The colonoscopy tube has a small camera on it. It shows your doctor images of the inside of your colon as the tube moves through. The doctor can also take a small sample of tissue through the tube to examine later. Getting this type of sample is part of a test called a biopsy.

Who does my colonoscopy?

A doctor called a gastroenterologist, or GI doctor, usually does a colonoscopy. This type of doctor specializes in the digestive system.  A surgeon may also do the procedure. Your team will also include a nurse and possibly an anesthesia specialist.

Getting ready for a colonoscopy

You will probably have your colonoscopy at a doctor's office or hospital. Getting ready is important, because your colon needs to be as clean as possible. This will allow the doctor to see the colon well. So when you schedule your colonoscopy, you will get detailed instructions on how to prepare.

Here are some things to keep in mind:

  • Tell your doctor about all the medications you take, including any vitamins, herbs, or supplements. Be sure to ask if you should take them on the day of the test. If you take a blood thinner or daily aspirin, you might need to stop several days before the procedure.

  • Tell the doctor about any drug allergies or medical conditions you have.

  • You will need to avoid solid food for 1 to 3 days before the procedure. You may drink clear liquids up to a certain time. These may include fat-free bouillon or broth, black coffee, strained fruit juice, or gelatin.

  • You will need to take a laxative or give yourself an enema at a certain time before the colonoscopy. Your doctor's office will tell you what to use. The laxative is a pill or a powder you mix with water before drinking. A laxative speeds up the process of waste leaving your colon and it will make you have more bowel movements than usual. 

  • Arrange for a friend or family member to drive you home. You will be sleepy after the procedure.

  • Check your insurance coverage. Make sure it covers the medical center where you will have the test, the doctor who will do the colonoscopy, and the anesthesia doctor who will give you the sedative.

  • You will be asked to sign a consent form before your colonoscopy. It will state that you understand the risks and benefits of the colonoscopy and agree to have it. Your doctor or nurse will explain the procedure before you sign the form, and you can ask questions.

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. When you get to the hospital or doctor's office, you will change into a hospital gown. You will be in a private room with a sheet draped over your body.

The nurse or anesthesia specialist will give you pain medication and a sedative. You will get this through an intravenous tube, or IV. The IV goes in a vein in your arm. You might feel a small sting from the IV needle when it goes in.

To start the procedure, the doctor blows some air through the small tube into your colon. This inflates the colon slightly so the doctor can see better. You might need to change your position during the procedure. This is to help the doctor move the colonoscopy tube or get a better view. If you are asleep, the doctor or nurse will help with this.

If you have an abnormal growth, or polyp, in your colon, the doctor will remove it. Or they may take a small sample of tissue. This is not usually painful, and the doctor will stop any bleeding. If the growth is too large or complicated to remove during the colonoscopy, doctors may remove it later.

During the procedure, you may feel discomfort from lying still for a long time. If you are awake, you may have some cramps. If so, tell your nurse. You can also take slow, deep breaths to relax.

There is a small risk that the tube used for a colonoscopy might puncture the colon. This is rare, but you might need surgery to repair it if this happens. Talk with your health care team if you have concerns about this.

After the procedure

You will stay at the hospital or doctor's office until you are fully awake. You should not drive a vehicle, operate machines, or make important decisions the rest of the day. A friend or family member can drive you home.

You can expect to go back to normal activities the next day.

Contact your doctor immediately if you have:

  • Severe abdominal (belly) 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 one?

  • Who will do the colonoscopy?

  • What will happen during the procedure?

  • How long will it take?

  • Will it hurt?

  • Will I get medication to make me more comfortable?

  • What are the risks and benefits of a colonoscopy?

  • Can I take my regular medications the day of the procedure? Which ones should I not take? When can I take them again?

  • How do I find out what the procedure will cost me?

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

  • When will I learn the results?

  • Who will explain the results to me?

  • Will I need more 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