How to Prepare Your Colon For a Colonoscopy

What you need to do in the days leading up to a colonoscopy

Roll of toilet paper
You will be spending a fair amount of time on the toilet during your colonoscopy preparation. Make sure you have proper supplies such as wet wipes, toilet paper, and a magazine. Suki Photography by Sandra Grimm/Moment/Getty Images

In order to have a successful colonoscopy, the body, and especially the large intestine (colon), must be properly prepared. Colonoscopy prep is an important part of the procedure that is usually done at home, following the directions given by a gastroenterologist. The preparation is often the most uncomfortable part of a colonoscopy because light sedation or "twilight sleep" is normally used during the procedure itself to prevent any discomfort. Most people will not remember what happened during the actual test (which is why it's important to bring a friend or family member along to talk to the doctor and to drive home).

What a Colonoscopy Is, and Why It's Done

A colonoscopy is a procedure that looks at the inside of the colon. This is done by inserting a flexible tube with a light on the end into the anus. A doctor can move the tube through the rectum and up into the colon to see inside and to look for polyps or other abnormalities. It's recommended that everyone over the age of 50 get a screening colonoscopy to check for colorectal cancer. Some people may need the procedure earlier, depending on risk factors for colon cancer.

A Colonoscopy Prep

The goal of the colonoscopy prep is to eliminate all fecal matter (stool) from the colon so that the physician that is doing the colonoscopy will have a clear view of the intestinal wall. There are several typical ways to get this done, and some doctors and patients will have their own unique methods that work best for them. Some of the main types of preparation are Golytely (also sold under the names Colyte, or Nulytely), and sodium phosphate tablets (Osmo-Prep and Visicol).

Colonoscopy Prep Tips

  • To reduce any anal discomfort, use adult wet wipes or a water spray to clean the rectal area instead of toilet paper.
  • Keep plenty of clear liquids on hand to drink. Water gets boring and staying hydrated is important.
  • Follow the doctor's instructions. You wouldn't want to have to do the prep all over again because you didn't get it right the first time.
  • Be prepared to spend most of the day before your test on the toilet. Bring a book.
  • Call the doctor's office for help if you have any trouble or don't understand the prep instructions.

Polyethylene Glycol–Electrolyte (Golytely, Colyte, NuLytely, TriLyte)

This preparation will require a prescription from the doctor. It consists of a gallon jug with a powder mix inside. The patient will fill the jug with water and mix in the powder to make a drink. The instructions are usually to drink one 8 oz glass of the mixture every 10 minutes until the entire gallon is finished or eliminations are clear. After the first few glasses, bowel evacuation (in the form of diarrhea) will begin. Before the gallon is finished, many people find that their evacuations are totally clear and all the stool is cleaned out of the colon.

If eliminations do not become clear after the gallon is finished, an enema may be needed. Some people do experience nausea when drinking so much liquid, so the physician may prescribe an anti-nausea medication in case it is needed. Golytely now comes in several flavors to make it more palatable and easier to drink.

Sodium picosulfate

This is a laxative that contains sodium picosulfate, magnesium oxide, and anhydrous citric acid. It comes in a powder that is taken mixed into water. Sodium picosulfate is a stimulant laxative and magnesium oxide  and anhydrous citric acid combine with water to form magnesium citrate, which is an osmotic laxative. This preparation is often given in 2 parts: one the night before and one the morning of the test. In some cases the doses might be given earlier in order to have the entire prep over and finished in time to leave for the test. The powder should be mixed with water right before it's time to drink it and not before. The laxative action of this prep will cause a lot of water to leave the body through the bowels so it's important to keep drinking enough water and other clear liquids to replace it.

Sodium phosphate

Sodium phosphate tablets are prescribed by the doctor doing the colonoscopy. There are two different brands, depending on which your doctor prescribes -- Visicol, a 40-tablet regimen, and Osmo-Prep, a 32-tablet regimen.

With Visicol, 7 doses are taken in 15-minute intervals: 3 tablets are taken for 6 doses, and then 2 tablets are taken for 1 dose (20 tablets total). The next morning, 3 to 5 hours before the test, the same dosage is repeated (3 tablets for 6 doses, and then 2 tablets for 1 dose, in 15-minute intervals for a total of 20 tablets).

The prep begins to take effect about an hour after the first dosage of tablets is taken. A liquid diet is usually prescribed starting about 12 hours before starting the regimen. Potential side effects include bloating, nausea, vomiting, and abdominal pain.

In Osmo-Prep (the newer form), the tablets are taken the evening before and the morning of the colonoscopy. The evening before the test, 4 tablets are taken with 8 ounces of a clear liquid every 15 minutes for a total of 5 doses (20 tablets total). The next morning, about 3 to 5 hours before the test, another 3 doses of 4 tablets are taken at 15 minute intervals (12 tablets total).

A Word From Verywell

There are a variety of preparations available and more are being developed because it's understood how difficult it is to undertake this part of a colonoscopy. Some physicians will have other ways of preparing and will offer instructions on how they've fine-tuned their procedures. In some cases, if patients have specific conditions that prevent the use of the laxatives, there are other ways to prepare. For people who have had surgery on the bowels, an full prep might not be needed, and there could be a modified version available. Work with the prescribing physician in order to determine what the best method will be in order to clean out the colon and be ready for the test.


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View Article Sources
  • UMHS Medical Procedures Unit MPU/MPC staff. "Colonoscopy." U-M Health System. June 2007. 
  • Jan Nissl, RN, BS. "Colonoscopy" Cigna. September 1, 2006. 
  • Lester Stine, MD. "Preparing for Colonoscopy." Three Rivers Endoscopy Center. 2004.
  • Salix Pharmaceuticals. "Visicol Product Information." Salix Pharmaceuticals 2004.
  • Salix Pharmaceuticals. "OsmoPrep Product Information." Salix Pharmaceuticals 2006.