How to Properly Prepare for a Colonoscopy

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Preparing for a colonoscopy may be the most dreaded component of this invaluable screening test, but it's extremely important in order for the procedure to be effective. Proper colonoscopy preparation makes your colon squeaky clean, allowing the doctor to visualize the inner lining. Leftover stool or fluids can camouflage a tiny polyp or a section of irregular flat tissue within the colon. The cleaner your colon is, the better your doctor will be able to see.

Preparing for Your Colonoscopy

You may be dreading the preparation for a colonoscopy because you'll have to spend the majority of it in or near the bathroom evacuating your bowels. The prep consists of taking laxatives and substances that force a bowel movement (or many of them).

If you don't follow the prep instructions, there's a chance your test will be canceled. Let your doctor know right away if you cannot complete the prep so you can avoid no-show charges if your colonoscopy is canceled, or in case you'll have to have another one. In some cases, there's even a chance that the leftover stool may be confused with unhealthy tissue.

Every doctor orders a slightly different version of the colonoscopy prep, which will vary according to his or her preferences and your health. Some preps may begin with a liquid diet days before your test; others could involve using an enema and laxatives at home the night before. If you have questions, don't wait until the last minute—call the doctor’s office and get clarification.

Various Prep Options

Colonoscopy preps may consist of pills, liquids to drink (solutions), enemas to use rectally, or a combination of the three, along with dietary modifications. Oral laxatives come in the form of a pill or a liquid to drink and are commonly used in conjunction with a clear liquid diet. Some commonly prescribed pills and solutions include:

  • Dulcolax (bisacodyl) tablets
  • Magnesium citrate tablets or solution
  • Senakot (senna) tablets
  • GoLYTELY solution
  • NuLYTELY solution
  • TriLyte solution
  • Glycolax solution
  • CoLyte solution
  • Miralax solution
  • TriLyte solution
  • Fleet Phospho Soda (sodium biphosphate and sodium phosphate) solution or tablets

Preparation and Directions

These solutions may come in individual bottles or as do-it-yourself powders that need to be mixed. You should receive instructions on how to use the solution from your doctor. You will need to know exactly how much to drink and how often to drink it. Most of the older solutions, such as the GoLYTELY prep, are still reliable and widely used but require drinking a vast amount of fluids (up to four liters). Newer solutions may require less formula to drink, but you will still need to drink plenty of water to flush the colon clean.

Solution Taste

The bitter and salty taste of some solutions can stop the prep in its tracks. However, many of the newer formulas are sulfate-free, which means they don’t have a salty aftertaste. If you can’t tolerate the solution, there's not a lot of chance that you're going to drink all four liters. Ask your doctor about the pre-flavored mix options, which may include cherry, lemon-lime, or even a pineapple taste additive. If your taste buds are still offended, ask your doctor if you can add a powdered commercial drink prep, like Crystal Light or Gatorade, to mitigate the flavor.


Enemas are sometimes ordered to complete the colon cleansing prep, but can only clean out a small section at the end of the colon. Your doctor may order a tap water or Fleet enema for the night before or the morning of your colonoscopy. You will have to stay close to a bathroom after using the enema because they usually work very quickly (within 10 minutes or less).

Dietary Prep

Some colonoscopy preps may include a dietary change for one to four days before the procedure. This diet will consist of clear liquids only—if you can see through it, you can probably eat or drink it. Some favorites on the clear liquid diet include beef or chicken broth, clear sodas, white grape or apple juices, and gelatin. Avoid red and purple gelatin or sports drinks, as they can tint the colon. Unless your doctor tells you otherwise, you can continue to drink tea or coffee, but hold the cream or milk. If you're getting hungry on your clear liquid diet, consider drinking a tall glass of water with every "meal."

Prior to, or in lieu of, a clear liquid diet you may be put on the low-residue diet. This diet consists of meal replacement shakes, soups, or bars, which are mostly protein and calories with very little fiber (residue). You should not eat any fruits, vegetables, or grains on the low-residue diet.

Comfort Measures

The colonoscopy prep has one more concerning issue: the side effects of rapidly discharging the colon. The substances used to clean your bowels may stimulate some unpleasant side effects, such as explosive gas and nausea. Your doctor may prescribe medications to help with these symptoms, including:

  • Reglan (metoclopramide): Helps move the prep substances through the stomach quickly, which can help alleviate nausea and heartburn.
  • Mylicon, Gas-X, Mylanta (simethicone): Helps break up gas so that it can be passed more comfortably.

Take another proactive step toward comfort and invest in some quality toilet paper before your prep. Cheaper brands tend to be more abrasive and can irritate the skin around your anus after multiple trips to the toilet. Talk to your doctor if you have hemorrhoids and prepare accordingly with soothing baths, soaks, and creams as directed.

Other Potential Prep Side Effects

Other side effects, although uncommon, may include a fluid and electrolyte shift. Your body is constantly working to keep a balance between the fluids in your cells and the fluids in your bloodstream with the help of electrolytes, such as sodium or potassium. If you lose a lot of fluids at once (think frequent, watery stools) your fluid and electrolytes can get out of whack and cause uncomfortable symptoms, like a headache. Abdominal discomfort and vomiting are also uncommon but possible. If discomfort or symptoms are keeping you from completing the colonoscopy prep, call your doctor. He or she may have some suggestions to help increase your comfort level.

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