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Family Health

Which Colonoscopy Prep Is Right for You?


Yale Medicine experts discuss new options for the requisite cleanse before a colonoscopy.

Most people would agree that a colonoscopy “prep” is rough, but what if part of the process could be more bearable? It turns out there are a few different prep options you may not know about.

While the goal remains the same—clearing your bowels so that your gastroenterologist can examine the inside of your colon to screen for cancer—you might be able to drink less of the required laxative drink (which many find has an unappealing taste), choose a better-tasting prep, or possibly take pills instead.

“The procedure itself is painless, but the prep is often considered the difficult part,” says Jeremy Matloff, MD, a Yale Medicine gastroenterologist. “The good news is that many of the preps available today are much easier than what was used years ago.”

Colonoscopies save lives, adds Daniel Lavy, MD, a Yale Medicine colorectal surgeon. Colorectal cancer is the third most common cancer in the United States and has been on the rise in younger people. Colorectal cancer is the leading cause of death from cancer in men and second in women under age 50.

During a colonoscopy, patients are put under sedation, and a long, flexible tube with a camera at the tip is inserted through the anus and into the rectum and colon. The doctor identifies, removes, and, in some cases, biopsies any abnormalities, such as polyps (abnormal growths that could turn into cancer). The laxative prep used to clear out the colon before the procedure is important because any stool left in the colon can hide polyps and small cancers.

The American Cancer Society and the U.S. Preventive Services Task Force recommend those who are at average risk for colorectal cancer should be screened every 10 years between ages 45 and 75. If someone is at increased risk for colorectal cancer, for example, because of family history, more frequent screening may be recommended.

Below, we talk more with Drs. Matloff and Lavy about the different types of colonoscopy preps available today and how to decide which one is best for you.

How is a colonoscopy prep traditionally done?

In the past, the standard method, which is still used by many doctors’ offices, entailed drinking up to 4 liters (nearly a gallon) of a prescribed drink solution and water. These traditional preps are polyethylene glycol (PEG)-based. PEG is an osmotic laxative, which means it draws water from the body into the stool to create softer, easier, and more frequent bowel movements—all of which are needed to effectively empty the colon, providing the endoscopist with a clear view to identify any abnormalities during the procedure.

PEG-based preps come in different flavors and are mixed with a large amount of water. They usually contain electrolytes or are consumed with an electrolyte drink to avoid dehydration caused by fluid loss when the colon empties. Many say the preps have a salty taste. PEG-based preps include GoLYTELY, MiraLAX, and MoviPrep. There are also sulfate-free PEG preps that some people prefer because they taste a little less salty. A few of these brands include NuLYTELY and TriLyte. (More details on the prep process below.)

Typically, it takes one to three hours for the laxative prep to kick in—and then the visits to the bathroom begin.

What’s more, the sheer volume of liquid required with this prep can be difficult for patients to tolerate, Dr. Matloff says.

What is a ‘split’ colonoscopy prep?

In the past, most patients were directed to do their prep the night before their colonoscopy. But now, many doctors offer what is known as a “split” prep, meaning patients take half of their prep the night before the colonoscopy and the other half the morning of the procedure.

This option is common for morning colonoscopies. For afternoon procedures, a patient may do a single-dose prep the morning of the procedure—or still do a split prep, but start the prep later the night before the procedure.

“Studies have shown that the split preps are better for patients and allow the physician to see the inside of the colon more clearly,” Dr. Lavy says.

So, if you are using GoLYTELY, for example, at 6 p.m. the night before the colonoscopy, you would drink 8 ounces of the prep (which is mixed with water) and continue to drink 8 ounces every 10 to 15 minutes until the 4-liter bottle of GoLYTELY is half empty. On the morning of the procedure (three to five hours before arriving at the doctor’s office), you do the same thing as the night before, until the remaining 2 liters of solution are gone.

What is a ‘lower volume’ colonoscopy prep?

In the last 10 to 15 years, what’s known as “lower volume” preps have become options. These are saline-based formulas and contain sodium phosphate (NaP) as the primary osmotic agent, as well as other minerals, such as potassium and magnesium. Some patients say these preps taste much better than the traditional ones—some even compare them to a sports drink. They also come in a pill form. They require drinking 2 to 3 liters of fluid instead of 4 liters.

Saline-based preps include SUPREP®, Clenpiq®, and Sutab® (the tablet form). SUPREP was approved by the Food and Drug Administration (FDA) in 2010; Clenpiq and Sutab were approved in 2017 and 2020, respectively.

If you are doing a split-dose prep, the night before the procedure, you pour one bottle of SUPREP, for example, into a mixing container and then fill it with water to the 16-ounce line. You mix it, drink it, and then drink an additional 32 ounces of water over the next hour. The next morning (10 to 12 hours after the evening dose and three to four hours before the procedure), you repeat the entire process.

“Patients have to drink a lot of water, but the amount of the actual prep solution they have to drink actually isn’t that much,” Dr. Matloff says. “And people obviously prefer to drink more water than prep.”

Pills for prep: how it works

The first thing to know about the pill route for colonoscopy prep is that it’s a lot of pills: 24, to be exact. However, as mentioned earlier, many doctors have patients take 12 pills the night before the procedure and 12 more the morning of it if they are doing a split prep.

Plenty of water is needed to go with those pills. Dr. Lavy adds. For example, if you are using Sutab, the night before the procedure, you take one pill with a sip of water every 1 to 2 minutes (16 ounces of water total) until you’ve taken 12 pills. You then drink an additional 32 ounces of water over the course of an hour. These steps are repeated on the morning of the procedure.

Which colonoscopy prep is right for me?

While some doctor’s offices have a preferred method of prep, many work with their patients based on their needs, or some offices might offer patients several choices.

It’s also important to note that the salts from the NaP preps can irritate your intestinal mucosa if you have an inflammatory gastrointestinal disease. NaP formulas also might not be the best option for those at risk of complications from fluid-electrolyte shifts, as well as for those who have certain pre-existing conditions or who take certain medications.

“For example, someone with chronic kidney disease might have electrolyte imbalances that would mean one prep is better than another, and your doctor should go over all of that with you,” Dr. Matloff says. “Or some people prefer the pills because the taste of the liquid prep is a limiting factor for them.”

Sometimes, insurance coverage can be an issue with the pills or other specific preps, Dr. Matloff says. But they typically cost less than $50.

“All preps have various nuances, but if we can give patients easier options that fit their individual preferences, it increases the chances they’ll have a successful colonoscopy,” Dr. Matloff says. “And that will lead to more lives saved.”