What Are the Worst (And Best) Colonoscopy Preps? Don't Pooh-Pooh This Article

By Josh Bloom — Apr 09, 2021
Last week, it was colonoscopy time again. Oh, joy! But it gave me an excuse to look up alternate bowel preps – and it's a damn good thing I did. Which prep is the one to have? Which is best to avoid? It's not so easy to tell. As a bonus, here are some hilarious quotes.
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If you're lucky enough to have died at age 49, there is no need to read this. But if you reach 50, welcome to the beginning of old age, where icky things start to happen to you. One icky but hugely important thing will be a birthday gift called a colonoscopy, which people fear mightily. They shouldn't. Although the image of a bassoon being force-fed into your anus isn't especially comforting, a colonoscopy is nothing more than a really good nap, thanks to the wonder drug propofol, something I wrote about in 2020

The real problem is a second gift that necessarily precedes the first - the dreaded colonoscopy prep, and it doesn't even come with a card. If you don't like it (you won't), don't worry. You can always return it. Check that.  You will return it, forcefully, but this transaction should not take place at the pharmacy.

Not all colonoscopy preps are equal. They range from "not that hideous" to "violation of the Geneva Convention hideous." The "good" news is that you do have some choices, which is made clear in a 2019 prospective study published in the Journal of Gastroenterology, which looked at the most commonly used bowel preparations (emphasis mine):


GoLYTELY significantly underperformed in terms of prep tolerability compared with magnesium citrate, MiraLAX with Gatorade, MoviPrep, OsmoPrep, Prepopik/Clenpiq, and SUPREP. 

Philip Gu, M.D., at. al.,  Am. J. Gastroenterol 2019 Feb 01;114(2)305-314, 

Do these findings match what patients have to report on askapatient.com – the website I go to before I try a new medicine? The patient ratings and rants are descriptive and subjective, not scientific. Nonetheless, if you look up a drug and its rating is below 2.5 or 3.0 out of 5, and there are some real doozies in the comments section, it's a pretty good bet that it's going to be all kinds of nasty. (See "4 Prescription Drugs People Hate" if you don't believe me.) 

I'm going to use patient ratings as a (very) rough indicator of what our choices are now and whether they are any better or worse than GoLYTELY, the gold standard of putridity – Four gallons of a vile salty-cherry tasting abomination that most of us (especially in the "almost time for a dirt nap crowd,") have either experienced or heard someone else complain bitterly about. Are the preps in the study, which are allegedly superior to GoLYTELY, really any better, at least when it comes to self-reporting of a few dozen to a few hundred people? 


GoLYTELY consists of polyethylene glycol 3350 aka PEG 3350 (no flavor), as well as sodium sulfate (salty flavor), sodium bicarbonate (salty flavor), potassium chloride (really nasty salty flavor), and sodium chloride (salt). Can it be the least bit surprising that victims patients who have taken the stuff have complained about the salty flavor?? 

If you're looking for amusing and creative quotes about the side effects of just about any drug website askapatient.com wins hands down. It did not disappoint...

"I thought it tasted like a lobster's urine would, with the same thickness/filminess." 

The salty flavor is only one problem with this vile potion. The volume that must be consumed – more than one gallon – is even worse. Here are the instructions on the label (emphasis mine):

"Fill the supplied container containing the GoLYTELY powder with lukewarm drinking water to the 4-liter fill line • Do not add any other ingredients, flavors, etc. • After capping the container, shake vigorously several times to ensure that the ingredients are dissolved. • Drink at a rate of 8 ounces every 10 minutes until the entire contents are consumed or the rectal effluent is clear. A loose watery bowel movement should result in approximately one hour."

Can you drink 8 ounces of saltwater every 10 minutes?? It actually sounds worse once we do the math. Since 4 liters = 135 ounces, at the rate of 8 ounces every 10 minutes, something that might be a challenge for a beluga whale, you would have to keep this up for 169 minutes (2 hours and 48 minutes), during which time you will have consumed 17 glasses of the stuff. 

Not surprisingly, some people had a bit of trouble (1). Including this unfortunate individual who didn't even make it past the starting line:

"After the first swallow, it came back up just like that scene in The Exorcist."

I stumbled upon some other amusing opinions... 

"Can I just suck on a piece of burnt rubber between 2 slices of toast? I'm sure that would taste better."

"Vile-tasting swill, chemically-induced cholera."

But for the people who could get it down, it works rather well...

"Let's just say my car's driver seat is in bad shape at the moment."

And even better, some elegant prose for your entertainment:

"Trying to clench my butt cheeks tightly together to avoid the fecal river that I knew was waiting to meander out of my anus." (My personal favorite)

The study concludes: "The bowel preps with the best bowel cleansing and tolerability were MiraLAX with Gatorade, MoviPrep, and SUPREP under real-world conditions." I was a bit surprised to find that patient comments and ratings – admittedly unscientific – don't agree with the study

SUPREP Bowel Prep Kit - Ask A Patient Avg. Rating 2.1/5

SUPREP contains a bunch of salts, some the same as in GoLYTELY and some different. It's still plenty salty. Is this a better recipe? I don't know, but the total volume the one must consume (3 liters) isn't that different than GoLYTELY (4 liters). And the patient ratings and comments might even be worse. For example...

"I'd rather someone inflate me with a fire-hose than drink this trash."

For those of you who have a life who are not familiar with Ask a Patient, it is very difficult to come up with a score that low. Even though I did a pretty thorough search while writing the "4 Drugs" article, I only came across one drug with a rating lower than 2.1, and it was significantly lower. Anyone want to guess?

MoviPrep - Ask A Patient AVG. Rating 2.6/5

MoviPrep is a similar concoction that contains polyethylene glycol and six different salts. The taste isn't any better, but at least you don't have to drink as much.

"Vile tasting. I gagged on the first sip. I will never use this product again."

But also...

"It is easier than Go Lightly [sic] because it's less volume--but still is disgusting!!"

Miralax - Ask A Patient Avg. Rating 3.4/5

Miralax contains only one ingredient - polyethylene glycol, aka PEG 3350 – a white powder that dissolves in water and gives something that is virtually indistinguishable from a glass of water. As a colonoscopy prep, it is dissolved in Gatorade. You damn well better like Gatorade because you'll be drinking two 32-ounce bottles of it. That's a bitchload of Gatorade, and after that, you're supposed to drink 16 ounces of water. Even with these volumes, it still adds up to a slightly lower volume than Go Lightly. Because there are no salts (2) other than those present in the Gatorade, it tastes exactly like the Gatorade. Of the four preps in this article, Miralax got the highest rating, 3.4/5.

But this rating doesn't mean much because most (~90%) of the reviewers took Miralax for other conditions, for example, constipation or IBS. The poor ratings were generally due to cramping and diarrhea, not the taste. Some people reported severe vomiting. 

My Own Experience

Miralax worked very well. Mixed with Gatorade, I was able to drink all 64 ounces with little trouble.  I then hydrated the rest of the day. No significant issues (3,4). More or less. Miralax is used with Dulcolax (maybe the smallest pills I've ever seen), but also a 10-ounce bottle of magnesium citrate (not rated). The first sip: "Hey, this stuff ain't bad. It tastes like lemon soda!" By ounce #5: "Maybe not." By ounce #9: "Make that Lemon Pledge with rock salt in it." OK, it wasn't wonderful, but most people shouldn't have much trouble, especially if you add ice. 

Bottom (heh heh) Line

It pays to do your homework. When my gastroenterologist suggested MoviPrep I pulled out a chainsaw politely declined since I wanted to go the Miralax/Gatorade route. He had no problem with it. The prep worked out just fine, and the next day when the magnificent propofol hit my blood, all I remember is waking up with an uncontrollable urge for Dunkin Donuts. 

It should be obvious that different people will have their own "favorites," and while the patient ratings don't agree with the clinical study, keep in mind that the study was scientific and the comments and ratings are not.

What's really important is that there are more choices now, which should help with prep day. Colonoscopy is very effective in detecting and removing intestinal polyps, which can become cancerous. Almost 50,000 people will die from colorectal cancer in a given year. Why be one of them?


(1) Others had no problem with GoLYTLEY and gave it good ratings. The numbers were all over the place.

(2) This makes a big difference. The complaint I saw time after time with all the formulas (except Miralax) was the salty taste. 

(3) I'll leave out hitting my head on the bathroom ceiling. 

(4) Use a straw to drink the stuff. It helps.

Josh Bloom

Director of Chemical and Pharmaceutical Science

Dr. Josh Bloom, the Director of Chemical and Pharmaceutical Science, comes from the world of drug discovery, where he did research for more than 20 years. He holds a Ph.D. in chemistry.

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