Polyethylene Glycol: From colon prep to trusted laxative

Last month, I received a letter in the mail from my local gastroenterology clinic, reminding me I was due for a screening colonoscopy and to please call them at my earliest convenience. When I called, the scheduler asked me to call back again in a few weeks, when they hoped to resume scheduling non-urgent procedures.

Honestly, I felt a sense of relief. I don’t mind having the colonoscopy; it’s the preparation for it that’s hard to swallow. I am talking about that gallon container with powder in the bottom, named Go-Lytely® or Co-Lyte®, also known as polyethylene glycol or PEG 3350. Starting the day before your procedure, you add water, shake well, then drink the entire contents, one glass at a time. Glass after glass after glass…ugh. As a pharmacist, I’ve dispensed hundreds of those gallon jugs.

First-time users often ask, “What does it taste like?”

“Like flat mineral water,” I answer.

“Can I flavor it?”

“Sure, as long as you don’t use anything red, orange, or purple.”

“What flavor would you recommend?”

“Well, I suggest you don’t use your favorite flavor because, by the time you’re done, it won’t be your favorite flavor anymore.”

The last time I had to drink Go-Lytely®, I watched the movie The Proposal with Sandra Bullock, putting it on pause when I needed a bathroom break. I still smile when I think of Betty White dancing around, wearing that crazy cape! PEG 3350 and glycerin are osmotic laxatives. They work by creating a concentrated solution inside your intestine that attracts water. Pulling this extra water into your intestine increases the water in your feces. This will soften your stool and help move it along. PEG 3350 is polyethylene glycol, part of a large family of compounds ranging from liquids to oily solids.

Each PEG has a number that describes how big the molecule is. PEGs range from PEG 400, which is liquid, to PEG 20,000, an oily solid. PEGs are one of the most common ingredients in your home. Most detergents, antifreeze, printing inks, adhesives, resins, and lubricants contain some form of PEG. You’ll also find them in cosmetics like lipsticks, creams, lotions, and powders. PEGs are also used in pharmaceutical manufacturing, including ointments, tablets, suppositories, and solvents for certain injectable medicines. Because PEGs are broken down by enzymes found in micro-organisms. They are often added to plastic products to improve biodegradability.

PEG 3350 is a safe, powerful laxative that isn’t limited to use as a gallon of colon preparation. It’s also available as the nonprescription product Miralax®. Whether you use a full scoop from the can or open a single serving packet, the usual dose is 17 grams mixed with 4-8 ounces of fluid. You can mix the powder into any liquid and flavor it however you like. A single dose of Miralax can start working within an hour or so but is more likely to give you a bowel movement in one to three days.

Another laxative that works like PEG is glycerin. Glycerin is often used as a rectal suppository in children suffering from constipation. Glycerin suppositories work in the lower colon and rectum. They can give you relief from constipation within 30 minutes, much faster than Miralax®. Glycerin and PEG 3350 do their job while staying inside your intestines, which is one reason they are considered very safe to use. Side effects of PEG 3350 are usually mild, like gassiness, an upset stomach, or bloating and abdominal cramping.

Here are 4 Tips on Using Osmotic Laxatives Successfully:

1. Keep ‘em cool. Suppositories are designed to melt at body temperature. Years ago, I forgot about the light fixture directly underneath the shelf of my medicine cabinet, where I stored a bottle of prescription-only nausea suppositories. Just when I REALLY needed one, all I found was a goopy, melted mess.
2. Chill it. When drinking an entire gallon of PEG 3350, the taste can start to get to you. Mixing it up the night before and refrigerating it can help the flavor. Remember, you can not dilute the colon prep PEG 3350 with ice or water.
3. Mix and Match. Another way to help you drink ALL of your colon prep is to divide it up and use different flavors for each. This way, you don’t get as tired of it.
4. Red Means Stop. When preparing for a colonoscopy, you MUST avoid any red or purple drinks or foods. Lemon, lime, or pineapple can be used, or any flavor of Crystal Lite that isn’t red.

Dr. Louise Achey, Doctor of Pharmacy, is a 43-year veteran of pharmacology and author of Why Dogs Can’t Eat Chocolate: How Medicines Work and How YOU Can Take Them Safely. Get clear answers to your medication questions at her website and blog TheMedicationInsider.com. ©2022 Louise Achey