4 Polyethylene Glycol 3350 Side Effects You Should Know About

Polyethylene glycol 3350 (Miralax) is an over-the-counter (OTC) medication that treats occasional constipation. It’s also part of some kits that help you prepare for a colonoscopy procedure. But colonoscopy prep is an off-label use, meaning the medication is not approved for this purpose.

Polyethylene glycol 3350 is part of a group of medications called osmotic laxatives. They work by allowing water to be more easily absorbed into the stool. This helps stool pass more easily. 

The medication is a flavorless powder that can be mixed into any liquid. Most people will have a bowel movement within 1 to 3 days after taking it. You should stop taking it once you have a bowel movement.

Polyethylene glycol 3350 works well and doesn’t usually have serious risks. But like all medications, side effects are possible. We’ll cover four of the most important ones below, plus a few more tips.

1. Nausea

Nausea is a possible polyethylene glycol 3350 side effect. 

If you’re taking this medication to prepare for a colonoscopy, you’ll only have to take it once. You should drink polyethylene glycol 3350 slowly, and take a break if you feel nauseous or throw up. You can stop drinking the liquid for about 30 minutes to give your stomach a break. If you’ve thrown up, make sure to let your surgeon know.

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Put the liquid in the fridge until you’re ready to drink it again. While you’re taking a break, drink clear liquids to stay hydrated. When you’re ready to drink the medication again, using a straw may also help with nausea. 

If you’re taking polyethylene glycol 3350 for constipation, you may need to use it daily for up to 7 days depending on how long it takes to work. If you feel nauseous, try taking it with food to ease the nausea. 

2. Gas and bloating

Polyethylene glycol 3350 can cause some gas and bloating. But luckily, it’s less likely to cause this than other laxatives.

If you’re experiencing gas and bloating, you can try some things to help reduce these uncomfortable symptoms. These include:

• Avoiding carbonated beverages

• Avoiding FODMAP foods (foods that aren’t easily digested in the small intestine, including wheat, milk, and foods containing high-fructose corn syrup)

• Eating slower and sitting down when eating

• Having smaller (but more frequent) meals throughout the day

• Trying OTC medications like Gas-X (simethicone)

Gas and bloating are symptoms of constipation itself. So when your constipation is relieved, these symptoms may improve as well.

3. Allergic reactions

Polyethylene glycol 3350 may cause an allergic reaction in some people. Signs of an allergic reaction can include itching, rash, or hives. More serious signs include swelling of the face, trouble breathing, and vomiting. If you notice any serious signs of an allergic reaction, seek emergency care.

4. Severe diarrhea

Polyethylene glycol 3350 can treat constipation, but high doses can also cause diarrhea or make you go to the bathroom multiple times a day. Diarrhea from polyethylene glycol 3350 is more common in older adults. If you have persistent diarrhea after taking polyethylene glycol 3350, stop taking it and talk to your healthcare provider. It may be nothing to worry about, but it’s best for your provider to evaluate whether something else may be going on.

When should I contact my healthcare provider about side effects from polyethylene glycol 3350?

If you experience any mild polyethylene glycol 3350 side effects, like nausea or gas, you may be able to manage these at home with lifestyle changes or other OTC medications. But if you develop side effects like persistent diarrhea, contact your healthcare provider. While it may be nothing to worry about, it’s a good idea for them to evaluate whether something more serious is going on. 

If you have any signs of a severe allergic reaction, like swelling of the face or trouble breathing, seek emergency care.

Can you take polyethylene glycol 3350 every day?

You can take polyethylene glycol 3350 daily to treat constipation. But it should be stopped once you have a bowel movement. And it shouldn’t be used for more than 7 days total.

If you’ve taken polyethylene glycol 3350 for 7 days and you haven’t had a bowel movement yet, reach out to your healthcare provider. This could be a sign of a more serious problem.

Keep in mind that polyethylene glycol 3350 can be habit-forming. Don’t take a larger dose than recommended, or take it for more than 7 days.

Who shouldn’t take polyethylene glycol?

Children less than 17 years old, pregnant women, and people with kidney problems should talk to their healthcare provider before starting any OTC laxative, including polyethylene glycol 3350. And there are a few groups of people who should avoid polyethylene glycol 3350 altogether. These include people with:

• An existing blockage of the intestines (bowel obstruction)

• An existing tear in the wall of your bowels (perforated bowel)

• Inflammation of the appendix (appendicitis)

• Ulcerative colitis

• Crohn’s disease

• A previous allergic reaction to polyethylene glycol or any of the ingredients in the product

Why trust our experts?

Written by:

Nicole E. Cieri-Hutcherson, PharmD, BCPS, NCMP

Nicole E. Cieri-Hutcherson, PharmD, BCPS, NCMP, has over a decade of experience as a pharmacist, professor, and researcher. She was a full-time clinical professor in the pharmacy practice department at D’Youville School of Pharmacy before subsequently joining the faculty of the pharmacy practice department at the University at Buffalo School of Pharmacy and Pharmaceutical Sciences.

Edited by:

Amy B. Gragnolati, PharmD, BCPS

Amy Gragnolati, PharmD, BCPS, is a pharmacy editor for GoodRx. Amy currently holds her pharmacist license in Georgia and California.

Reviewed by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

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