Miralax (Polyethylene Glycol 3350) - Oral

What Is Miralax?

Miralax (polyethylene glycol 3350) is an over-the-counter osmotic laxative used to treat constipation. Constipation is characterized as having fewer than three bowel movements a week. Miralax helps treat constipation by allowing the stool to hold more water and pass through the colon. 

Miralax comes in powder form, which must be mixed in a beverage to dissolve. 

Drug Facts

Generic Name: Polyethylene glycol 3350

Brand Name: Miralax, GaviLAX, GlycoLax

Drug Availability: Over the counter

Therapeutic Classification: Osmotic laxative

Available Generically: Yes

Controlled Substance: N/A

Administration Route: Oral

Active Ingredient: Polyethylene glycol 3350

Dosage Form: Powder for solution, packet

What Is Miralax Used For? 

The Food and Drug Administration (FDA) approved Miralax for short-term use to treat occasional constipation.

Occasional constipation is defined as intermittent or periodic changes in bowel habits, such as fewer bowel movements and difficulty passing stools. These symptoms may last for a few days or weeks. Often, occasional constipation can be treated with OTC laxatives or bulking agents, in addition to lifestyle and dietary changes.

Miralax (Polyethylene Glycol 3350) Drug Information - Illustration by Zoe Hansen

Verywell / Zoe Hansen

How to Take Miralax

To take Miralax, measure the amount of powder in the attached cap. The dose is 17 grams each day. Mix the powder with 8 ounces of a hot or cold beverage, such as water, coffee, or juice. If using individual-dose packets, mix one packet with 8 ounces of liquid. Stir the powder and liquid mixture to dissolve the powder, and then drink it immediately.

Take once a day as needed, and do not take for longer than one week without your healthcare provider’s instruction. You can take it at any time of the day. 


Store Miralax in its original container. Keep dry and at room temperature (between 68 F and 77 F). 

How Long Does Miralax Take to Work?

It may take Miralax anywhere from two to four days to produce a bowel movement.

What Are the Side Effects of Miralax?

This is not a complete list of side effects, and others may occur. A healthcare provider can advise you on side effects. If you experience other effects, contact your healthcare provider. You may report side effects to the FDA at fda.gov/medwatch or 1-800-FDA-1088.

Miralax may cause some side effects. These side effects are associated with the way Miralax works to treat constipation. 

Common Side Effects

The most common side effects include:

  • Nausea
  • Gas
  • Abdominal bloating
  • Abdominal cramping

Severe Side Effects

Miralax does not commonly cause severe side effects, but it may cause:

If you experience severe diarrhea or hives, stop taking Miralax and contact your healthcare provider. If you feel that symptoms are severe or life-threatening, call 911 or go to the nearest emergency room for evaluation.

Long-Term Side Effects

If Miralax is taken too often or for too long, it may become habit-forming. Take only as directed. 

Report Side Effects

Miralax may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your healthcare provider may send a report to the FDA's MedWatch Adverse Event Reporting Program or by phone (1-800-332-1088).

Dosage: How Much Miralax Should I Take?

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The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For oral dosage form (powder for solution):
    • For constipation:
      • Adults and children 17 years of age and older—17 grams (g) once a day.
      • Children younger than 17 years of age—Use and dose must be determined by your doctor.


If you are pregnant or nursing, contact your healthcare provider before taking Miralax.

You should also talk to your healthcare provider before using Miralax if you have a history of intestinal blockage.

Missed Dose 

Miralax is taken as needed, and no missed dose instructions are required.

Overdose: What Happens If I Take Too Much Miralax?

Symptoms of a Miralax overdose may include diarrhea, excessive thirst, confusion, or seizures. Dehydration due to diarrhea might occur if you aren’t drinking enough fluids. If you have taken too much Miralax, stop taking the medication and drink plenty of water. 

What Happens If I Take Too Much Miralax?

If you think you or someone else may have overdosed on Miralax, call a healthcare provider or the Poison Control Center (1-800-222-1222).

If someone collapses or isn't breathing after taking Miralax, call 911 immediately.


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If your or your child's constipation do not improve within 7 days, or if they become worse, check with your doctor.

What Are Reasons I Shouldn’t Take Miralax?

Do not take Miralax if you are allergic to any of its ingredients or have a known or suspected bowel obstruction. It should also not be used in people with kidney disease unless approved by their healthcare provider.

What Other Medications Interact With Miralax? 

Miralax may interact with a heart medication called digoxin. It is important to talk to your healthcare provider if you take digoxin and want to take Miralax.

Other drug interactions may occur. To prevent potential interactions, tell your healthcare provider or pharmacist about all prescription and OTC drugs, vitamins, and herbal supplements you take before starting Miralax.

What Medications Are Similar?

Other osmotic laxatives work similarly to Miralax, such as:

  • Magnesium citrate or milk of magnesia
  • Sodium phosphate
  • Lactulose

Miralax generally causes a bowel movement to occur within three days. A magnesium laxative may produce a bowel movement more quickly if needed. 

These drugs are also used to treat constipation, and it is not recommended to take them with Miralax. Talk to your pharmacist or a healthcare provider if you have questions.

Frequently Asked Questions

  • What is Miralax used for?

    Miralax is used to treat constipation, generally described as having fewer than three bowel movements a week.

  • How does Miralax work?

    Miralax works by allowing water in the body to move into the stool in the colon. The water helps the stool soften and move through the colon easier.

  • How long does it take for Miralax to work?

    It can take Miralax anywhere from two to four days to produce a bowel movement.

  • How long can I take Miralax?

    Miralax is meant to be taken only for occasional constipation, usually for no longer than one week. If you need constipation treatment longer than that, talk to your healthcare provider.

How Can I Stay Healthy While Taking Miralax?

It is important to make sure you’re drinking an adequate amount of water and eating a diet rich in fiber. How much fiber to eat may depend on your age and sex; recommended fiber amounts for adults range from 22 to 35 grams per day. If you're having trouble getting enough fiber in your diet, consider consulting a registered dietitian nutritionist to come up with a fiber-rich eating plan that works for you.

Additionally, drinking enough water and other liquids can help soften your stools, making them easier to pass. You can also get liquids through foods like sweetened fruit and vegetable juices and clear soups.

These strategies can work together to manage constipation and help you have regular bowel movements. However, if you continue to struggle with bowel movements, talk to your healthcare provider about other options.

Medical Disclaimer

Verywell Health's drug information is meant for educational purposes only and is not intended to replace medical advice, diagnosis, or treatment from a healthcare provider. Consult your healthcare provider before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. DailyMed. Label: Miralax- polyethylene glycol 3350 powder, for solution.

  2. MedlinePlus. Polyethylene glycol 3350.

  3. Rao SSC, Lacy BE, Emmanuel A, Müller-Lissner S, Pohl D, Quigley EMM, Whorwell P. Recognizing and defining occasional constipation: expert consensus recommendations. Am J Gastroenterol. 2022. doi: 10.14309/ajg.0000000000001945.

  4. North American Society for Pediatric Gastroenterology, Hepatology, Nutrition. Polyethylene glycol 3350 (PEG 3350) frequently asked questions.

  5. National Institute of Diabetes and Digestive and Kidney Diseases. Eating, diet, & nutrition for constipation.

Additional Reading

By Julie Scott, MSN, ANP-BC, AOCNP
Julie is an Adult Nurse Practitioner with oncology certification and a healthcare freelance writer with an interest in educating patients and the healthcare community.