How Fast Does Miralax Work? - Walrus Health

Questions Articles Drugs Ask a pharmacist How Fast Does Miralax Work?

In our latest question and answer, our pharmacist discusses how long it takes for Miralax (polyethylene glycol) to begin working.

Answered By: Dr. Brian Staiger Pharm.D Nov 22, 2017

Hearns asked

How fast does Miralax work? I need to use it for constipation and want to know if works faster than other products.

Answer

Miralax (polyethylene glycol) is classified as an osmotic laxative and bulking agent for the treatment of occasional constipation. At usual doses, Miralax will begin to work in 12 to 72 hours. It works by binding water, causing it be retained within the stool. Additionally, it increases the weight of the stool, softens stool consistency and overall facilitates ease of fecal evacuation.

Miralax, when taken in doses used for constipation, does NOT quicken transit time in the gastrointestinal tract, unlike stimulant laxatives (which stimulate muscle contractions in the intestines). This is why Miralax has such a wide range of onset of action. However long it takes a particular individual to pass a bowel movement is generally close to the onset of action of Miralax.

Miralax is a great option for the relief of occasional constipation due to the lack of side effects. It is not absorbed by the body and does not cause tachyphylaxis (i.e. diminishing effects with overuse) as many stimulant laxatives do.

It is important to note that Miralax can be used for bowel evacuation prior to a colonoscopy in addition to relieving of occasional constipation. The usual dose of Miralax for constipation is 17 grams (one capful) in 8 ounces of liquid. This is the dose that will begin to work in 12 to 72 hours. When used for a colonoscopy prep, much higher doses are needed in conjunction with large volumes of water.

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Dr. Brian Staiger is a licensed pharmacist in New York State and the founder of the Q+A website PharmacistAnswers.com. He graduated from the University At Buffalo with a Doctor of Pharmacy degree in 2010. He has been featured in numerous publications including the Huffington Post as well as a variety of health and pharmacy-related blogs. Please feel free to reach out to him directly if you have any inquiries or want to connect! He's answered thousands of medication and pharmacy-related questions and he's ready to answer yours!

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