What Are Osmotic Laxatives and How Do They Work?

glass of water on a pink and blue background

Even when you exercise, drink plenty of water and eat high-fiber foods, you can sometimes feel blocked and may experience occasional constipation. The use of an osmotic laxative like MiraLAX® can help relieve occasional constipation.


You may notice that the word “osmotic” is pretty close to “osmosis,” which means we’re talking about the movement of water. Osmotic laxatives, such as MiraLAX®, attract water and keep it in your colon. This action allows MiraLAX® to hydrate and soften stools, and unblock your system without causing harsh gastrointestinal side effects.


Basically, osmotic agents, such as polyethylene glycol found in MiraLAX®, work naturally with the water in the colon to unblock a person’s system. Soluble, non-absorbable PEG 3350 hydrates, softens and eases stools by gently attracting water in the colon through a process known as osmosis. The water increases stool volume and stretches the wall of the bowel, triggering the defecation reflex so the digestive system can be unblocked naturally.


It all depends on what kind of osmotic laxative you have. Some of the products that fall under this category are pre-mixed liquids, some are tablets you chew up and swallow, and some are powders, e.g., MiraLAX®, which you mix into 4-8 ounces of a liquid before drinking. MiraLAX® can be mixed into any beverage, hot or cold. Some examples include coffee, tea, water, orange juice, iced coffee, ice water, coconut water, smoothie, iced tea and seltzer.


Osmotic laxatives, such as MiraLAX®, are generally well-tolerated and have very few side effects. Studies have shown that MiraLAX® increases bowel movement frequency with less straining and improves stool consistency. If gastrointestinal side effects do occur, they are usually mild and transient.


Jin J. JAMA. 2014;312:1167. Leung L et al. JAFBM. 2011;24:436-451; QuintilesIMS Survey 2018, Pharmacy Times Survey 2018, QuintilesIMS Survey 2018. Accessed September 14, 2017. DiPalma JA et al. South Med J. 2007;100:1085-1090. Cleveland MV et al. South Med J. 2001;94:478-481. DiPalma JA et al. Online J Dig Health. 1999;1:1-10.


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