Osmotic Laxatives for Constipation

Can OTC Laxatives Help You Find Relief?

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Osmotic laxatives are used to treat constipation. The products that are classified as osmotic laxatives vary. In general, they all work by increasing the amount of water that is secreted within the intestines. This effect helps to produce softer, easier-to-pass stools.

Some osmotic laxatives are available over the counter while others require a prescription. Let's take a look at the three most common types of osmotic laxative brands that you might try to find relief.


Miralax (polyethylene glycol PEG) is a medication that draws water into the stool. This results in a softer stool and induces more frequent bowel movements. There is no need for a prescription, Miralax is available over the counter.

There is one published report that Miralax was more effective than Zelnorm in increasing the number of bowel movements and improving symptoms in patients who suffer from chronic constipation. Miralax seems to cause fewer gastrointestinal side effects (such as bloating and flatulence) than the other osmotic laxatives.


Lactulose is not absorbed by the digestive system and this makes it available to be metabolized by microbes in the intestines. This fermentation process produces fatty acids that pull water into the colon and increase the speed of intestinal contractions.

Lactulose is sold under a variety of brand names. These include Cephulac, Cholac, Chronulac, Constilac, Constulose, Duphalac, Enulose, Generlac, and Kristalose.

Milk of Magnesia

Considered a saline laxative, Milk of Magnesia is available over the counter. This product is rarely recommended by physicians today because safer and more effective alternatives exist.

Milk of Magnesia should be avoided by anyone who suffers from heart or kidney disease.

The Side Effects of Osmotic Laxatives

Side effects of osmotic laxatives vary by the type of product used. In general, the side effects of osmotic laxatives are fairly minimal. When side effects are present, the symptoms may include nausea, bloating, cramping, flatulence, and diarrhea.

In rare cases, some of the side effects of osmotic laxatives can be severe and life-threatening. These are most often experienced by people who overuse the products or who have serious, underlying health issues. Dehydration and an electrolyte imbalance are the two most worrisome of these side effects.

To avoid any of these side effects, use a laxative only when needed and try to limit their long-term use. While this strategy is a good way to prevent unwanted effects on your health, it will also keep your bowel movements in balance. There's really no point in overdoing it on a laxative to relieve constipation only to have your body switch over to a period of diarrhea.

Do These Laxatives Actually Work?

The most recent review of quality research on osmotic laxatives conducted by The American College of Gastroenterology (ACG) finds good support for the effectiveness of Lactulose and Miralax. It says that these two play a role in "improving stool frequency and consistency" in patients who suffer from chronic constipation.

A previous review concluded that there was no substantial evidence for the effectiveness of Milk of Magnesia.

A Note From Verywell

Osmotic laxatives, particularly Lactulose and Miralax, appear to be safe, effective options for easing constipation. If you are considering the use of an osmotic laxative, discuss this with your physician and be sure to follow dosing instructions carefully.

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