Different Type of Osmotic Laxatives

Different Type of Osmotic Laxatives

Hyperosmotic laxatives are used to treat constipation and cleanse bowel prior colonoscopy or colon surgery and to treat certain types of poisoning. They are substances that contain active ingredients causing colons to hold more water within through osmotic effect. This effect produces softer and easier-to-pass-through stools and stimulates muscles of the walls of colons to contract and squeeze the feces along.

Forms of Osmotic Laxatives

They are available in oral or suppository form, some can be bought over the counter while others require a prescription. Oral form laxatives took 12 hours to 3 days to take effect while rectal form take effect within an hour. Some of the common types includes Miralax (polyethylene glycol PEG), Lactulose, Milk of Magnesia, sorbitol and [easyazon_link identifier=”B00EILMM3A” locale=”US” tag=”wlaxative-20″]glycerin suppositories[/easyazon_link].

Generally, there are 3 types of oral osmotic laxatives which are saline, lactulose and polymer types.


Brand Examples

Time to Effect

Usage Guide



Phillips Milk of Magnesia®

30 min to 6 hours

short term occasional constipation

kidney disease



1-3 days

short term occasional constipation

kidney disease



1-2 days

constipation including long term chronic type

diabetes, lactose intolerant

Milk of Magnesia – Salts or Saline type

Magnesium hydroxide, or often called as “milk of magnesia” because of its milk-like appearance, is an inorganic compound mostly chemically produced from sea water or brine. It is saline type laxative available over the counter to relieve occasional constipation rapidly through increasing water content in intestines. It is not for long term repeat consumption and people with kidney or heart disease should avoid taking this.

Lactulose – Sugar-Like type

Lactulose is a form of sugar that cannot be absorbed by digestive system. It is used for long term chronic constipation treatment. It retains water in the colon, lowering PH through bacterial fermentation and increase the speed of intestinal contractions. It produces result slower (about 48 hours) before bowel movement to happen. It is available over the counter but should be used with care, especially those with diabetes, lactose intolerant, pregnant women and breastfeeding mothers. Examples of osmotic laxatives of this type includes Cephulac, Cholac, Chronulac, Constilac, Constulose, Duphalac, Enulose, Generlac and Kristalose.

Miralax – Polymer type

[easyazon_link identifier=”B00KAOTACA” locale=”US” tag=”wlaxative-20″]Miralax[/easyazon_link] is one of the popular brand name of osmotic laxatives that uses polyethylene glycol (PEG) to treat occasional constipation for short team. It can be bought over the counter without prescription. Based on user review scoring in few medical sites, it ranks very well in term of effectiveness in treating constipation by many user reviews. It was known to cause less bloating, cramping and gas.


People with diabetes and lactose intolerant should avoid lactulose type laxative while those with impaired kidney function should avoid saline type laxatives that contain magnesium or phosphate salts. Laxatives containing sodium should be avoided for individual with congestive heart failure, kidney disease, and high blood pressure.

Side Effects

Side effects of osmotic laxatives vary depends on the type of products used. For example, saline laxative may cause severe dehydration and electrolyte depletion from water loss.

In general, osmotic laxatives are effective and safer as compared to stimulant laxatives to treat acute and short term constipation. Small oral doses should be taken with at least 8 ounce glasses of water to lower common side effects like nausea, abdominal cramping, or gas. Larger doses can be taken to bowel preparation prior colonoscopy, sigmoidoscopy, and barium enema.