September 15, 2011

A laxative is a medicine that loosens the bowel contents and encourages evacuation. A laxative with a mild or gentle effect on the bowel is known as an aperient; and one with a strong effect is known as a cathartic or purgative. Laxatives facilitate evacuation by increasing the stool volume and stimulating the large intestinal muscle by increasing the intestinal pressure. This in turn triggers evacuation.

Signs of constipation are bowel movements that are difficult, painful, or less frequent than normal. Constipation can be prevented by drinking adequate amounts of water about 6-8 glasses per day, getting sufficient fiber by eating fruits, vegetables, and grains, and exercising regularly. Fiber is important because it provides the media for the bacteria to multiply and grow. A good bacterial action results in a larger volume of stool and smooth bowel movement. Laxatives should be used only as the last resort to treat constipation. A physician is best qualified to determine when a laxative is needed and which type is best.

A differential diagnosis should be done before recommending laxatives. A chronic constipation may be one of the symptoms of a serious problem like diverticulitis or when it develops in the later decades as a new complaint may herald colon cancer. Complaints of chronic constipation may also be due to obsessivecompulsive disorder. Laxative should not be used for these conditions. Normal bowel movements are variable, and may vary from two times daily to two to three times weekly. There are many reasons why a doctor may prescribe a laxative to empty the contents of the bowel. A laxative may be prescribed for preparation for a medical examination such as colonoscopy, preparation for a surgery, prevention of constipation secondary to drug therapy, to prevent straining during defecation after a surgery, and as a prophylactic measure for patients recovering from myocardial infarction.

Laxatives are classified according to the mechanism of action. There are five main types of laxatives, but some laxatives act in more than one way. Bulk-forming laxatives increase the volume of the stool. They also soften the stool and stimulate the bowel in a natural way by forming a bulky mass. Psyllium (Metamucil) and methylcellulose (Citrucel) belong to this group. They absorb water and expand as they pass through the digestive tract. Psyllium is one of the rich sources of fiber. Fiber is the indigestible material in plant foods. Psyllium should be taken with adequate amounts of water to avoid choking and obstruction of the esophagus, throat, and intestines.

Stimulant laxatives increase the peristaltic movement of the intestine. Dulcolax, Ex-lax, and Senecot are examples of this type. These agents can be used if bulk-forming laxatives have no effect. Check with your doctor before taking them. They are the most habit forming and should not be taken everyday. Do not take these with milk. They may cause cramps and abdominal pain.

Stool softeners act as detergents, moisturizing and breaking up the feces. Docusate (Colace) belongs to this group. It holds water within the fecal mass, and thus provides a larger, softer stool. Docusate is not recommended for acute constipation. In order to be effective, this should be taken before the fecal mass is formed. This is suitable for recurrent constipation and to prevent constipation caused by certain medication.

Lubricant laxatives include mineral oil, castor oil, and olive oil. They act by reducing intestinal absorption of fecal water and help with easy passing of stool. They are usually taken with other laxatives. Mineral oil is not recommended for long-term use.

Osmotic laxatives are glycerin and lactulose. They prevent the bowel from absorbing water so that the bulk volume increases. Lactulose may also increase peristaltic action of the intestine.


Laxatives should be taken only with the advice of a physician. Chronic use of laxatives may result in a fluid and electrolyte imbalance, steatorrhea, osteomalacia, diarrhea, cathartic colon, and liver disease. Bulk-forming laxatives may delay the absorption of some medications taken at the same time as the laxative. Insulin-dependent diabetics may need to reduce insulin dosage while taking psyllium products. Mineral oil taken regularly leads to deficiency of fat-soluble vitamins. Minerals and docusate should not be taken together because docusate will absorb the mineral oil.

Some people take laxatives to promote weight loss. Laxatives do not promote weight loss. When laxatives are overused, they create dependency and worsen constipation. Laxatives lead to the loss of body fluids, and the body, in turn, compensates for dehydration by retaining water, which results in bloating. Children and pregnant women should not take laxatives without consulting their physician.

SEE ALSO: Constipation, Diet

Suggested Reading

  • Cummings, M. (1991). Overuse hazardous: Laxatives rarely needed. FDA Consumer, 25, 33—35.
  • Friedman, G., Jacobson, E. D., & McCallum, R. W. (Eds.). (1997). Gastrointestinal pharmacology. Philadelphia: Lippincott-Raven.
  • Fuchs, C. S., Giovannucci, E. Colditz, G. A., et al. (1999). Dietary fiber and the risk of colorectal cancer and adenoma in women. New England Journal of Medicine, 40, 169—176.

Lehne, R. A. (2001). Pharmacology for nursing care. Philadelphia: W. B. Saunders.


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