http://my.webmd.com/content/dmk/dmk_article_1458253
Laxative is any substance that speeds the emptying of the bowels (intestines). Laxatives are often used in the treatment or prevention of constipation (infrequent bowel movements).
Q: What substances are used as laxatives?
A: There are three main groups of laxatives, which differ in the way they affect the intestine. The group most commonly used acts by irritating the bowel wall or by direct nerve (neuronal) stimulation, causing a contraction and expulsion of the feces. Senna and cascara are examples of this type and are found in many commercial preparations.
A second group of laxatives acts by attracting water from the body into the intestine, increasing the volume of feces. Milk of magnesia, Epsom salts (magnesium sulfate), and Glauber's salts (sodium sulfate) are common examples.
The third group, referred to as bulk laxatives, acts as a stimulant to defecation by swelling the contents of the intestine. Bran, vegetable fiber, and general roughage are all bulk laxatives. The diet of many people in Western countries is deficient in these bulk substances; this deficiency may lead to constipation as well as other disorders, such as colorectal cancer.
Q: What are the dangers of using laxatives?
A: Laxatives should not be taken continually over long periods of time because the bowels may become lazy and fail to function on their own. (This is especially true of laxatives that irritate the bowel wall.) Permanent damage to the colon can occur with laxative abuse. Laxatives may also cause side effects in other parts of the body, including chemical and nutritional disturbances.
Q: Should laxatives be used to treat all forms of constipation?
A: No. Laxatives should never be used if constipation suddenly occurs or if it is accompanied by abdominal pain or fever. In such a case, there may be an intestinal obstruction or appendicitis, and laxatives are likely to make the condition worse. A physician should be consulted.