Man has been troubled by constipation for more than 7,000 years ever since the switchover from feeding on fruits, roots, vegetables and grains to a wide variety of meat products happened. Constipation is of even greater concern world over today due to the shedding of traditional diets what with the convenience granted by fast foods in today’s fast-paced lifestyle. It is also a side effect of drugs such as anticholenergics, anti-psychotics, anti-depressants, antispasmodics and opiates to name a few. The huge trade in purgative drugs, such as aloes, since a long time in history in the west indicates their extensive usage reflecting widespread prevalence of constipation in these societies.

Ayurvedic and Chinese physicians have used many purgative plant drugs including senna and ispaghula to treat various conditions recognized to be linked to constipation. Senna appears to have been used since 9th or 10th century, introduced into medicine by Arabian physicians. Ispaghula is a well-known drug in the Unani system of medicine.

Unlike fibre-rich plant foods such as whole grains that act as bulk laxatives, plants rich in anthraquinone derivatives such as senna, aloes, cascara and rhubarb are stimulant laxatives. The anthraquinone glycosides in the purgative drugs are hydrolysed by the colonic bacteria into active compounds and thus the cathartic action occurs primarily in the colon 8–12 hours after drug administration.

Senna is thus a stimulant laxative acting on the walls of the large intestine, increasing peristaltic movements. After oral administration, the sennosides are transformed by intestinal flora into rhein anthrone which appears to be the ultimate purgative principle. The glycoside residues in the active constituents are necessary for water solubility and subsequent transportation to the site of action. Most of the sennosides are excreted in the faeces as polymers, together with unchanged sennosides, sennidins and rhein anthrone.

Senna is the most widely prescribed laxative, being suitable for both habitual constipation and occasional use. It lacks the astringent after-effect of rhubarb. Despite the availability of a number of synthetics, sennoside preparations remain among the most important pharmaceutical laxatives. Senna products containing total sennosides ranging from 15% to 60% calculated as sennoside B are commercially available.

The laxative action of ispaghula mucilage is purely mechanical and ispaghula seeds are used as an excellent demulcent and bulk laxative in chronic constipation. It is used in irritative conditions of the gastrointestinal tract. The mucilage is not acted upon by digestive enzymes and passes though the small intestine unchanged. It relieves constipation by stimulating intestinal peristalsis by mechanical action.

Though cascara has a similar pharmacological action as senna, in view of its stronger action, its routine usage is not recommended. Aloes and rhubarb on account of their drastic action are largely abandoned from use as purgatives.