Nowadays laxatives are used to treat constipation and to prepare the bowel for medical procedures such as endoscopy. They work in three main ways: by adding bulk to the stools, by softening them, or by stimulating muscular contraction by the bowels. The easiest way of increasing the bulk of the stools is to increase the amount of water they contain; previous generations used to take a daily dose of either Epsom salts (magnesium sulphate) or Glauber's salts (sodium sulphate). Some modern laxatives rely on vegetable fibre such as wheat bran. Like the old- style salts, these retain large amounts of water and so make the stools soft as well as increasing their size. Alternatives to bran include the seaweed preparation agar, psyllium seeds, and methylcellulose. Both prunes and figs act as bulk laxatives.
Liquid paraffin is probably the best known laxative of the softening group, but it has gone out of favour among doctors because prolonged use has been linked with bowel tumours and other complications. Safer softening agents are available, such as dioctyl sodium sulphosuccinate, but these are often combined with stimulants. The stimulant laxatives are the notorious ones. Castor oil has such a powerful effect that it usually empties the bowel completely. All the traditional plant preparations have the disadvantage that their effects are difficult to predict with accuracy, and cascara, aloes, and senna have largely been replaced by the use of synthetic stimulants such as bisacodyl (Dulcolax). Stimulant laxatives may be given as tablets or as suppositories.
Enemas are the ultimate weapon in the medical battle against constipation. Our ancestors suffered torments from enemas based on substances such as turpentine. A few so-called natural healers still administer coffee enemas and other detoxifying mixtures. There is no evidence that any of these are any more effective than water.
Laxatives are old-fashioned remedies for an old-fashioned disease. Constipation is sometimes defined as having fewer bowel actions than the individual thinks is healthy. The action of the bowels is, like sleep, very variable. Some people have a bowel action three times a day, others only twice a week. Attempting to achieve a uniform regularity goes against nature. Furthermore, the current orthodoxy is that we should all be eating a high-fibre diet, with lots of fruit, raw and lightly cooked vegetables, beans and wholemeal bread. This diet, which protects against both heart disease and cancer, will usually also rule out constipation.