Drugs used to treat constipation are called laxatives. They are often misused – the result of the mistaken belief that there is some relationship between regular daily emptying of the bowels and health. It does not matter if you have your bowels opened two or three times a day or two to three times a week. It only matters if you develop a change in bowel habit; if you only go a day or two over the normal for you, this again does not matter.

We usually talk about laxatives when we wish to produce a soft, formed, easy-to-pass motion and a cathartic or purgative when we wish to produce a fairly quick and fluid emptying of the bowel. Most laxatives are harmless when taken infrequently, but their continued use over long periods of time may lead to complications such as fluid and salt loss. This may make you feel tired, weak and thirsty. Calcium loss may occur and lead to bone softening.

The taking of laxatives is only occasionally necessary; for example, after childbirth, after an operation for piles or some other condition around the anus, after some abdominal operations, after a coronary thrombosis and in elderly or debilitated bedridden patients. Otherwise, the use of a laxative is seldom indicated and you certainly will be no healthier if you drink a glass of health salts every morning.

The most natural treatment for simple constipation is a high fibre diet. This is easily achieved by eating more fruit and leafy vegetables, and wholegrain cereals, and, if necessary, by adding bran to your diet in the form of wholegrain cereal foods. In addition to diet make sure that you drink plenty of fluids, take regular exercise and develop a habit of trying to empty your bowels just after a meal when food entering the stomach stimulates the large bowel to empty its contents into the rectum, which produces the urge to go. Never neglect a feeling that you want to empty your bowels. The same advice applies if you have developed a laxative habit, but, in addition, try to reduce the dose slowly over a period of time.

Laxatives should never be taken to relieve abdominal pains, cramps, colic, nausea or any other symptom, whether associated with constipation or not. If in doubt you should always consult your doctor, particularly if you pass blood in the motions, and/or if you develop a change in bowel habits.

The occasional use of laxatives is not harmful but the danger is that you will develop the laxative habit – when you have taken one dose of laxative and it may take several days before you get the urge to go again. Unfortunately, some people cannot wait that long before taking another dose. A regular routine develops and the bowel action becomes so abnormal that it is then unable to function properly and the person will be totally reliant upon the use of these drugs. These warnings refer to all laxatives which include the old practice of taking health salts before breakfast and numerous patent health remedies.

There are four main groups of drugs used to treat constipation: stimulant, osmotic, faecal softeners and bulk-forming.

1. Stimulant Laxatives

These increase large bowel movements by irritating the lining and/or stimulating the bowel muscles to contract. They may cause cramps, increased mucus secretion and excessive fluid loss. Response to dosage varies tremendously and what may produce stomach cramps and diarrhoea in one person may have no effect in another.

Stimulant laxatives include bisacodyl (Dulcolax), cascara (in Rhuaka), castor oil, dantron (in co-danthramer (Ailax, Codalax, Danlax), in co-danthrusate (Capsuvac, Normax)), docusate sodium (Dioctyl, Docusol), senna (in Boots Compound Laxative Syrup of Figs, Boots Senna tablets, in Califig, Ex-lax Senna, in Fam-lax Senna, in Manevac, in Nylax with Senna, in Potter’s Cleansing Herb, in Rhuaka, Senokot), sodium picosulfate (Laxoberal, in Picolax).

Senna, cascara and dantron may colour the urine red, cause excessive loss of fluids and potassium and if taken regularly may cause patchy pigmentation of part of the bowel (colon). This is not serious and is reversible on stopping the drug. Long-term high-dose administration of danthron is associated with the development of cancer in the intestine and liver of rodents. There is no evidence that danthron produces cancer in humans. It is present with polaxamer 188 in co-danthramer (Ailax, Codalax, Danlax) and with docusate sodium in co-danthrusate (Capsuvac, Ducolax, Normax).

Phenolphthalein may cause allergic skin rashes and colour the urine pink. It should not be used. Bisacodyl (Dulcolax) is related to phenolphthalein. It may be used as a suppository as well as taken by mouth.

Castor oil differs from the other stimulant laxatives because it works on the small bowel and therefore produces an effect in about three hours. Other laxatives act on the large bowel and work in 6–12 hours.

Stimulant laxatives can be given by mouth or rectum. They should only be used to prepare the bowel for surgery or instrumentation or in severe constipation provided there is no evidence of obstruction. They should not be used in children or in pregnancy. Onset of action by mouth takes 6 – 12 hours. Senna is the least powerful , and sodium picosulfate is the most powerful.

2. Osmotic Laxatives (Saline Laxatives)

These are salts of magnesium, sodium or potassium in various mixtures. By mouth or by rectum they are incompletely absorbed and increase the bulk of the bowel contents by drawing liquid into the bowel (a process called osmosis). Some of them are made fizzy by adding sodium bicarbonate and fruity by adding weak acids such as citric and tartaric. These salts may take fluids from the body and cause dehydration, and should therefore be taken with large drinks of water. They include magnesium sulphate (Epsom salts, Andrews Liver Salts), magnesium hydroxide (Milk of Magnesia, in Milpar), sodium sulphate (Glauber’s salts), sodium potassium tartrate (Rochelle salts) and potassium bitartrate (cream of tartar). Eno contains sodium bicarbonate plus citric and tartaric acid. Some of these preparations are called health salts, which is reasonable enough if health is defined as bowel movements and belching.

Osmotic laxatives containing sodium salts should never be given to patients with heart, liver or kidney failure. Likewise they should not be taken by patients on diuretic drugs since these drugs are given to get rid of salt from the body. Magnesium salts should not be given to patients with impaired kidney function; about 20 per cent of magnesium may be absorbed from the intestine and as it is excreted by the kidneys any impairment may lead to an accumulation of magnesium in the blood, resulting in magnesium intoxication.

Lactulose (Duphalac, Lactugal, Osmolax, Regulose) and Lactitol are non-absorbable synthetic disaccharide sugars. They have an osmotic action and increase the fluid bulk of the motions and lead to stimulation of bowel movements. They also affect the acidity and increase the bacterial content of the bowel. They may cause nausea, diarrhoea and wind.

Polyethylene glycol by mouth (in Klean-Prep, in Movical) acts rapidly and clears the bowel prior to X-ray or endoscopy. It may also be used to treat chronic constipation and to treat faecal impaction. Total evacuation of the bowel is achieved within about four hours.

3. Faecal Softeners (Lubricant Laxatives)

There are two types of faecal softeners: mineral oils (e.g. liquid paraffin) and wetting agents such as docusate sodium in co-danthrusate (Dioctyl, Norgalax, Normax) and poloxamer 188 in co-danthramer (Ailax, Codalax).

Liquid paraffin (in Milpar) softens and lubricates the motions. Its regular use should be avoided since it interferes with the absorption of carotene (pre-formed vitamin A), vitamin A and vitamin D. In pregnancy it may reduce the absorption of vitamin K and produce a disorder of blood clotting. Young, elderly and debilitated patients may rarely inhale a few drops into their lungs when they swallow liquid paraffin and this may cause a type of pneumonia. It may also be absorbed from the gut and cause swelling of lymph glands in the gut wall, the liver and spleen. It may also leak from the anus in the night and cause irritation (pruritus ani). It should not be used in children under 3 years of age. It should only be used occasionally to temporarily relieve constipation.

Docusate sodium lowers surface tension and is used in the pharmaceutical industry as an emulsifying or wetting agent. It softens the motions in 24–48 hours. It is also used to soften wax in the ears. Poloxamer 188 is another surface active agent which acts as a lubricant laxative.

4. Bulk-forming Laxatives

These are substances which increase the bulk of the stools by absorbing water which stimulates the bowel muscles to become active. In addition they soften the stools. They usually take 12–24 hours to work. Some bulk-forming laxatives are naturally occurring substances such as gums, e.g. agar, tragacanth; ispaghula husks (Fybogel, Isogel, Konsyl in Manevac, Regulan) and sterculia (Normacol, in Normacol Plus) – these are present in numerous proprietary laxatives. Others are semi-synthetic, like methylcellulose (Celevac). They must be taken with plenty of fluids because of the risk of bowel obstruction in elderly or debilitated patients. Gums may cause hypersensitivity resulting in skin rashes and hayfever/asthma-like symptoms. Bran (Trifyba) is a by-product of the milling of wheat and contains about 20 per cent of indigestible cellulose. It is an effective bulk laxative and may also help to prevent certain bowel disorders such as diverticulitis.

Which Laxative to Take

For occasional attacks of constipation when living habits change (e.g. going on holiday), try a bulk-forming laxative – e.g. bran – and drink plenty of fluids, particularly if the climate is hot. Use a stimulant laxative (e.g. senna) only if necessary. A faecal softener (e.g. docusate sodium) may help after surgery on the anus or if you have painful piles. In pregnancy, change to a high fibre diet and drink plenty of fluids. After childbirth, try a high fibre diet and plenty of fluids. It may occasionally be necessary to use a stimulant laxative

(e.g. senna) or a faecal softener (e.g. docusate sodium). Bulk-forming laxatives (e.g. bran) are useful for treating irritable bowel syndrome and chronic diarrhoeal disorders such as ulcerative colitis. They are also useful in people with colostomies or ileostomies. Terminally ill patients, who may be taking constipating narcotic pain-relievers, may need the regular use of a mixture of laxatives, e.g. a faecal softener (co-danthramer) and/or lactulose with senna.

Bran

Bran comes from the outer layers of wheat grain and its fibre content varies from 30 to 50 per cent depending on the milling process and on the variety of wheat. It is present in such foods as wholemeal bread and certain breakfast cereals. It is useful for treating constipation, and for treating diverticulosis, and it may help patients suffering from irritable bowel syndrome. It is also of use in treating constipation associated with haemorrhoids, anal fissure and ulcerative colitis affecting the lower end of the colon. There are numerous products available to which bran has been added, for instance special breads, biscuits and cereals, or you can buy ‘pure’ bran to add to cereals, etc. The choice is not critical, but everyone should switch from white bread to wholemeal bread and high fibre cereals and reduce or try to stop eating sugary foods and foods made from refined flour. You must drink plenty of fluids to avoid obstruction from bran.

Rectally Administered Laxatives

When the faeces are impacted, laxatives administered rectally may be useful. (Remember in the elderly, impacted faeces due to constipation may present as diarrhoea, a watery leakage of faeces around the impaction.) Preparations available include bisacodyl suppositories (Dulcolax), phosphate enemas (Fleet, Fletchers’) and suppositories (e.g. Carbalax), docusate sodium (Fletchers’ Enemette, Norgolax Micro-enemas), arachis oil (Fletchers’), faecal softener/lubricant enemas: Micolette (sodium lauryl sulpoacetate and glycerol), Micralax (sodium citrate and sodium alkylsulphoacetate) and Relaxit (sodium lauryl sulphate and glycerol), and glycerol suppositories.