For most people, especially those under the age of about 75, laxatives are only needed in a short course when some other factor or illness is making them constipated, or to prevent straining when the person has a condition such as a hernia or piles.

Occasionally, there are chronic factors interfering with normal bowel movements, such as damage to the nerves in the spinal cord, hypothyroidism, or the use of medicines that can cause constipation (including painkillers and some antidepressants). For these people, long-term use of laxatives may help.

Older people, especially if they're frail or have many chronic diseases, may also be prone to constipation and often need regular medication such as laxatives to help keep the bowels moving.

When laxatives are needed, it's important to choose the right type.

Different laxatives work in different ways

There are many types available, and the main ones are:

• Bulk-forming laxatives: these work like tiny spongy particles that soak up fluid to draw it to the bowel, helping to form a bulky stool that's soft enough to pass without effort. These laxatives are generally considered the safest, but can stimulate gas and bloating in the intestines. Common types include natural fibres such as bran, ispaghula husk, methylcellulose and sterculia.
• Osmotic laxatives: these inert substances pass through the gut without being absorbed into the body, but at the same time increase the amount of fluid in the gut, either by pulling fluid into the intestines from the body or by retaining fluid that has been swallowed with food. As a result, the faeces remains softer. Osmotic laxatives include lactulose (a semi-synthetic sugar), sorbitol (found in large amounts in prunes, which explains their frequent use as a laxative) and macrogols such as polyethylene glycol. Once again, flatulence can be a side-effect.
• Irritant laxatives (stimulant laxatives): These chemical laxatives irritate the bowel lining, which stimulates muscle movement along the length of the intestine, hurrying a stool along. Stimulant laxatives include bisacodyl, senna and docusate sodium (which also acts as a softening agent).
• Lubricant and softening laxatives: Lubricants grease or oil the stool, enabling it to move through the intestine more easily. Stool softeners provide the stool with moisture, preventing it from becoming dry and hard. One of the main types, docusate sodium, is basically a detergent that is not absorbed by the body, but which traps dietary fat and then mixes it with the stool, making hard stools much softer.

Risks of laxatives

One of the biggest problems of long-term laxative use is that the body can grow used to their effects, and normal bowel action may become dependent on the laxative. If the laxatives are stopped, the normal mechanism and activity of the bowel takes a long time to be restored.

Another risk is that, if used in excess, some laxatives can cause diarrhoea and may disrupt levels of salt in the body, which can be dangerous in extreme cases.

Risks of suddenly stopping their use

You may find it difficult to suddenly stop taking laxatives, and could run the risk of becoming very constipated. But you should at least change from senna to a more gentle or natural laxative. Most doctors these days regard senna as a very old-fashioned approach to managing constipation and prefer other methods (although senna, combined with other treatments, may be useful in older people where the muscular activity of the intestines may be very sluggish).

Stop your laxatives slowly and replace their action by other means.

Add bulk to your diet

Increase the amount of natural bulk in your diet, which acts as a bulk-forming laxative. Bulk, which usually comes from plant fibre, isn't absorbed by the gut, but soaks up water as it passes through the intestines. As it swells, it adds soft volume to the faeces, which helps to send signals to the bowel to empty.

In particular, you need insoluble fibre, and you can get this from:

• Wheat bran (sprinkle on to meals or look for cereals that contain it)
• Unpeeled fruit
• Leafy green vegetables
• Wholemeal bread

Also, make sure you're drinking plenty of water - at least three pints a day.

Try other types of laxative

If diet alone isn't enough, ask your doctor or pharmacist for advice on which other laxatives might suit you.

This article was last medically reviewed by Dr Trisha Macnair in April 2008