Health: Drug of the century

Most people have a potent anti-cancer agent in the medicine cabinet at home, though few know it. They keep a heart drug at the back of the sock drawer, a fertility promoter buried in their handbag and a cognitive enhancer standing next to the salt pot in the kitchen.

The drug is aspirin, a chemical entity for which new uses are still coming to light 100 years after it was discovered. We know, of course, that it reduces aches and pains, and eases fevers in diseases such as flu. It is now also a standard treatment for heart attacks - take one immediately after calling 999. Tens of thousands of lives could be saved if this simple fact were better known.

It is being tested as a preventive agent against Alzheimer's disease, it has been shown to reduce the risk of stroke, and it can ward off cancer. Those who take it regularly have a 40 per cent reduced risk of dying of cancer of the oesophagus, stomach and bowel. Research also suggests it is effective against herpes and prostate cancer.

Aspirin can fairly claim to be the 20th century's broadest-spectrum medicine - the closest we have come to a miracle drug. Bayer, the German company that discovered it, has earmarked Monday 8 March as the official birthday, though there is some dispute about exactly when the centenary falls. The company plans to wrap a 400-ft tower at its headquarters in Leverkusen, with the help of 50 Alpine mountaineers, to create the world's largest aspirin pack and earn itself a place in the Guinness Book of Records.

Aspirin is derived from the salicin found in willow bark, and records date from 400BC, when Hippocrates recommended willow bark infusions to ease labour pains. Interest was revived in 1753 by the Reverend Edward Stone who was tempted to chew on the bark of the white willow while walking in a field near Chipping Norton. He may have been influenced by an old theory of medicines known as the Doctrine of Signatures. This held that the cure to a disease might be found in the same place as the cause. Fevers were believed to be aggravated by damp, and willows flourished in damp places.

Chewing the bark, Stone noticed that it tasted bitter, like "Jesuits' bark", from a Peruvian tree, which was used as a painkiller and which we now know to contain quinine. He made an infusion of the willow bark and gave it to 50 people suffering from fever. It proved effective and Stone reported his results to the president of the Royal Society.

It was not until 1897 that Felix Hoffman, a German chemist working for Bayer, found a way to reduce the side-effects of salicylic acid, the active ingredient of willow bark, which included severe irritation of mouth, oesophagus and stomach, by combining it with an acetyl group to make aspirin. Despite this advance, the new drug was dismissed by Heinrich Besser, the head of Bayer's Pharmacological Institute, as "typical Berlin hot air". Bayer's chairman intervened, after seeing the result of laboratory tests, and the rest is history.

By 1950 aspirin was the best-selling painkiller and in 1969 it went to the moon with Neil Armstrong aboard Apollo. But its mechanism was still a mystery. In 1966 The New York Times called it "the wonder drug that no one understands".

By then aspirin was being challenged by newer painkillers such as paracetamol and, later, ibuprofen. Paracetamol lacks aspirin's irritant effect on the stomach - severe in 6 per cent of the population - and sales rose rapidly. Both drugs are equally effective at reducing pain and fever but aspirin has an additional anti-inflammatory effect, like ibuprofen, and is better than paracetamol for sprains, cuts and bruises where swelling is involved. However, it should not be taken by children under 12 because of the risk of Reye's syndrome, a rare disorder that can cause delirium, convulsions and death.

Sales of paracetamol overtook those of aspirin in the late Seventies and the newer drug now has 90 per cent of the analgesics market. But aspirin was about to undergo a renaissance that would lift it into a different class. Dr John Vane of the Royal College of Surgeons unlocked the secret of aspirin's mechanism, and opened up a vista of new therapeutic opportunities. Dr Vane, whose work earned him a knighthood and a Nobel prize, discovered that aspirin works by inhibiting production of prostaglandins, hormone- like substances made in almost all the body's cells, which trigger pain signals to the brain. Prostaglandins are involved in many diseases. In heart disease, a prostaglandin-like substance called thromboxane promotes clotting. A single daily aspirin inhibits production of thromboxane, effectively reducing the blood's tendency to form clots, and cuts by a third the incidence of heart attacks in those at risk.

Aspirin's anti-inflammatory properties help the pain of arthritis and it was a chance observation that sufferers who took it had a lower incidence of Alzheimer's disease, which suggested the drug might have a protective effect on the brain. Now a 10-year trial of 400 men is about to start in Cardiff, run by the Medical Research Council, in which half will be given 100mg of aspirin and half a placebo to see whether the drug can stave off Alzheimer's.

Aspirin can reduce the risk of strokes and cuts the incidence of pre- eclampsia, a dangerous condition in pregnancy that can threaten the lives of mother and baby. In women undergoing in-vitro fertilisation who have an immune system problem caused by raised levels of antiphospholipid antibodies, a daily aspirin more than doubles their chance of getting pregnant.

Aspirin today has a slightly dowdy image, partly because it is cheap and has been with us for so long. But it has shown a repeated capacity to surprise over the last 100 years. It is a safe bet that the party is not over for this remarkable drug.