But this could encourage drug companies to manufacture drugs for a target audience who fit a specific genetic profile with those who don't missing out, warns a US genetics expert.

William Haseltine, head of Human Genome Sciences in Rockville, Maryland, tells New Scientist magazine, that he fears the creation of "personalised medicine" could mean drug companies targeting people with the "right" genetic make-up for the medicines they want to sell.

Scientists believe genetically tailored medicine could lead to an explosion in drugs to fit people with different genetic profiles, but Dr Haseltine is worried that the profit motive might lead to some people missing out.

"We still want new drugs that treat as many people as possible," he says.

But other experts say drug companies have always recognised that there are many factors which influence how people react to drugs, including age and gender.

Daniel Cohen, a geneticist for the Paris-based genomics company Genset, says: "Pharmaceutical companies dream of a drug that treats everyone, but life is such that this is not possible."

Adverse reactions

Scientists believe they are not far off being able to tailor drugs to a person's genetic make-up.

This would mean time and money would be spared trying out drugs on people who might have an adverse reaction to them because of genetic reasons or on whom the treatments would not work.

In some cases, lives could be saved. Around 200,000 Americans died in 1994 because of reactions to drugs.

Scientists predict an explosion in new drugs

In the 1950s, many patients died as a result of a reaction to the muscle relaxant succinylcholine, used in patients undergoing anaesthetic.

It was found that they had inherited a rogue form of the enzyme which clears the relaxant from the body.

In the UK, it is estimated that doctors waste �100m a year prescribing the drugs which are ineffective, unsuitable or do not work for specific types of patients.

Targeting

Karen Schmidt argues in the New Scientist that drug companies will benefit from pharmacogenomics as well as patients.

Drug companies say that, if they can find who will most benefit from a drug, they can target it more effectively, making it easier to show it is safe and effective.

Several have already started collecting DNA from patients involved in clinical trials for new drugs.

There is already research which suggests genetic reasons why some patients respond better to some drugs than others.

For example, people with a common mutant enzyme called cholesteryl transfer protein do not respond to a cholesterol-reducing drug called pravastatin.

Chips

With the advent of the SNP chip, a tool which helps chart the differences in people's DNA.

Affymetrix, a biotech company in California has developed a chip which identifies 12 different variants of two genes involved in the way the body breaks down around 20% of all commonly prescribed drugs.

These include anti-depressants such as Prozac.

But experts believe drug companies may be reluctant to move too fast in the "personalised medicine" field because of fears about the accuracy of DNA testing.