Health: A technique to comb out the drug users: Addicts can lie to conceal their habit; they can even cheat on urine tests - but they cannot rig the evidence hidden in the hair on their heads. Jason Bennetto reports

MAGGIE became a prostitute and crack addict shortly after she moved to London. She had previously been hooked on heroin but left her home in Hampshire when her one-year-old son was made a ward of the court because of her drug habit.

Her decline in the capital was rapid. As she became more desperate for regular fixes of crack cocaine she took more risks. She started robbing punters and was threatened with a knife several times. Repeated attempts at a variety of drug-rehabilitation programmes failed.

That was about two years ago. Maggie, 29, is now living in Cornwall with a new boyfriend and has a job at a fish-and-chip shop. For the past 14 months she has been taking methadone, a chemical substitute for heroin.

The major difference between this drug programme and others is the addition of a test that will show if she has been cheating. The test provides an irrefutable record of her recent drug history - from the analysis of a hair from her head.

Hair grows at about a centimetre a month and drugs leave traces in it. Unlike urine samples, which usually only detect substances taken in the previous 48 hours, a hair can reveal whether someone has been taking drugs in the past weeks or months and even what drugs they have been taking. It is possible to 'read' the hairs centimetre by centimetre and produce a personal drugs diary. About every two months Maggie visits her GP, who takes two strands of hair from her head for analysis. She is convinced that this method of checking up is helping her stay off illegal drugs.

'It's a better system because even if you want to reform yourself people will always doubt you. But this way you have proof you are drug free. Another motivation is that I know if I try and cheat I'll get caught. The main reason, however, is that I want my son back and with this system, no one will be able to argue that I can't be trusted.'

Maggie confirms that drug users know a great deal about cheating when taking urine tests. Some will stop taking their drugs a couple of days before giving a sample, just to appear drug free. 'I used to get a friend to give me a urine sample which I would hide in a bottle in my coat. It's very rare for anyone to actually watch you while you take a pee, so it was easy to substitute it for my own sample,' she said.

Supporters of the hair technique say the fact that it makes cheating almost impossible is a significant point in its favour. In addition, they claim it is more accurate and sensitive than urine samples, and is easy to collect. The technique, developed in the early Eighties by Dr Werner Baumgartner, an American chemist, has even been used to debunk some historical myths. Analysis of a lock of 170-year-old hair from John Keats found evidence of the opium the poet used as a painkiller. A similar test on Lord Byron's hair proved negative, and a sample of Napoleon Bonaparte's hair revealed that he did not die from arsenic poisoning, as was popularly supposed.

Until recently, Maggie's hair was sent to the United States, but in December a new commercial service opened in Britain. Organisers of drug treatment clinics believe the technique will become increasingly popular as a growing number of applications are developed for the technique. Although the hair test can distinguish between different types of narcotics and when they were taken, Tricho-Tech, the Cardiff-based British clinic, currently only tests for heroin and methadone.

When drugs are metabolised in the body they produce breakdown products that diffuse into the hair follicles and are deposited in the growing cells. The hair grows longer as the cells move upward along the hair shaft by the formation of new cells below. A chemical change, called keratinisation, occurs that transforms the cells into the fibrous structure of hair. This process also traps any drug content, which remains sealed in the hair shaft. To find out what a patient has been taking, sections of a hair are analysed, chronologically, for traces of different drug products. The analyst takes one centimetre pieces, each representing about a month's growth, weighs them, dissolves them and calculates which drugs have been taken in that month. A test costs about pounds 40.

Dr Colin Brewer, medical director of the Stapleford Centre, a private drug rehabilitation clinic in London, and honorary medical director of the new testing centre in Cardiff, uses hair analysis for about 300 of his clients. Most tests are to monitor drug users' progress on treatment programmes, but about a quarter are to obtain evidence for defendants

in court cases to show they have been drug free. And several dozen clients use the method to prove to their parents or employers that they have not been taking narcotics.

Dr Brewer believes that the hair test has saved at least one man from a jail sentence. The man, a heroin addict, pleaded guilty to a burglary which he had been carrying out to get money for drugs. In mitigation he argued that since the crime he had sought treatment, and hair analysis was used to show that he had been heroin-free for several months. He was given a probation order, rather than being sent to prison.

Dr Brewer said: 'Urine samples are relatively easy to evade, whereas hair testing is not. Self-reporting is often inaccurate, and because people perceive the technique to be all-seeing, they give up lying and trying to beat the system.'

But there are disadvantages. A small amount of the drug breakdown products can be washed out of hair with regular shampooing. And since about 15 per cent of a person's hair will stop growing at any one time, a sample may not always contain up-to-date information.

There is, as yet, no direct correlation between the amount of drug trace products found in a hair sample and the amount of narcotics a person is taking. But for an individual taking a steady dose - such as prescribed methadone - the hair levels are constant through the hair, which provides accurate monitoring.

Some drug experts have criticised hair analyis for being relatively untested and of limited use. Critics are concerned that rogue results might be caused by external contamination or 'leaching' from the hair. The test also raises civil liberty questions regarding rights to information about a person's drug history.

The number of companies that carry out drug tests on their employees or prospective employees is increasing. So far only a few British firms have used this method to vet their staff, but it is much more popular in the United States, where it has been available for several years.

Dr John Strang, Getty senior lecturer in addictions at the National Addiction Centre in London, which carries out hair tests for clinical and research work, is cautious about future applications.

'There are some huge moral and ethical issues, especially with employment screening - what is public and what is private information?' he said. 'The technology is there, but further work needs to be done to check how accurate it is over a long period of time. Initial evidence suggests it is pretty reliable.'

Tricho-Tech plans to offer analysis for a wide range of drugs, including cocaine, ecstasy and barbiturates. Hair analysis could also be used in sport to expose those atheletes who avoid detection simply by not taking their drugs several weeks before competing.