Last week, Europe's first commercial testing service to detect whether a person has been taking drugs by analysing hair opened in Britain.
Unlike urine samples, which detect substances taken in the last 48 hours, hair can reveal whether someone has been taking drugs in the past weeks and even months. It can also distinguish different types of narcotics and when they were taken.
Hair is made from cells which divide and mix with blood at the base of each follicle. Any drugs that are in the blood supply are trapped in the centre of the strand.
Scientists dissolve the hair samples and analyse them for traces of the drug's breakdown products. On average hair will grow at about 1cm a month, providing a personal drugs diary.
The technique has been available in the United States for several years, where it has been used to monitor and treat addicts on drug rehabilitation programmes.
It is also used by companies to detect drug abuse in employees or prospective employees. Some British firms have also used this method to vet their staff.
Supporters of the technique say it is much harder to evade - drug-abusers have been known to give old urine samples from bottles hidden on their body - is more accurate than urine samples, and is easy to collect.
The disadvantages are that some of the drugs can be washed out of hair with regular shampooing and about 15 per cent of a person's hair will stop growing at any one time, giving an old reading.
Future applications are expected to include tests in sport. The new clinic, Tricho-Tech, based at the Cardiff Medicentre, plans to offer analysis for a wide range of drugs, including cocaine, ecstasy and barbiturates. The technique was developed in the United States in the 1980s.