For $75 (Pounds 50), hair taken from a brush can be tested for evidence of cocaine, marijuana and other drugs.
"The stakes are getting higher and higher" as drugs increase in potency, said Raymond Kubacki, president of Psychemedics Corp, which introduced the PDT-90 process on July 12. The company's stock price has since tripled.
Surveys by the University of Michigan Institute for Social Research show that half of all 18-year-olds, 40 per cent of 16-year-olds and a third of 14-year- olds have used illicit drugs.
But Loren Siegel, director of public education for the American Civil Liberties Union, says drug use among teenagers is lower than it was in the 1970s and "there is no call for panic".