The number of drug users documented officially by Chinese public security departments increased from 70,000 in 1990 to 1.14 million by 2004 [9] while the estimated number is 3.5 million [1] . The lifetime prevalence rates of illicit drug use among residents age 15 years or older in high-prevalence Chinese cities increased from 1.1% in 1993 to 1.6% in 1996, and the 1-year prevalence rate increased from 0.9% to 1.2% during this period [10, 11] .