The prevalences of substance dependence in the general population are estimated to be around 6-8% for alcohol dependence and 7-14% for marijuana dependence (Kandel et al., 1997a; Young et al., 2002). Substance use and dependence in adolescents confers substantial health risks to the adolescent, including physical problems and psychopathological problems (Kandel et al., 1997b; McGue and Iacono, 2005). Furthermore, drug use and dependence have a significant negative effect on society, given associated crime, reduced workplace productivity, and increased health care costs. These were estimated to cost the United States $143.4 billion in 1998, with a predicted 5.9% increase annually (Office of National Drug Control Policy, 2001). Therefore, adolescent substance dependence is a critical personal and public health concern.
