Cannabis is the most commonly used illicit substance among adolescents and young adults in the United States.7 In 2004, 46% of high-school seniors reported having tried cannabis at some time, 34% reported having used within the past month, and 5.6% reported having smoked cannabis daily.8 Initiation into cannabis use typically begins in adolescence, as youths aged 12 to 17 years constitute about two-thirds of the new cannabis users.9 Approximately 14% of adolescent-onset cannabis users develop cannabis dependence, a rate roughly twice that reported for adult-onset users.10 Further work has focused on the biologic mechanisms involved in the development of cannabis dependence, and this has elucidated some of the underlying pathways from cannabis use to behavior and the potential for the development of problems. For example, the receptor for cannabinoids (CB1) belongs to the Gi/Go protein-coupled receptor family, and, in the mammalian brain, is densely diffused in regions involved in the processing of emotional inputs, rewarding stimuli, habit formation, and higher cognitive functions.11
