Worldwide, the cumulative incidence of lifetime cannabis use ranges from 0.3% in China to 42% in the United States [1]. Of those who use cannabis in the United States, approximately 40% and 7% develop DSM-IV cannabis abuse and dependence respectively [2], both of which are representative of cannabis use disorders. Cannabis abuse is defined by the endorsement of one of four DSM-IV criteria (recurrent legal problems, hazardous use, use despite social and interpersonal problems and failure to fulfill major role obligations) [3]. A diagnosis of cannabis dependence requires the experience of 3 or more of 6 DSM-IV criteria (tolerance, use in larger quantities or for longer than intended, repeated unsuccessful attempts to quit or cut back, giving up important activities, spending excessive time acquiring or using cannabis and recurrent use despite physical and/or emotional problems; DSM-IV currently does not recognize withdrawal as a dependence criterion for cannabis). Cannabis use disorders commonly represent the experience of these problems or abuse/dependence diagnoses. In 2006, cannabis use disorders contributed to 16% of the admissions to U.S. substance abuse treatment centers – second only to alcohol-related admissions [4].
