42.8% for adults (Grucza et al., 2007) and 47.4% for 12th graders (Johnston et al., 2009) in the U.S. DSM-IV cannabis dependence criteria are met by 10 to 18% of cannabis users (Anthony et al., 1994; Hall and Pacula, 2003; Teesson et al., 2006) and in a recent study of adolescent cannabis users, over one third had at least one dependence symptom (Nocon et al., 2006). Like alcohol, severity of symptomatology increases steadily with heaviness of use (Coffey et al., 2002; Nocon et al., 2006). For example, in an Australian sample of young adults, 13% of those who used cannabis once or twice per week met cannabis dependence criteria, compared with 53% of those who used cannabis three or more times per week (Coffey et al., 2002).
