Persistent cannabis use is associated with significant morbidity. Persistent use poses health problems similar to those of tobacco (Taylor et al. 2000; Mittleman et al. 2001; Fisher et al. 2005; Hashibe et al. 2005; Tashkin 2005), is implicated in syndrome characterized by apathy, loss of goal-directed behavior, and cognitive impairment termed the “amotivational syndrome” (Sharma 1975; Pope et al. 2001; Solowij et al. 2002; Schuckit 2006), and is associated with impaired educational and work performance (Kandel & Chen 2000; Lynskey & Hall 2000; Swift et al. 2001; Schuckit 2006). Cannabis use, particularly by adolescents and young adults, may also facilitate progression to other illicit drug use (the “gateway” drug hypothesis) (Fergusson & Horwood 2000; Lynskey et al. 2003). In the general U.S. population, cannabis dependence is significantly co-morbid, not only with alcohol and other drug dependence, but also with anxiety, depression, and personality disorders (Regier et al. 1990; Troisi et al. 1998; Agosti et al. 2002; Conway et al. 2006; Stinson et al. 2006) suggesting that cannabis dependence shares etiological relationships with other substance use and psychiatric disorders.
