As discussed in the epidemiology section, about a third of those adolescents who try cannabis will use it regularly for some period of time, whereas only about 10% will go on to develop long-term dependence lasting into adulthood (Hall and Solowij, 1998). Even among these persistent users, the majority will stop use by age 30 years. Thus, it is possible to extrapolate from these figures that less than 2% of adults will exhibit cannabis dependence during their twenties and probably less than 1% of adults will continue use into their thirties, suggesting a good prognosis for the major-ity of cannabis-dependent patients under age 30 years. However, for the small minority who continue to suffer from cannabis de-pendence into their thirties, most follow a chronic or relapsing course similar to those who suffer from dependence on other substances (Miller et al., 1989; Hall and Solowij, 1998; Johnston et al., 2001; Zoccollilo et al., 1999; Anthony et al., 1994; Chen and Kandel, 1995, 1998; Chen et al., 1997; Kandel and Chen, 2000, Stephens et al., 1993a, 1993b, 1994, 2000; Baer et al., 1998; Hser et al. 2001; Hubbard et al., 1985).
Cannabis abuse and dependence appear to pursue a be-nign course in many individuals; many studies have suggested that individuals suffering from these disorders do not differ in ability to function in society from matched control subjects who are not users (Kouri et al., 1995; Simon et al., 1974; Pope et al., 1990, 2001b; Zinberg and Weil, 1970; Comitas, 1976; Hochman and Brill, 1973; Boulougouris et al., 1976; Robins et al., 1970; Mendelson et al., 1976; Brill and Christie, 1974; Pope and Yurgelun-Todd, 1996). However, a few studies have described an “amotivational syndrome” associated with chronic cannabis use, characterized by subjective reports of lack of direction, motiva-tion and ambition (Mellinger et al., 1976; Lessin and Thomas, 1976; Kupfer et al., 1973; Burdsal et al., 1973; Campbell, 1976; Hendin and Haas, 1985; Musty and Kaback, 1995; Gruber et al., in press). This “amotivational syndrome” appears to result from the effects of continuous intoxication and resolves when cannabis is discontinued (Johns, 2001). In the context of a recent study involving 108 chronic, long-term cannabis users (Pope et al., 2001a; Gruber et al., in press), the authors encountered a number of chronic long-term cannabis users who reported lack of direc-tion, motivation and ambition while using cannabis heavily, but then reported increased productivity and success in their work and social lives after discontinuing use.
Cannabis intoxication is a self-limiting state that remits as can-nabis is metabolized and eliminated from the body. If symptoms suggestive of cannabis intoxication persist, other diagnoses should be considered. Similarly, although there are few data re-garding the course of the other cannabis-induced disorders, it ap-pears that cannabis-induced psychotic and anxiety disorders, as well as cannabis intoxication delirium, rarely persist beyond the period of acute intoxication with the drug. For example, although there have been reports of cannabis-induced psychoses persisting for days or even weeks beyond the time of acute intoxication, a review of the literature (as discussed earlier) was unable to ex-hibit a series of unequivocal cases in which such symptoms per-sisted in the absence of an underlying Axis I disorder. Therefore, symptoms of delirium, psychosis, or anxiety persisting more than 24 to 48 hours after acute cannabis intoxication suggest that another Axis I disorder, rather than cannabis itself, is responsible for the symptoms (Gruber and Pope, 1994; Hall and Degenhardt, 2000; Johns, 2001).