Mental health differences between frequent cannabis users with and without dependence and the general population.

AIMS To compare the prevalence of mental disorders between frequent cannabis users with and without dependence and the general population. DESIGN Cross-sectional comparison of interview data. SETTING Enriched community sample of frequent cannabis users and a representative sample of non-users and non-frequent users from the general population. PARTICIPANTS A total of 521 young adult (aged 18-30 years) frequent cannabis users, 252 of whom were with DSM-IV cannabis dependence (D+) and 269 without DSM-IV cannabis dependence (D-), and 1072 young adults from the general population. MEASUREMENTS Multinomial logistic regression was used to compare groups regarding the presence of DSM-IV mental disorders. Detailed measures of cannabis use, childhood adversity and other substance use were considered confounders. FINDINGS Compared with the general population, externalizing disorders were more prevalent in D- [odds ratio (OR) = 8.91, P < 0.001] and most prevalent in D+ (OR = 17.75, P < 0.001), but internalizing disorders were associated only with D+ (mood OR = 4.15, P < 0.001; anxiety OR = 2.20, P = 0.002). Associations were attenuated (and often became non-significant) after correction for childhood adversity and substance use other than cannabis. However, the prevalence of mental disorders remained higher in D+ compared with D- (OR = 2.40, P < 0.001), although cannabis use patterns were remarkably similar. CONCLUSIONS Cannabis use patterns, childhood adversity and the use of other substances are similar in dependent and non-dependent frequent cannabis users. With the exception of more externalizing disorders, the mental health condition of non-dependent frequent cannabis users is similar to that of the general population, whereas it is worse in dependent frequent cannabis users.