Adult Mental Health Consequences of Marijuana Use in Adolescence and Young Adulthood

Introduction: Moderate marijuana use among adolescents and young adults is relatively common. However, heavy or regular use has been associated with negative long-term consequences. The present study is a prospective, longitudinal examination of the relationship between persistent regular marijuana use from adolescence through young adulthood and mental health outcomes at age 33.

Methods: Data were drawn from The Seattle Social Development Project. Mental health outcomes were assessed at age 33 (2008) and included both DSM-IV diagnosis (1=yes, 0=no) and symptom count for (1) generalized anxiety disorder; (2) major depression; (3) social phobia; (4) alcohol abuse or dependence; (5) nicotine dependence; and (6) other drug abuse or dependence (excluding marijuana). Based on Meier et al. (2012), persistence of regular marijuana use in adulthood was defined as the total number of study waves in adulthood at which participants reported using marijuana 4 days/week or more, in addition to whether or not participants began weekly use in adolescence (assessed ages 14 thru 18). To examine onset and persistence of regular use, we categorized participants into 5 mutually exclusive groups: (1) adolescence limited regular use, (2) adolescent onset with continuing adult regular use (3) adult onset of regular marijuana use, (4) non-regular use, and (5) non-use. Analyses controlled for demographics and prior environment and behaviors including gender, poverty and ethnicity; a set of environmental controls indexing negative family, peer and neighborhood environments; and a set of individual risk controls including behavioral inhibition, disinhibition, internalizing and externalizing problems and academic achievement (assessed ages 10 through 14). Models examining consequences of marijuana use on adult substance use also controlled for adolescent use of that substance.

Results and Conclusions: Preliminary results from logistic, Poisson and negative binomial regressions indicate that the persistence of regular marijuana use is positively related to both symptom counts and the probability of meeting diagnostic criteria for generalized anxiety disorder, alcohol use disorder, nicotine dependence and other drug use disorders at age 33 even after controlling for the aforementioned confounds. Non-users of marijuana were generally better off than any of the four categories of marijuana users. Results from sensitivity analyses including alternate thresholds for defining regular use will also be presented. The discussion focuses on the prevention implications of findings from this study in the context of the recent marijuana-related legislative changes in Washington State and Colorado.