Adult Psychiatric, Substance, and Functional Outcomes of Different Definitions of Early Cannabis Use.

Objective Research on associations of early cannabis use with adult functioning reports mixed findings. This may be due, in part, to wide variations in the definitions of early cannabis use. This study aims to compare associations of 4 commonly used definitions of early cannabis use—related to timing, dose, duration, and associated symptoms—with adult outcomes. Method Analyses were based on a 20+-year longitudinal, community-representative study of 1,420 participants. Between ages 9 and 21 years (8,806 observations), participants were assessed for cannabis use and DSM-5 Cannabis Use Disorder. In early adulthood (ages 24-26 and 30; 2,424 observations of 1,266 subjects), participants were also assessed for psychiatric, substance use, and functional outcomes. Results All definitions of early use were associated with multiple adult outcomes in models that adjusted for sex and race/ethnicity. In models that also adjusted for childhood psychiatric problems and family adversities, only daily use and a persistent developmental subtype (defined as daily/problematic use that began in adolescence and continued into early adulthood) were associated with later substance use/disorders, poorer functional outcomes, and derailments in the transition to adulthood. Conclusion Daily, continued-over-time cannabis use beginning on adolescence was most problematic for a range of adult outcomes. Cessation of early use did not fully eliminate later risks; but was associated with fewer negative outcomes, with weaker effect sizes.