The association between speed of transition from initiation to subsequent use of cannabis and later problematic cannabis use, abuse and dependence

Abstract

Aims: To test whether speed of transition from initiation use to subsequent use of cannabis is associated with likelihood of later cannabis dependence and other outcomes, and whether transition speed is attributable to genetic or environmental factors. Design: Cross-sectional interview study. Setting: Australia. Participants: A total of 2239 twins and siblings who reported using cannabis at least twice [mean age at time of survey=32.0, 95% confidence interval (CI)=31.9 - 32.1, range=22-45]. Measurements: Time between initiation and subsequent cannabis use (within 1week; within 3months; between 3 and 12months; more than 1year later), later use of cannabis and symptoms of DSM-IV cannabis abuse/dependence. Multinomial regression analyses (comparison group: more than 1year later) adjusted the association between speed of transition and the outcomes of cannabis daily use, abuse/dependence and treatment-seeking after controlling for socio-demographic, childhood, mental health, peer and licit drug factors. Twin modelling estimated the proportion of variance in transition speed attributable to genetic (A), common environment (C) and unique environmental (E) factors. Findings: Subsequent use of cannabis within 1week of initiation was associated with daily use [odds ratio (OR)=2.64, 95% CI=1.75-3.99], abuse and/or dependence (OR=3.25, 95% CI=2.31-4.56) and treatment-seeking for cannabis problems (OR=1.89, 95% CI=1.03-3.46). Subsequent use within 3months was associated with abuse and/or dependence (OR=1.61, 95% CI=1.18-2.19). The majority of the variation of the speed of transition was accounted for by unique environment factors (0.75). Conclusions: Rapid transition from initiation to subsequent use of cannabis is associated with increased likelihood of subsequent daily cannabis use and abuse/dependence.