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

AIMS: To test whether speed of transition from first 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: 2239 twins and siblings who reported using cannabis at least twice (mean age at time of survey = 32.0, 95% CI 31.9 - 32.1, range 22-45).

MEASUREMENTS: Time between first and subsequent cannabis use (within 1 week; within 3 months; between 3 months - 12 months; more than 1 year later), later use of cannabis and symptoms of DSM-IV cannabis abuse/dependence. Multinomial regression analyses (comparison group: more than 1 year 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 one week of first use was associated with daily use (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 3 months 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.