Associations between cigarette smoking and cannabis dependence: A longitudinal study of young cannabis users in the United Kingdom

Aims: To determine the degree to which cigarette smoking predicts levels of cannabis dependence above and beyond cannabis use itself, concurrently and in an exploratory four-year follow-up, and to investigate whether cigarette smoking mediates the relationship between cannabis use and cannabis dependence. Methods: The study was cross sectional with an exploratory follow-up in the participants' own homes or via telephone interviews in the United Kingdom. Participants were 298 cannabis and tobacco users aged between 16 and 23; follow-up consisted of 65 cannabis and tobacco users. The primary outcome variable was cannabis dependence as measured by the Severity of Dependence Scale (SDS). Cannabis and tobacco smoking were assessed through a self-reported drug history. Results: Regression analyses at baseline showed cigarette smoking (frequency of cigarette smoking: B = 0.029,95% CI = 0.01, 0.05; years of cigarette smoking: B = 0.159,95% CI = 0.05, 0.27) accounted for 29% of the variance in cannabis dependence when controlling for frequency of cannabis use. At follow-up, only baseline cannabis dependence predicted follow-up cannabis dependence (B = 0.274, 95% CI = 0.05, 0.53). At baseline, cigarette smoking mediated the relationship between frequency of cannabis use and dependence (B = 0.0168, 95% CI = 0.008, 0.288) even when controlling for possible confounding variables (B = 0.0153, 95% CI = 0.007, 0.027). Conclusions: Cigarette smoking is related to concurrent cannabis dependence independently of cannabis use frequency. Cigarette smoking also mediates the relationship between cannabis use and cannabis dependence suggesting tobacco is a partial driver of cannabis dependence in young people who use cannabis and tobacco. (C) 2015 The Authors. Published by Elsevier Ireland Ltd. This is an open access article under the CC BY license.