Commentary on van der Pol et al . (2014): Reconsidering the association between cannabis exposure and dependence

Abstract

The existence of a positive, and relatively strong, association between cannabis exposure/tetrahydrocannabinol (THC) dose and cannabis dependence is an assumption on which much cannabis-related research, public policy and health advice has been based. Van der Pol et al.'s [1] findings, however, throw this into some doubt. To understand why there is a discrepancy here, and its import, it is essential to consider how cannabis exposure/dose is typically measured and, thereby, how past studies may have clouded our understanding of the association between cannabis use and dependence. Cannabis exposure has been assessed in a variety of ways, tending to include measurement of some combination of age at first use, duration of use, quantity consumed and frequency of use, with the latter often employed in isolation as a proxy for THC dose [2]. Although known to be only approximations of exposure, these variables are used by researchers for a number of reasons. Foremost among these are the efficiencies associated with the use of self-report questionnaires, which are often completed anonymously by participants and remotely from researchers. The classification of cannabis as an illicit substance within most jurisdictions globally, however, also acts to prevent the vast majority of cannabis researchers from undertaking as thorough an assessment of cannabis exposure/dose as has been demonstrated by van der Pol et al. [1].