Research Papers

The Impact of Smoked Cannabis and Distraction on the Simulated Driving Behaviour of Young Recreational Cannabis Users

Version 1
Date added June 28, 2017
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Category 2017 CARSP XXVII Toronto
Tags Research and Evaluation, Session 6A
Author/Auteur Christine Wickens
Stream/Volet Research and Evaluation

Slidedeck Presentation Only (no paper submitted)



Recently proposed legislation to permit recreational cannabis use in Canada may have an impact on the prevalence of driving under the influence of cannabis (DUIC). Based on a 2013 report from the Centre for Addiction and Mental Health, past year cannabis use is significantly higher among Ontarians aged 18 to 29 years than any other age group. Recent research in the United States and Canada indicates that the prevalence of DUIC among young drivers of high school and university age and young adults is already similar to, or higher than, the prevalence of driving under the influence of alcohol. Several meta-analyses of the epidemiological literature have indicated that cannabis use is associated with increased motor vehicle collision risk. Previous research has suggested that one factor that may influence the impact of cannabis on driver behaviour is the level of distraction involved in the driving task, with effects being greater when driving is performed under distracted conditions. This factor may be particularly salient among young drivers. Given the pending legalization of recreational cannabis use, it is imperative that we improve our understanding of how cannabis use impacts driver behaviour and collision risk. The current study examined the effects of an acute dose of cannabis, with or without distraction conditions, on the driving-related skills of young drivers who use cannabis regularly. The study was a randomized, double-blind, placebo-controlled mixed design trial, including regular cannabis-using drivers, between the ages of 19–25 years, who smoke cannabis 1–4 days per week. Participants completed a practice session followed by a testing day. Measures of simulated driving performance, cognitive and psychomotor function, subjective drug effects and blood and urine samples were collected concurrently before and after a one-time ad libitum administration of smoked cannabis (approximately 12.5% (active) or <0.01% (placebo) THC). During each simulated driving trial, participants performed first under the no distraction condition, followed by a trial under the distraction condition. Distraction was introduced by requiring participants to count backwards by 3’s from a randomly chosen 3-digit number as fast as possible while performing the driving task. Data are currently being analyzed, but preliminary results provide evidence of changes in measures of driver behaviour, including mean speed and standard deviation of lateral position, among drivers with higher levels of THC in their blood, and that these changes may be affected by distraction conditions. Although extensive epidemiological research has identified an increased risk of collision associated with cannabis use, our knowledge of how driver behaviour is affected by cannabis has been limited. The robust experimental design of the current study, including the ability to assess the concurrent impact of distraction on how cannabis affects driving, will provide valuable new information on this issue. Preliminary analyses of the data have identified changes in driver behaviour associated with cannabis use, and suggests that these changes may be influenced by distraction conditions. These results highlight the importance of improved understanding of DUIC as Canada moves forward with legalization of recreational cannabis use.

Christine Wickens