Cannabis, Impaired Driving, and Road Safety: An Overview of Key Questions and Issues

Abstract

The road safety impact of cannabis has been a topic of much discussion and debate over the years. These discussions have been revitalized in recent years by initiatives in several jurisdictions to legalize non-medical cannabis. Canada became the second country to legalize non-medical cannabis use in October, 2018, preceded by Uruguay in December 2013. Road safety concerns were key issues in the Canadian government's deliberations on the issue. In this paper, we identify several key questions related to the impact of cannabis on road safety, and provide a consideration of the relevant literature on these questions. These questions cover several perspectives. From an epidemiological perspective, perhaps the central question is whether cannabis use contributes to the chances of being involved in a collision. The answer to this question has evolved in recent years as the ability to conduct the relevant studies has evolved. A related question is the extent to which cannabis plays an important role in road safety, and recent research has made progress in estimating the collisions, injuries, and deaths that may be attributed to cannabis use. Several questions relate to the behavioral and pharmacological effects of cannabis. One central question is whether cannabis affects driving skills in ways that can increase the chances of being involved in a collision. Another important question is whether the effects of the drug on the driving behavior of medical users is similar to, or different from, the effects on non-medical users and whether there are sex differences in the pharmacological and behavioral effects of cannabis. Other important questions are the impact of tolerance to the effects of cannabis on road safety as well as different routes of administration (e.g., edibles, vaped). It remains unclear if there is a dose-response relationship of cannabis to changes in driving. These and other key questions and issues are identified and discussed in this paper.

Views on and experiences with medicinal cannabis among Canadian veterans who live with pain: A qualitative study

“…This echoes work by Gibson et al 55 who conducted a qualitative study on perceptions of alcohol and cannabis use among male Canadian veterans with PTSD ( N = 5) and observed that participants hesitated to use cannabis, even when medically prescribed, because they were concerned about how they may be perceived by their peers and society at large. As observed by Compton et al 63 stereotypes and biases about cannabis users continue to persist despite a general increase in the acceptability of cannabis use within society. It is common for veterans to experience self-stigma around cannabis use, 35 owing in part to deeply ingrained institutional military regulations and values prohibiting cannabis use.…”

The effect of cannabis edibles on driving and blood THC

“…Alternatively, the sample size in the present study was relatively small (Brands et al 2019, Marcotte et al 2022, but not unprecedented (Bosker et al 2012), and a lack of effect on other measures may reflect a lack of statistical power. Finally, this is the first study of edible cannabis on a driving simulator and it is possible that edibles have a different impact on driving than that following the smoked or vaped route, upon which current knowledge rests (Simmons et al 2022, Alvarez et al 2021, Brands et al 2021. Future converging evidence from emerging investigations will help to determine the impact of cannabis edibles on driving.…”

“…The results of driving simulator studies suggest that there is a dose-dependent alterations in driving (Ronen et al 2008, Hartman et al 2016 after cannabis, suggesting a relationship to blood THC. Studies so far have found increased 'weaving' (standard deviation of lateral position; SDLP) (Veldstra et al 2015, Ronen et al 2008, Hartman et al 2016, Bosker et al 2012, Simmons et al 2022, Arkell et al 2019, Arkell et al 2020, Alvarez et al 2021, Brands et al 2021) and changes in both speed (Ronen et al 2008, Hartman et al 2016, Simmons et al 2022, Alvarez et al 2021, Brands et al 2021, Di Ciano et al 2020, Brands et al 2019, Lenne et al 2010) and reaction time (Alvarez et al 2021, Brands et al 2021, Lenne et al 2010, Sewell et al 2009, Hartley et al 2019) following smoked cannabis. Important questions thus remain as to the impact of cannabis edibles on driving.…”

Risk Factors Associated With Driving After Marijuana Use Among US College Students During the COVID-19 Pandemic

“…The main psychoactive component of marijuana, active Delta-9-tetrahydrocannabinol (THC), had a significantly higher prevalence among seriously or fatally injured road users involved in motor vehicle collisions who presented at five US high-flow level 1 trauma centers and medical examiners during the pandemic compared to pre-COVID-19, and it was more prevalent among those road users during the COVID-19 pandemic compared to alcohol ( 34 ). Although research has shown that marijuana use impairs driving performance, including cognition, attention, reaction time, and vigilance ( 35 ), the effects of marijuana on driving performance are not predictable due to different individual characteristics (i.e., tolerance, frequent vs. occasional users) ( 36 , 37 ) and marijuana itself (i.e., dosage, administration route) ( 37 ). Additionally, in contrast to alcohol, which is more easily excreted from the body and has known limits for impairment, we have yet to determine a gold-standard for driving impairment following marijuana use and is still detectable in body fluids long after impairment has stopped ( 31 , 38 ).…”