Acute cannabis consumption and motor vehicle collision risk: A systematic review of observational studies

Impaired driving is a leading cause of preventable morbidity and mortality in Canada, and is a tremendous burden on health care. Recent evidence has shown cannabis as playing an important role in road safety. Surveys have demonstrated that driving under the influence of cannabis has caught up to, and in some instances passed, rates of driving under the influence of alcohol in many jurisdictions, while collision studies have found that the rate of cannabis in the blood of injured and fatally injured drivers has increased in recent years. Despite this, research findings on the effects of cannabis on driver impairment and collision risk have been mixed. Some studies suggest cannabis use increases the risk of a collision while others suggest no effect or a decreased risk. To date, no formal synthesis of the available evidence has been completed and only one literature review has been published in 1999. Over one dozen new observation studies have been published in the preceding years, with more under way. For government to combat drug impaired driving necessitates the availability of a solid evidence base to inform policy development. To address this shortcoming, we propose to complete a systematic review and meta analysis of the observational epidemiological literature to answer the question: Does the acute consumption of cannabis (cannabinoids, THC) among drivers increase the risk of a motor vehicle collision? We will employ standard systematic review and meta-analysis methods as advocated by the Cochrane Review group, including the literature search, study selection, data extraction and risk of bias assessment, analysis and reporting. If warranted by the evidence, a meta analysis will be performed. Our primary goal is the translation of evidence from this research into the development of provincial policy and programs to improve road safety. We will also engage other federal and provincial stakeholders to be involved in the dissemination and uptake of the research.