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Cannabis and Motor Vehicle Crashes: A Culpability Study

Hours Posted on Hours Updated on

Author(s): Brubacher

Slidedeck Presentation Only (no paper submitted):

2A - Brubacher - Cannabis and MVCs

Abstract:

Acute cannabis use impairs the skills required for safe driving and many drivers use cannabis. Most research suggests that acute cannabis use approximately doubles the risk of crashing, although some recent studies suggest that the risk may be lower. Accurate estimates of the crash risk after cannabis use are required to guide traffic policy. This study uses a culpability analysis approach to study the risk of causing a crash in drivers who used cannabis prior to the event. This study is approved by the University British Columbia Research Ethics Board. We studied injured drivers who were treated in a BC trauma centre following a motor vehicle crash and who required blood tests for clinical purposes. 'Left over' blood that remained after clinical use was obtained from the hospital laboratory, labelled with a study ID number and frozen for later toxicology analysis. Broad spectrum toxicology testing was performed at the BC Provincial Toxicology Centre. The analysis quantified alcohol, THC, and COOH-THC and gave semi-quantitative levels of other impairing drugs and medications. Corresponding police crash reports were analyzed to determine which drivers contributed to causing the crash (culpable) and which were 'innocently involved' (non-culpable). We used unconditional logistic regression to determine the likelihood (Odds Ratio) of being deemed culpable in drivers with THC detectable, THC > 2 ng/mL, and THC > 5 ng/mL versus those with THC not detectable. Risk estimates were adjusted for driver age and gender, presence of alcohol or other drugs, comorbidities (mental/physical health), hospital site, type of crash (single vs multi-vehicle), and time of crash (day versus night). We obtained blood samples and toxicology results on 3006 injured drivers. Corresponding police reports were available in 2319 of these. Culpability results are being analyzed. We will report crude and adjusted odds ratios and 95% confidence intervals for THC detectable, THC > 2 ng/mL, and THC > 5 ng/mL. blank We will discuss the significance of our findings and compare our findings to other research in this field.