Combined Alcohol and Cannabis Use on Driving

Is there really an increase in a crash risk when people consume cannabis before driving? New research suggests what many have already concluded in earlier research: cannabis does not increase the risk of a crash.

Choo et al. (2024) present a new study investigating the crash risk associated with alcohol and cannabis use, offering valuable insights into a topic of significant concern for public safety. In this study, the researchers conducted a well-designed U.S. case-control investigation to elucidate the individual and combined effects of alcohol and cannabis on the likelihood of drivers being injured in road crashes.

Building upon prior research by White and Burns (2021; 2022), who found no conclusive evidence of cannabis’s impact on crash risk, and their subsequent exploration of cannabis’s potential exacerbating effect on alcohol-related crashes (White & Burns, 2023), Choo et al.’s findings corroborate the notion that cannabis use alone does not significantly contribute to crash risk. Their study reveals a notable disparity between the effects of alcohol and cannabis: while alcohol alone substantially increases the risk of a crash, cannabis alone appears to have no discernible effect on crash likelihood.

A particularly noteworthy aspect of Choo et al.’s study is their investigation into the combined use of alcohol and cannabis, a scenario with potentially heightened risks. Surprisingly, the researchers found that the combined effect of alcohol and cannabis did not increase crash risk beyond that associated with alcohol alone. This finding challenges common assumptions that are made about driving impairment and underscores the importance of evidence-based policymaking in addressing impaired driving.

Not that we use much of that in Canada or British Columbia, it seems.

However, despite the significance of their findings, Choo et al. (2024) acknowledge several limitations inherent in their study. Notably, these include the unreliability of self-reported evidence of recent substance use, particularly given their disproportionate reliance on such data in their analyses. This reliance raises concerns regarding the accuracy of the findings and underscores the need for more robust methodologies in future research endeavours.

Moreover, the exclusion of benzodiazepines—a class of drugs known to pose a higher crash risk than cannabis—from the study’s scope represents a missed opportunity to comprehensively assess the impact of various substances on driving safety. By overlooking benzodiazepines, Choo et al. may have inadvertently limited the breadth of their findings and overlooked potential confounding variables that could influence crash risk assessments. We know that benzodiazepine drug use is significantly on the rise and the issues associated with this should be properly studied.

Ultimately, this study offers valuable insights into the complex relationship between alcohol, cannabis, and crash risk, shedding light on the nuanced interplay of these factors in determining driver safety. While their findings challenge conventional wisdom about combining alcohol and cannabis and its effect on crash likelihood, further research is necessary to fully explore this issue.

Addressing methodological shortcomings and expanding the scope of inquiry to encompass additional substances will be crucial steps in advancing our understanding of impaired driving and informing evidence-based interventions to enhance road safety.

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