The effects of cannabis and alcohol on driving performance and driver behaviour: a systematic review and meta‐analysis

Simmons, Sarah M.; Caird, Jeff K.; Sterzer, Frances R.; Asbridge, Mark · 2022 · OpenAlex-citations

DOI: 10.1111/add.15770

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Summary

This systematic review and meta-analysis investigates the mechanisms underlying the association between cannabis use and increased crash risk, a relationship previously established by epidemiological data but lacking experimental clarity. The study aims to quantify the magnitude of cannabis’s effect on driving performance and behavior, compare these effects to those of alcohol, assess the impact of combining both substances, and identify gaps in the existing literature. The research was motivated by the need to understand how cannabis specifically impairs driving to inform future high-quality research and policy. The authors conducted a systematic search of eight academic databases (including MEDLINE, PsycINFO, and Embase) in May 2018. Eligibility criteria included experimental driving studies involving healthy participants of any age or sex, utilizing driving simulators, closed-course, or on-road settings. Studies had to involve the administration of cannabis and/or alcohol and report driving performance or behavior data. From an initial pool of 120 eligible studies, 81 were included in the final meta-analysis. The study design involved synthesizing data on various metrics, including crashes, hazard reaction time, headway, lateral position variability, lane excursions, and speed. The results indicate distinct impairment profiles for cannabis and alcohol. Cannabis was primarily associated with impaired lateral control and a decrease in driving speed. In contrast, alcohol was linked to a broader variety of driving performance decrements and an increase in driving speed. When cannabis and alcohol were combined, the resulting driving performance decrements were greater than those caused by either substance in isolation. Indirect comparisons suggested that the effects of cannabis on experimental driving measures were generally similar to those of low blood alcohol concentrations. However, the authors note that imprecision in effect size estimates limits definitive interpretation, necessitating further research. The significance of this work lies in its confirmation that cannabis, like alcohol, impairs driving performance, with the combination of the two substances being particularly detrimental. The findings provide empirical evidence to support the understanding of cannabis-related driving risks, moving beyond epidemiological associations to specific behavioral mechanisms. The study also highlights the need for improved research quality and identifies specific directions for future investigations to reduce imprecision in effect estimates. By comparing cannabis to alcohol, the research offers a benchmark for understanding the severity of cannabis impairment, suggesting it is comparable to low-level alcohol intoxication in certain experimental contexts.

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Topics

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• polydrug
• cannabis
• alcohol
• illicit drugs