Cannabis and Alcohol Exhibit Contradictory Effects on Driving Performance

Drivers increase their speed following the use of alcohol but reduce their speed following the use of cannabis, according to an assessment of real-world driving performance published in the journal Accident, Analysis & Prevention.

Consistent with driving simulator data, participants who consumed cannabis engaged in compensatory driving behavior. Researchers reported that “alcohol-involved trips showed increased proportions of speeding on primary and secondary roads, suggesting impaired judgment or compromised longitudinal vehicle control. In contrast, cannabis-positive trips had speeding proportions closely aligned with baseline conditions, likely indicating habituation or compensatory driving behaviors.”

The study’s authors concluded: “This study marks a significant advancement in impaired driving research by conducting the first large-scale, naturalistic analyses of cannabis, alcohol, and their combined use in real-world driving contexts. … Overall, this study contributes valuable real-world evidence to a field that has long relied heavily on experimental paradigms. It offers early estimates of how cannabis and polysubstance use may affect driving behavior and begins to bridge the gap between tightly controlled experimental studies and the complexity of real-world behavior. As cannabis legalization continues to expand and polysubstance use becomes increasingly common, efforts like this will be essential in shaping more informed, evidence-based traffic safety policies and public health strategies.”