Cannabis and driving – daily consumers show no significant changes in performance

A new study has revealed that daily cannabis consumers displayed insignificant changes in driving performance when compared to non-users following inhalation.

The researchers, who are affiliated with the University of Colorado Boulder, assessed driving simulator performance among participants with daily use, occasional use and no history of cannabis use.

Participants inhaled cannabis over a 15 minute period then took part in simulated driving 30 minutes later. The researchers focused on their abilities to maintain lateral positioning and maintain a safe speed when compared to non-users.

Those with a history of occasional cannabis use exhibited a significant increase in SDLP (standard deviation in lateral positioning) following inhalation. Lateral positioning refers to the distance between the centreline and the nearest edge of the vehicle. The occasional users also drove faster than the non-user but not to a degree that was statistically significant.

Driving results

The daily users reported insignificant changes to SDLP following the inhalation and drove at slightly slower speeds.

The authors wrote: “In this study of the acute effects of cannabis use on driving performance among participants with a history of using cannabis daily or occasionally, we found evidence for decrements of driving performance in both groups relative to baseline for SDLP, that was of moderate size and statistical significance only in the occasional users. Small, statistically significant decreases in speed were observed in the daily use group.”

Previous study findings may confirm that elevated THC levels in the blood are not predictive or either increased poor driving performance or outcomes. Among the daily users, the mean THC blood levels were six times higher than they were for the occasional users despite only small differences in their driving performances.

The data was published in the journal Accident Analysis and Prevention.

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