Cannabis smoking impairs driving performance on the simulator and real driving: a randomized, double-blind, placebo-controlled, crossover trial

Driving experiments in real conditions are considered as a gold standard' to evaluate the effects of drugs on driving performance. Several constraints are difficult to manage in these conditions, so driving simulation appears as the best alternative. A preliminary comparison is crucial before being able to use driving simulation as a valid evaluation method. The aim of this study was to design a driving simulation method for assessing drug effects on driving. We used cannabis (THC) as a positive control and assessed whether THC affects driving performance in simulation conditions and whether these effects are consistent with performance in real driving conditions. A double-blind, placebo-controlled, two successive two-way crossover design was performed using cigarettes containing 20mg of THC. Healthy occasional users of THC, aged 25-35years, who had a consistent driving experience were included. The first two sessions were realized in simulation conditions, and the last two sessions were in real driving conditions. Driving performance was estimated through inappropriate line crossings (ILC) and the standard deviation of the vehicle's lateral position. Participants felt significantly drowsier and more tired after THC, whatever the driving condition. Driving stability was significantly impaired after THC, both in simulated and real driving conditions. We also found that ILC were significantly more numerous in driving simulation conditions, as compared to real driving. In conclusion, the driving simulator was proven to be more sensitive for demonstrating THC-induced effects on driving performances. Driving simulation appears to be a good qualitative predictor of driving safety after drug intake.