Conclusions are nearly identical to a study comparing drivers who abstained from cannabis for 48 hours to that of non-users
Cannabis consumers exhibit no next-day driving impairment despite having trace levels of THC in their blood, according to driving simulator data published in the Journal of Cannabis Research.
Canadian investigators assessed consumers’ psychomotor performance some 12 hours after they last inhaled cannabis. Their performance was compared to that of subjects with no history of marijuana use.
Participants in both groups exhibited similar driving performance. Despite showing no significant degree of impairment, consumers possessed mean concentrations of THC in their blood above 2ng/ml.
“Neither blood nor oral fluid THC, CBD, or metabolites was significantly correlated with any measure of driving,” the study’s authors concluded. “The regular cannabis use group showed no significant impairment in driving performance 12-15 hours after last cannabis use the night before, compared to the control group.”
Their conclusions are nearly identical to those of a recent UC San Diego study. In that study, investigators compared the driving performance of consumers who had abstained from cannabis for 48 hours to that of non-users. Both groups performed similarly, despite nearly half of the consumer group testing positive for THC in their blood.
NORML has consistently argued that neither the detection of THC nor its metabolites in bodily fluids is necessarily predictive of diminished performance. Alternatively, NORML has called for the expanded use of performance-based tests, like DRUID or Predictive Safety’s AlertMeter, which compare subjects’ cognitive skills to either their own prior performance or an aggregate baseline.
Full text of the study, “Driving by frequent cannabis users ‘the morning after’ last use of smoked cannabis: An observational driving simulator study,” appears in the Journal of Cannabis Research. Additional information on cannabis and driving is available from the NORML Fact Sheet, ‘Marijuana and Psychomotor Performance.’
