A study published in the journal Traffic Injury Prevention found that although occasional marijuana users had more difficulty maintaining driving control than nonusers, this is not true of daily users, particularly when consuming high-THC products.
Researchers from the University of Colorado Anschutz Medical Campus, Colorado State University, and Emory University examined the driving performance of 118 adults using a driving simulator before and after cannabis use. Participants completed one baseline drive and two post-use drives, approximately 30 minutes and 90 minutes after inhaling either marijuana flower or concentrate.
Among those who used marijuana—89 participants in total—occasional users of flower products showed a marked increase in lane departures shortly after use, jumping from 0.16 to 0.47 departures per minute. This was not observed in daily users of flower or concentrates, suggesting a possible tolerance effect.
Notably, the group that used high-THC concentrates on a daily basis actually demonstrated improved lane position stability after cannabis use, with a reduction in standard deviation of lateral placement. In contrast, the control group—who did not consume cannabis—showed a slight decline in this measure.
Overall, the study found only modest changes in average speed or lane control across all groups, with daily users showing less impairment than occasional users. The results suggest that cannabis tolerance plays a role in driving performance among those who consume it.
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