Correlates of cannabinoid concentrations, real-world driving, and driving-related skills

Abstract Research on the relationship between cannabis use and safe driving has produced mixed results. Most studies have focused exclusively on the presence or concentration of delta-9-tetrahydrocannabinol (THC), the primary psychoactive ingredient in the drug. However, cannabis is a complex substance, and both toxicological research and user experience suggests that some cannabis strains—often those with at least moderate levels of cannabidiol (CBD)— produce a different, more sedating “high” than cannabis strains with no or low levels of CBD. We hypothesize that the sedating properties of some high-CBD cannabis strains has potential to impair driving and driving-related skills above and beyond the effects of THC intoxication. Three studies—one instrumented vehicle driving study and two laboratory-style epidemiological studies—examined real driving and computerized task performance as a function THC and CBD concentrations (and their interactions). In all three studies, higher CBD levels predicted greater impairment. There was relatively little evidence of impairment when CBD was zero, even at high THC levels. The results suggest that THC concentrations alone are not sufficient to predict impairment due to cannabis use. Results are interpreted in the context of drug tolerance.