Evidence regarding how drugs other than alcohol are associated to traffic accidents (TAs) has increased in recent years. In many settings, cannabis is the most frequent illicit drug detected among drivers, and its prevalence is typically lower among drivers on the road, compared to injured drivers. Most case-control studies have found an increased chance of TAs among individuals who tested positive for cannabis. However, the findings depend on which cannabis components are analyzed, and whether the results originated from the analysis of blood, oral fluid, or urine. Whole blood sampling is the most effective confirmatory test, although the most accessible matrix for the roadside detection is oral fluid. Given the difficulties in establishing impairment based on toxicological tests, countries are struggling to enact legislation that regulates driving under the influence of cannabis. Overall, the laws that regulate driving under the influence of psychoactive and illegal drugs also regulate driving under the influence of cannabis.
