Cannabis-Impaired Driving: A Public Health and Safety Concern

Cannabis, the most common illicit drug identified in motor vehicle crashes, had a higher prevalence than alcohol in drivers' blood or oral fluid specimens in the US in the 2013–2014 National Roadside Study (1). In fact, the percentage of weekend nighttime drivers with measureable Δ9-tetrahydrocannabinol (THC)2 in blood or oral fluid increased to 12.6%, a 48% increase since 2007 (2). Cannabis use is increasing since the legalization of cannabis in 4 US states and the approval of medical cannabis in 23 US states and many countries. The incidence of THC-impaired driving increased in Washington state from 19.1% before to 24.9% after cannabis legalization (3). These statistics highlight an important public health and safety concern: cannabis-impaired driving. In this issue of Clinical Chemistry, for the first time, Andrews et al. compare cannabinoid blood concentrations in fatal road traffic collision (RTC) victims with non-RTC victims in London and southeast England from 2011 to 2013 (4). Drivers' postmortem cannabinoid concentrations were reported previously from driver culpability studies (5), comparing the prevalence of cannabinoid-positive biological samples in culpable drivers to those not judged culpable for the crash. However, blood cannabinoid concentrations in postmortem non-RTC victims from the same population base are rarely available.