Drivers who tested positive for cannabis in oral fluid: a longitudinal analysis of administrative data for Spain between 2011 and 2016

ObjectivesThis study aimed to assess the association between positive roadside tests for delta-9-tetrahydrocannabinol (THC) and other driving-impairing substances and THC concentrations and the age and gender of THC-positive drivers.DesignThis study is based on administrative data.Setting, participants and exposuresNational administrative data on drivers who tested positive in confirmation analysis of driving-impairing substances in oral fluid were assessed (2011–2016, 179 645 tests).Primary and secondary outcome measuresFrequencies of positivity for THC, THC alone and THC plus non-THC substances (stratification by age and gender in 2016) and THC concentration were obtained. Comparisons and univariate and multivariate regression analyses were performed.ResultsOf the 65 244 confirmed drug-positive tests, 51 869 were positive for THC (79.5%). In 50.8% of the THC-positive tests, cocaine and amphetamines were also detected. Positivity for THC and non-THC substances predominated among drivers with low THC concentrations and represented 58.6% of those with levels lower than 25 ng/mL. The mean±SD for age was 29.6±7.7 years (year 2016, n=24 941). Men accounted for 96.3% of all THC-positive drivers. With increasing age, positivity for THC decreased (OR 0.948; 95% CI 0.945 to 0.952; p