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

OBJECTIVES: This 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. DESIGN: This study is based on administrative data. SETTING, PARTICIPANTS AND EXPOSURES: National 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 MEASURES: Frequencies 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. RESULTS: Of 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<0.0001), and positivity for THC and non-THC substances increased (OR 1.021; 95% CI 1.017 to 1.024; p<0.0001). Men were associated with higher THC concentrations (OR 1.394; 95% CI 1.188 to 1.636; p<0.0001). CONCLUSIONS: Cannabis positivity is frequent among drivers, and polysubstance use is common. Hence, focusing on younger drivers and those with low THC concentrations is encouraged. This study provides evidence on the current implementation of roadside drug testing in Spain and aims to characterise driving under the influence (DUI) of cannabis to increase the awareness of all involved to help them avoid DUI.