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.
- driving under the influence
- substance abuse detection
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Contributors FH-G, FJA, JCG-L and MC participated in the research design. MG-M performed the data analysis. FH-G and FJA wrote the manuscript. All the authors contributed to and approved the final version of the manuscript.
Funding This work was supported by the Instituto de Salud Carlos III, Redes Temáticas de Investigación Cooperativa, and Red de Trastornos Adictivos (grant number RD16/0017/0006) and co-funded by the European Regional Development Fund (ERDF)—a way to build Europe.
Competing interests All the authors have completed the International Committee of Medical Journal Editors (ICMJE) uniform disclosure form and declared no support from any organisation for the submitted work, no financial relationships with any organisations that might have an interest in the submitted work in the previous 3 years, and no other relationships or activities that could appear to have influenced the submitted work. MC and JCG-L are employees of the Dirección General de Tráfico, but this activity does not conflict with this national institution.
Patient consent for publication Not required.
Ethics approval The study was approved by our ethics review board (CEIC/CEIm Área de Salud Valladolid Este) on 28 September 2017 (Reference number PI 17-812). All methods were performed according to relevant guidelines and regulations and in compliance with the Declaration of Helsinki, Fortaleza, Brazil, October 2013.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available on reasonable request. All data relevant to the study are included in the article or uploaded as supplementary information.
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