Driving under the influence of cannabis: A 5-year retrospective Italian study

Cannabis consumption is associated with driving impairment and increased crash risk, endangering road safety. Toxicological analyses play a fundamental role in detecting a recent consumption of psychoactive substances. The aim of this study was to examine the concentration of cannabinoids in blood samples of driving-under-the-influence (DUI) offenders in order to investigate whether delayed sample collection affects the toxicological assessment of the offenders.

An observational retrospective study was performed using anonymized toxicological data referring to cannabis-related DUI offenders involved in road traffic accidents (RTA) or apprehended by the police from 1 January 2017-31 December 2021 archived at Legal Medicine and Toxicology Department of the University Hospital of Padova, Italy.

In a total sample of 318 drivers, 143 blood samples tested positive for tetrahydrocannabinol (THC) and metabolites 11-hydroxy-Δ9-tetrahydrocannabinol (11-OH-THC) and 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH), and 173 blood samples were positive for THC-COOH with THC negative. In the first group, the mean concentrations of THC and THC-COOH were 4.05 ng/mL and 28.29 ng/mL, respectively. In THC-negative cases, the mean THC-COOH concentration was 7.3 ng/mL. The time elapsed between the event and sample collection varied from 15 min to 7 h (mean 2 h 29 min). The average estimated time elapsed after consumption of cannabinoids was 3 h 7 min (Model I) and 2 h 36 min (Model II).

The present research discussed the main difficulties in the toxicological evaluation of drivers under the influence of Cannabis. Issues related to the time between RTA and sample collection, the laws and legal limits in force in various Countries were presented.