Cannabis use as a risk factor for causing motor vehicle crashes: a prospective study (2019)

AIM: We conducted a responsibility analysis to determine whether drivers injured in motor vehicle collisions who test positive for Delta-9-tetrahydrocannabinol (THC) or other drugs are more likely to have contributed to the crash than those who test negative.
DESIGN: Prospective case-control study.
SETTING: Trauma centres in British Columbia, Canada.
PARTICIPANTS: Injured drivers who required blood tests for clinical purposes following a motor vehicle collision.
MEASUREMENTS: Excess whole blood remaining after clinical use was obtained and broad-spectrum toxicology testing performed. The analysis quantified alcohol and THC and gave semiquantitative levels of other impairing drugs and medications. Police crash reports were analysed to determine which drivers contributed to the crash (responsible) and which were 'innocently involved' (non-responsible). We used unconditional logistic regression to determine the likelihood (odds ratio: OR) of crash responsibility in drivers with 0 < THC < 2 ng/ml, 2 ng/ml <= THC < 5 ng/ml and THC >= 5 ng/ml (all versus THC = 0 ng/ml). Risk estimates were adjusted for age, sex and presence of other impairing substances.
FINDINGS: We obtained toxicology results on 3005 injured drivers and police reports on 2318. Alcohol was detected in 14.4% of drivers, THC in 8.3%, other drugs in 8.9% and sedating medications in 19.8%. There was no increased risk of crash responsibility in drivers with THC < 2 ng/ml or 2 <= THC < 5 ng/ml. In drivers with THC >= 5 ng/ml, the adjusted OR was 1.74 [95% confidence interval (CI) = 0.59-6.36; P = 0.35]. There was significantly increased risk of crash responsibility in drivers with blood alcohol concentration (BAC) >= 0.08% (OR = 6.00; 95% CI = 3.87-9.75; P < 0.01), other recreational drugs detected (OR = 1.82; 95% CI = 1.21-2.80; P < 0.01) or sedating medications detected (OR = 1.45; 95%CI = 1.11-1.91; P < 0.01).
CONCLUSIONS: In this sample of non-fatally injured motor vehicle drivers in British Columbia, Canada, there was no evidence of increased crash risk in drivers with Delta-9-tetrahydrocannabinol < 5 ng/ml and a statistically non-significant increased risk of crash responsibility (odds ratio = 1.74) in drivers with Delta-9-tetrahydrocannabinol >= 5 ng/ml.
FRANÇAIS :
Selon cette étude de l'Université de British Columbia (UBC), les conducteurs présentant de faibles niveaux de THC dans le sang ne présenteraient pas de risque plus élevé d'avoir un accident que les abstinents. L'auteur principal de cette étude sur cinq ans souligne que la loi canadienne, qui pénalise actuellement le fait de conduire avec plus de 2ng/ml de THC dans le sang, pourrait être abusive.
Les chercheurs de l'UBC sont arrivés à la conclusion que les lois réglementant le taux de THC résiduel maximum pour la conduite de véhicules seraient bien trop strictes, car les lois canadiennes de sécurité routière pénalisent actuellement les conducteurs surpris avec 2 à 5 nanogrammes/millilitre dans le sang en leur infligeant des amendes.
Cette étude publiée dans le journal Addiction a démontré que les niveaux de THC trouvés dans le sang, s'ils restent en dessous de 5 nanogrammes/ml, ne constituaient pas un facteur d'accroissement du risque d'accident chez la plupart des conducteurs. [Actualités des Addictions 02/09/2019]