Abstract
Background
Cannabis is known to have detrimental effects on human performance and may also affect driving adversely. However, studies designed to examine this issue have provided equivocal findings. We set up this study to further determine the effect of cannabis on driving.
Methods
We used a cross-sectional, case-control design with drivers aged 20–49 who were involved in a fatal crash in the United States from 1993 to 2003; drivers were included if they had been tested for the presence of cannabis and had a confirmed blood alcohol concentration of zero. Cases were drivers who had at least one potentially unsafe driving action recorded in relation to the crash (e.g., speeding); controls were drivers who had no such driving action recorded. We calculated the crude and adjusted odds ratios (ORs) of any potentially unsafe driving action in drivers who tested positive for cannabis but negative for alcohol consumption. In computing for the adjusted OR, we controlled for age, sex, and prior driving record.
Results
Five percent of drivers tested positive for cannabis. The crude OR of a potentially unsafe action was 1.39 (99% CI = 1.21–1.59) for drivers who tested positive for cannabis. Even after controlling for age, sex, and prior driving record, the presence of cannabis remained associated with a higher risk of a potentially unsafe driving action (1.29, 99% CI = 1.11–1.50).
Conclusion
Cannabis had a negative effect on driving, as would be predicted from human performance studies. This finding supports the need for interventions to decrease the prevalence of driving under the influence of cannabis, and indicates that further studies should be conducted to investigate the dose-response relationship between cannabis and safe driving.
MeSH terms: Cannabis, accidents, traffic, alcohol drinking, automobiles
Résumé
Contexte
On sait que le cannabis a des effets nuisibles sur les performances humaines et qu’il pourrait aussi nuire à la conduite d’un véhicule. Cependant, les études sur le sujet donnent des résultats peu probants. Dans notre étude, nous avons cherché à approfondir la question des effets du cannabis sur la conduite.
Méthode
Nous avons mené une étude cas-témoin transversale auprès de conducteurs de 20 à 49 ans impliqués dans des accidents mortels aux États-Unis entre 1993 et 2003; nous n’avons inclus que les conducteurs ayant fait l’objet d’un test de dépistage du cannabis, mais dont le taux d’alcoolémie était nul. Les cas étaient des conducteurs ayant commis au moins un acte de conduite potentiellement dangereux dans le contexte de l’accident (p. ex., dépasser la limite de vitesse); les témoins étaient des conducteurs dont la conduite n’avait pas été dangereuse lors de l’accident. Nous avons calculé les rapports de cotes (RC) bruts et ajustés de tout acte de conduite potentiellement dangereux chez les conducteurs déclarés positifs pour le cannabis, mais négatifs pour la consommation d’alcool. Dans notre calcul des RC ajustés, nous avons tenu compte de l’âge, du sexe et du dossier de conduite antérieur.
Résultats
Cinq p. cent des conducteurs avaient été déclarés positifs pour le cannabis. Le RC brut d’un acte de conduite potentiellement dangereux était de 1,39 (IC de 99 % = 1,21-1,59) pour les conducteurs déclarés positifs. Même compte tenu de l’âge, du sexe et du dossier de conduite antérieur, la présence de cannabis demeurait associée à un risque plus élevé d’avoir eu une conduite potentiellement dangereuse (1,29, IC de 99 % = 1,11-1,50).
Conclusion
Le cannabis a eu un effet néfaste sur la conduite, comme on pouvait le prédire d’après les études de performance humaine. Cette constatation confirme la nécessité d’intervenir pour réduire la prévalence de la conduite avec facultés affaiblies par le cannabis et montre qu’il faudrait pousser la recherche sur la relation dose-réponse entre le cannabis et la prudence au volant.
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