Comparison of the prevalence of alcohol, cannabis and other drugs between 900 injured drivers and 900 control subjects: results of a French collaborative study
Introduction
Most drugs that affect the central nervous system may have the potential to impair driving ability. Alcohol, drugs of abuse (DOA: opiates, amphetamines, cocaine and cannabis) and prescribed psychoactive drugs are potentially concerned. For many years, attention has primarily focused on alcohol and most countries have established legal limits for blood alcohol concentration during driving. However, during the last years drugs other than alcohol have attracted increasing attention, due to a dramatic increase of use, particularly for cannabis which is by far the most consumed DOA in France as well as in many other countries. Research on the impairing effects of these psychoactive compounds has included several approaches [1]. Some studies have evaluated the effects of drugs on cognitive and/or psychomotor tasks after controlled administration [2], [3], [4]. Others have investigated drugs effects in situations mimicking real driving such as driving simulators [5], [6] and closed or open-road driving trials [7]. All these studies highlighted the increased risk of road crashes for drivers under the influence of these drugs, but did not provide the magnitude of the problem nor quantify accident risk. It is the reason why a very large number of epidemiological studies have been performed in many countries. Most of them have been focused on the determination of the prevalence of drivers involved in fatal or non-fatal motor vehicle accidents while being under the influence of drugs. However, the value of a number of these studies in measuring how frequently do people drive under the influence of drugs is weak, because they did not use appropriate analytical procedures [8], i.e. determination of the active forms of the main DOAs in blood, using sensitive and specific analytical procedures, with appropriate cut-off values. In France, for example recent studies have shown that the potentially impairing compounds most frequently found in blood samples from drivers involved in fatal and non-fatal accidents are respectively alcohol, cannabinoids and benzodiazepines [9], [10], [11]. This finding has also been observed in many other countries. When they use appropriate methodology, these observational studies are of interest because their results can lead the concerned countries to undertake appropriate prevention actions. However, a better knowledge of the role played by drugs in the occurrence of accidents is afforded when drivers are compared to a control group, but such case-control studies have seldom been performed. An Australian case-control study performed in injured drivers [12] revealed a significant relationship between alcohol, benzodiazepines and responsibility for the car crash, but this relation was not significant for cannabinoids and stimulants. However, the cut-off used in blood for cannabinoids was 40 ng/ml, which is by far too high [13], since THC blood concentrations decline rapidly down to a few ng/ml while impairing effects are still present [14].
The present article reports the results of a French multicentre study whose aim was to compare the prevalence of alcohol, drugs of abuse (cannabinoids, amphetamines, cocaine metabolites and opiates) and psychoactive therapeutic drugs in blood in two groups: one of 900 injured drivers and other of 900 age- and sex-matched controls.
Section snippets
Materials and methods
The emergency care units (ECU) and toxicology laboratories from six French university or general hospitals participated in the study: Grenoble, Le Havre, Limoges, Lyon, Poitiers, and Strasbourg. Blood was used as the biological matrix to screen for alcohol, cannabinoids, opiates, cocaine metabolites, amphetamines and psychoactive therapeutic drugs. The samples were collected from June 2000 to September 2001.
Results and discussion
The distribution according to age is presented in Table 1. Females represented 25.7% of the drivers.
Conclusion
This study confirms the high prevalence of the use and/or abuse of psychoactive compounds in the French population [23], [24]. This is particularly true for cannabis in the young population. Furthermore, our results demonstrate a higher prevalence of alcohol, cannabinoids and the combination of these two compounds in blood samples from drivers involved in road accidents than in those from controls and consequently suggests a causal role for these compounds in road crashes. These findings
Acknowledgements
This study was carried out with financial support from the French Ministry of Health, in the framework of a “Programme Hospitalier de Recherche Clinique National”. The authors are indebted to Nicolas Venisse, Yves Papet, Fabrice Mairot, Gisèle Lardet, Gérard Musiedlak and Patricia Briquet for their technical and/or scientific assistance.
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