Road accidents represent an important cause of deaths and injuries, and their prevention must be a priority. According to the World Health Organization, 1.35 million people died, and approximately 50 million people were injured from road traffic accidents worldwide in 2018 [
1]. One of the major causes of road accidents, particularly in Western countries, is the impairment of driving capabilities caused by the effect of psychotropic substances, drugs, and alcohol [
2,
3]. For instance, survey-based self-reported data suggest that in the US, 27.7 million people drove under the influence of alcohol and 10.1 million drove under the influence of illicit drugs in 2014 [
4]. Nevertheless, prevention has improved the situation in previous years, especially in Western countries. For instance, according to the Federal Statistical Office (OSF), in Switzerland, the number of victims of fatal accidents has significantly decreased in the last 26 years. Nevertheless, considering relative values, impaired drivers (either due to alcohol, illicit drugs or pharmaceuticals) were still responsible for a more or less constant percentage (16 to 25%) of fatal accidents between 1995 and 2018 [
5,
6]. In addition, the prevalence of psychoactive drugs within the global Swiss population is constantly increasing. Reports from the Swiss Federal Statistical Office show that 50% of the population aged above 15 years old were taking a pharmaceutical every week in 2017, compared to 38% in 1992 [
7]. The proportion of individuals taking pharmaceuticals increases with age, with 84% of the population aged over 75 years consuming pharmaceuticals weekly. In 2020, psychotropic drugs were the most prescribed drugs in Switzerland, representing 22.7% of all pharmaceuticals according to the Swiss Health Observatory [
8]. Within this category, antidepressants were the most prescribed drug. In 2018, the extrapolated one-year prevalence of benzodiazepines and z-drugs for the general Swiss population reached 10.5% [
9]. Switzerland is also one of the largest opioid and opiate consumer in the world, with prescriptions increasing by an average of 12% per year between 1985 and 2015 [
10]. Alcohol is one of the most widespread psychoactive substances, with 10.9% of the Swiss population reporting daily consumption and 15.9% reporting intermittent drunkenness. Regarding illicit drugs, in a study based on a self-report survey conducted in 2016, 7.3% of the population declared cannabis consumption within the last year, and 3.1% declared cannabis consumption within the last month. For cocaine, these values reached 0.7 and 0.1%, respectively [
11]. As individuals tend to underreport illicit and stigmatizing behaviours, these figures likely underestimate the actual prevalence of illicit drugs, particularly the consumption of cocaine. Furthermore, high frequency consumers of illicit drugs can be more difficult to reach using surveys, as they are often marginalised [
12]. Thus, the drug-consumer population is likely underrepresented in self-report surveys [
11].
The risk evaluation of driving under the influence of psychoactive substances is not an easy task. In many countries, including Switzerland, zero tolerance is applied concerning drivers towards classic illicit drugs [
13‐
15]. Nevertheless, the situation is much more complex regarding the toxicological interpretation of pharmaceuticals leading to driving impairments [
16]. Indeed, if many pharmaceuticals might lead to an enhancement of the risk of accident, the diversity of chemical properties and pharmacological effects do not allow a general statement on the driving abilities [
17]. Moreover, many people taking pharmaceuticals that could impair driving are not aware of the risks [
18]. According to Swiss law, the driving capability under these substances is determined by “a three pillars expertise”, including police assessment, medical expertise and toxicological analysis in blood [
15]. In Europe, the project Driving Under Influence of Drugs, Alcohol and Medicines (DRUID) showed a willingness to harmonise the classification of pharmaceuticals by providing scientific-based recommendations to driving under the influence of psychoactive substance issues [
19]. Therefore, to increase the understanding of Driving Under the Influence of Drugs (DUID) cases and improve both prevention and deterrent measures, a better understanding of the prevalence of the consumed substances and their toxicological effects is of interest.
Previous studies have shown significant differences in terms of substance distribution between samples collected from suspected drug-impaired drivers [
15,
20‐
23] and those collected in random approaches [
24‐
26]. Indeed, consumption habits are in constant evolution, and new substances, including new psychoactive substances (NPS), are arriving on the market. The variety of pharmacological effects complicates the identification of psychoactive substance consumption during preliminary on-site controls. Therefore, performing systematic sample collection and thus developing on-site, simple, and non-invasive sampling strategies for unbiased sample collection and more accurate knowledge of the prevalence of the consumed substances appears as an appropriate approach. Among those strategies, on-site collection of oral fluid (OF) has been indicated as a potential tool to evaluate DUID at roadside traffic controls [
27]. Dried blood spots (DBS) also provide an interesting alternative since only a limited volume of blood (10-20 μL) can be collected by either finger or heel pricking. The blood is adsorbed and dried on a solid phase (cellulose), and sample collection requires minimal training that can easily be performed in a nonmedical environment [
28‐
30].
This study aims to present the prevalence of driving under the influence of drugs in western Switzerland between 2006 and 2008 and 2017-2020. This study also provides insight into drivers’ perception of roadside controls and the bias associated with the current suspicion-based sampling procedures. The interest in the systematic use of on-site OF and DBS microsampling devices used by minimally trained technicians in a nonmedical environment is also discussed.