The ongoing development of transportation methods has resulted in a more diverse population of drivers on the roads. At the same time, increased accessibility and a wider variety of newer medications, psychoactive substances, and alcohol create a potentially dangerous combination. Today, many individuals consume substances that can impair their ability to drive. These substances can be classified as either depressants—such as alcohol, benzodiazepines, opioids, THC—or stimulants like amphetamines, MDMA, PMMA, and cocaine. Depressants significantly impair reaction times, reduce concentration, cause dizziness, and hinder information processing [18,19,20,21,22]. In contrast, stimulants may lead to risky behaviours, aggressive driving, and difficulty in maintaining attention and focus. They can also cause hallucinations, disordered thinking, visual disturbances, and impaired coordination [23,24,25]. The concurrent use of multiple psychoactive substances markedly increases the likelihood and severity of these effects. Driving under such influence greatly heightens the risk of accidents and dangerous behaviour on the road [26].

According to our findings, THC was the most common substance detected in drivers—37.8% of positive blood samples. This aligns with recent studies from Denmark (2015–2016) [27], Italy (2014–2017) [28], and Hungary (2014–2015) [29], where THC was also the most frequently identified psychoactive substance aside from alcohol. Alcohol was next at 19.5% of samples. The number of blood alcohol-positive samples—32—may seem low considering that 2616 people in Podlasie Province were caught driving under the influence in 2024 [30]. This discrepancy can be attributed to the recent use of private laboratories for sobriety tests and the study’s focus on cases where authorities requested toxicology reports.

Amphetamine was the third-most commonly detected substance, accounting for 12.8% of samples, similar to previous findings where it followed THC [13]. Notably, opiate detection decreased from 15.9% to 2.4% [13]. An essential addition is a new category of drugs—stimulants established as synthetic substances, such as PMMA, alpha-PVP, and MDMA, which have become more popular on the Polish market. Known as legal highs, these psychoactive substances were first introduced around 2008, when the first specialised legal high shops began to appear on Polish streets. This phenomenon reached its peak in 2010, with over 1300 such shops in existence [31]. Along with the popularity of these substances among adolescents and school students, this led to legal changes that contributed to a decline in stimulant use. A steady decrease has been observed since 2011 [32]. Our analysis does not mirror the Polish trend, as stimulant use among the drivers we analysed peaked in 2017 and again in 2020–2021. Nonetheless, our results can be linked to an increase in the detection of new synthetic stimulants on the Polish market, which reached an all-time high in 2016, then decreased for some time before rising again in 2021 [32].

In our study, cocaine is overtaken by several other types of drugs. In Italy and Denmark, it ranks as the second-most commonly detected substance among drivers, at 7.2% [28] and between 27% and 28.5% [27] of all detections, respectively. Our results are consistent with European trends in psychoactive substance use. The European Union Drugs Agency report on cocaine states that the prevalence of cocaine in Poland is among the lowest in European countries [33].

Considering multidrug use, THC was used as often as amphetamine, with both appearing in combinations in 13 cases. Previously, amphetamine was combined with other substances in only 9 cases [13]. Alcohol was frequently mixed with stimulants, including amphetamine, in 6 cases. An Italian study reached a different conclusion, finding that in the Milan area, alcohol was most commonly paired with cocaine and cannabinoids [34]. Similar results to ours were observed by Gjerde et al. in Norway, where THC was the most frequently detected drug used in combination with other substances [35]. The most common substance combinations observed were THC with sedatives and stimulants (22.9%), THC with alcohol (14.1%), THC with sedatives alone (14.1%), and the combination of THC, alcohol, and sedatives (11.9%) [35]. An analysis carried out in the USA showed that the largest group of drivers under the influence was composed of those using alcohol alone (54.9%), followed by a group mixing alcohol with cannabinoids (36.5%) [36].

Maurer et al. over a period of two years (2018–2019) in Western Switzerland, identified one or more psychoactive drugs in 89.0% of cases [37]. In our study, we recorded only a few instances of this, which can be partly attributed to the fewer requests for comprehensive toxicology panels.

In our study, the highest BAC detected was 4.1‰ in a road traffic accident victim, a level considered life-threatening. The highest BAC measured during roadside surveys was 3.2‰. It is impossible to compare this to the previous study because at that time, samples were collected only from sober drivers. Ferrari et al. conducted a similar study in the Milan area, reporting the highest recorded BAC of 4.6‰ [34], and Maurer in Western Switzerland—recording a BAC of 3.8‰ [37].

The highest THC concentration recorded in our study was 20 ng/mL, found in the blood of a victim involved in a road traffic accident. This level exceeds the previously highest reported value of 12.3 ng/mL from a roadside survey, as documented in our previous study [13]. The maximum blood concentration reported by Maurer was 52.0 µg/L [37].

A Norwegian study found that 20.0% of drivers involved in crashes had blood THC levels above 1.3 ng/mL, which is the legal limit in their country. Concentrations exceeding 9.3 ng/mL (high sanction limit) were recorded in 14.8% of cases [35]. Italian research showed that over 75.0% of samples testing positive for THC were above the legal limit of 2 ng/mL [34].

Our analysis included blood concentrations of various stimulants, such as amphetamine, cocaine, PMMA, MDMA, alpha-PVP, and mephedrone. The highest amphetamine concentration was found in the blood of a road traffic accident victim, at 2997 ng/mL—over 27 times higher than the effective dose of 110 ng/mL. This significantly exceeds our previous research, where the highest recorded concentration was 155.2 ng/mL during a roadside survey [13]. Gjerde et al. documented almost 6.0% of cases where blood concentrations of amphetamine exceeded 487 ng/mL [35]. A different study conducted in Norway, published in 2024, recorded a median blood amphetamine concentration of 299.7 ng/mL [38], and a Swiss study, 1700.0 μg/mL [37].

Cocaine was detected at its peak blood concentration of 30.0 ng/mL during a roadside survey, while its metabolite, benzoylecgonine, reached 602.0 ng/mL in the blood of an accident survivor. Our previous work focused on the blood concentration of benzoylecgonine rather than cocaine itself, reporting a maximum concentration of 117.3 ng/mL [13]. In Switzerland, the highest recorded concentration of cocaine was 1500.0 µg/L, and benzoylecgonine 5400.0 µg/L [37].

The remaining substances are not reflected in our earlier work due to their relatively late introduction to the market and their growing popularity over time. PMMA’s highest blood concentration, 360.0 ng/mL, was found in a sample from a road traffic victim; otherwise, the highest blood concentration of MDMA (75.0 ng/mL) was obtained from a roadside survey. MDMA was also detected in a Swiss study, reaching a blood concentration of 1400.0 µg/L [37]. The highest blood concentrations of other stimulants were identified in blood samples from road traffic accident survivors: mephedrone (37.5 ng/mL) and alpha-PVP (120.0 ng/mL).

In this study, we measured blood concentrations of detected drugs and compared them to established therapeutic ranges and known toxic doses. The first group of prescription medications analysed comprised opiates. Notably, opiate concentrations in all cases remained within therapeutic ranges, and opiates were identified exclusively in individuals involved in road traffic collisions. This finding contrasts with our previous study, which observed similar blood concentrations of opiates among all examined groups of drivers. The second group included benzodiazepines, where only one sample exceeded the therapeutic range—midazolam at a concentration of 1200.0 ng/mL, detected in a sample from a survivor of a road traffic accident. Past research did not reveal any cases of benzodiazepine concentrations over the therapeutic range. A similar result was obtained by Maurer et al., with many instances exceeding the therapeutic range [15,37].

Additionally, several psychotropic medications were found in the analysed blood samples; however, all were within their therapeutic ranges, consistent with our previous findings [13].

In our paper, we chose to compare substance use among drivers of different vehicles, mainly between car drivers and motorcycle drivers. Due to the small number of non-car drivers, it is challenging to draw definitive conclusions. However, a Serbian study showed that nearly 23.0% of motorcycle drivers are under the influence, whereas only 0.8% of car drivers were under the influence [39].

We sorted our data to identify trends in substance abuse among drivers over the years. However, due to the small number of cases, most results are inconclusive. A notable decline in THC detections occurred after 2015, likely because authorities in Poland now use private laboratories. Since then, the number of positive samples has stabilised. This does not align with the national decline in THC use, observed since 2011 [31]. Our results also do not reflect national amphetamine trends. Usage among Polish citizens dropped rapidly between 2010 and 2014, then gradually increased [33], unlike our findings. General substance statistics may not directly mirror usage among drivers, but they remain relevant because government data often lacks a focus on driving under the influence. Statistics mainly emphasise alcohol-related driving. Alcohol consumption in the general population remained steady, apart from a slight increase in spirit-based drinks [32]. Except for 2017, our alcohol analysis produced consistent results. In contrast to the overall trend in Europe, alcohol-related driving did not decrease universally; a 2016 study in Campania, Italy, found a significant rise over eight years [40].

In our research, we chose to emphasise alcohol use; however, the small number of alcohol-positive samples limits interpretation. While alcohol is less likely to be used alone or with other substances in our findings, a US study found only 2.0% of respondents reported driving under the influence of multiple substances, though among those who drove under the influence, a significant proportion were polydrug users: 16.0% reported using two substances, and 3.5% reported using three or more [36].