Driving is a complex task where the driver continuously receives information, analyses it and reacts. Substances that have an influence on brain functions or on mental processes involved in driving will clearly affect the driving performance. Different studies provide information about the influence of illicit drugs and licit medicines on driving performance: They can be classified into three main types: epidemiological studies, pharmaco-epidemiological studies and experimental studies. Epidemiological studies are necessary to estimate the importance of the problem. They can be conducted in three different ways: · Descriptive epidemiological studies: the prevalence of psychoactive drugs in the driving population is determined on representative samples selected according to various criteria: the whole driving population, injured or killed drivers, drivers suspected of driving under the influence. The most important European studies are summarised in the report. · Responsibility analysis studies: in these studies, the authors try to determine the responsibility of drivers involved in road traffic accidents, to establish if drug use contributes to accidents or not. The responsibility is determined without knowledge of the results of the drug analysis. A study by Drummer (1045 killed drivers) and another one by Terhune (1882 killed drivers) are discussed as examples of responsibility analysis studies. · Studies with control groups: the results of the test group are compared with the same drug analysis performed on a control population consisting of matched drivers or non-responsible subjects. Very few epidemiological studies have included a control population. Pharmaco-epidemiological studies are very useful as they compare the number of accidents in drivers for whom medicines are prescribed with the number of accidents in a matched control population. The results of the major reports are summarised in the present work. However, this kind of study is difficult to perform with illicit drugs, for easily understandable practical and ethical reasons. Experimental studies consist in the administration of different doses of medicines or of placebo to selected volunteers. The effects on psychomotor performance and/or on driving skills are measured by laboratory tests, in driving simulators or by real driving experiments. While there is an abundant literature on the subject, methodologies are not well standardised and comparisons of different studies with sometimes conflicting results are difficult to perform. Illicit drugs possibly influencing driving performances are then presented, with epidemiological and experimental data if available: · Cannabis (used as marihuana, hashish, …) influences perception, psychomotor performance, cognitive and affective functions. This will affect co-ordination, vigilance and alertness, and will impair driving ability. The impairing effects are concentrated in the first 2 hours, but may persist for more than 5 hours. Real driving tests were only performed with low doses and show that a dose of 100—300 µg tetrahydrocannabinol /kg body weight has an effect comparable to blood alcohol concentrations of 0.3-0.7 g/L. Drivers seem to compensate their driving behaviour; however problems may arise in emergency situations. Impairment is more important and persistent for difficult tasks needing continuous attention. One study showed that injured drivers who were positive for cannabis were 2.5 times more likely to be killed. Responsibility analysis showed a trend towards a decrease in relative risk. · Opiates (mostly heroin) induce sedation, indifference to external stimuli, increased reaction time. Miosis has a negative effect on accommodation, mainly in darkness. Impairment of driving performance will be noted, even during the withdrawal syndrome, which is associated with a significant loss of concentration. There are no experimental data on the effect of heroin on driving performance. · Cocaine (free base, crack,…) is also incompatible with safe driving. There are no experimental data on cocaine and driving. The subjectively experienced performance improvement during the phase of euphoria will lead to increased risk-taking in traffic. The objectively observed performance impairment is due to a loss of concentration and attentiveness, and an increased sensitivity for blinding by light (dilated pupils). Moreover the psychological symptoms such as paranoia, delusions, hallucinations will have an influence on driving behaviour. · There are few studies of the influence of amphetamines and designer amphetamines (XTC, Eve, ….) on psychomotor function. These stimulating drugs will dangerously increase the self-confidence of the driver with increased risk-taking in traffic. The user becomes aggressive in the beginning and apathetic when the product disappears from the blood. Moreover, the wide pupils can cause blinding. Case reports show that amphetamines have a negative influence on the performance capabilities. However, in many cases of psycho-stimulation, it is not the acute effect of the drug but rather the exhaustion and overexertion resulting from the stimulation as well as other problems arising from misuse that are decisive for driving impairment. · Finally, hallucinogens (GHB, LSD, magic mushrooms, mescaline,…) impair psychomotor performance, by producing hallucinations, sleepiness, psychotic reactions,… which are not compatible with safe driving. Medicinal drugs affecting driving performance are finally presented. Psychoactive medicines can modify behaviour and experience, causing somnolence, loss of psychomotor co-ordination, balance or sensory disturbances,… · Benzodiazepines: with only one exception, all pharmaco-epidemiological studies show an increased accident risk in benzodiazepine-users. The highest risk is observed in the first weeks of treatment, with long-acting benzodiazepines and in young males. · Antidepressants: some, but not all pharmaco-epidemiological studies have shown that there is a dose-dependent increased risk for injurious crash. Newer antidepressants seem to be less impairing. · Neuroleptics are often sedative and induce motor disturbances and a decline of cognitive functions. · Narcotics and opioid analgesics produce sedation, impairment of cognitive functions, mood changes (dysphoria and euphoria), impairment of psychomotor functions and pupil restriction. Absolute driving unfitness exists at onset of the treatment, when important changes in drug dose are introduced and when other CNS depressants or alcohol are co-ingested. In long-term stabilised opioid therapy with unchanged doses no impairment of driving behaviour is observed. Pharmaco-epidemiological studies yield contradictory results. · Antihistamines can impair driving by the sedation they produce. However, newer (second generation) antihistamines cause very little sedation and are likely to have little impairing influence on driving. Some classifications have been proposed to categorise medicinal drugs according to their influence on driving ability (categories ranging from no impairment to severe impairment): the system proposed by the Dutch study group of Wolschrijn provides a categorisation of about 570 drug doses/formulations and the BLT in Belgium has classified 180 medicines. The use of categorisation and warning (sticker or label) systems in different European countries (Germany, the Netherlands, the Nordic countries, Italy, France) is discussed and finally, a comparison of the different systems is presented in an overview table. (A) For more information see http://www.rosita.org/
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