The Integrated Project DRUID (Driving under the Influence of Drugs, Alcohol and Medicines) involved researchers from more than 20 European countries. It aimed to gain new insights to the degree of impairment caused by psychoactive drugs and their actual impact on road safety. Part of this large research program that was conducted between 2006 and 2011 has been devoted to the assessment of stimulant drug effects on driving performance in experimental, placebo-controlled studies. These studies are presented in the current issue of psychopharmacology and focus on single-dose effects of MDMA (Bosker et al. 2012) and dexamphetamine (Hjalmdahl et al. 2012) on driving performance before and after a night of sleep deprivation and on the effects of MDMA (Veldstra et al. 2012) and dexamphetamine (Simons et al. 2012) with and without alcohol. The major objective of these studies was to provide scientific basis for harmonized pan-European regulations of driving under the influence (DUI) of stimulants. Research partners agreed on a number of standardized driving scenarios to increase comparability between studies. These included a road tracking test to measure standard deviation of lateral position (SDLP) or “weaving motion” during prolonged highway driving (O'Hanlon et al. 1982), a car-following scenario to measure a driver's ability to adapt to manoeuvres of other motorists (Brookhuis and de Waard 1993; Ramaekers and O'Hanlon 1994), and in case of driving simulator studies, risk-taking scenarios. In addition, all partners included a number of laboratory tests measuring skills related to driving. These tests included tracking tasks, attention tasks, reaction tasks, and cognitive tasks. Significant drug effects were statistically evaluated for clinical relevance by equivalence testing. Equivalence testing of drug effects was based on difference in scores from placebo relative to an alcohol criterion (i.e., equivalence to a blood alcohol concentration (BAC) of 0.5 mg/mL). Basically, equivalence testing assessed whether the alcohol criterion value falls within the 95 % confidence interval (CI) for the drug effect. If yes, then the drug effect was considered equivalent to a BAC of 0.05 mg/mL (and thus clinically relevant for traffic safety). If the 95 % CI was below the alcohol criterion value, then a drug effect was considered not relevant. An integrative overview of results from the four experimental studies is presented in Tables 1 and 2 of this article. (Author/publisher)
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