The effects of dexamphetamine on simulated driving performance

Rationale: The number of road fatalities related to the presence of amphetamines in drivers has been relatively constant over the past 10 years. However, there remains uncertainty as to the extent that these drugs induce driving impairment, and whether any such impairments translate to an increase in road fatalities. Objectives: To examine the acute effects of 0.42 mg/kg dexamphetamine on simulated driving performance, and to establish which, if any, simulated driving abilities become impaired following dexamphetamine administration. Methods: A repeated-measures, counter-balanced, double-blind, placebo-controlled design was employed. Twenty healthy volunteers completed two treatment conditions - 0.42 mg/kg dexamphetamine and placebo. Performance was assessed using a driving simulator task. Blood and saliva samples were obtained prior to the driving tasks and immediately after task completion ( 120 min and 170 min post-drug administration, respectively). Results: Mean dexamphetamine blood concentrations were 83 ng/ml and 98 ng/ml at 120 min and 170 min, respectively. Results indicated a decrease in overall simulated driving ability following dexamphetamine administration during the day-time but not the night-time scenario tasks. Contributing to this performance reduction, "incorrect signalling", " failing to stop at a red traffic light" and " slow reaction times" were the behaviours most strongly affected by dexamphetamine. Conclusions: The decrease in simulated driving ability observed during the day-time driving tasks are consistent with the perceptual narrowing or tunnel vision that is associated with dexamphetamine consumption.