The effect of 5 mg of Diazepam on driving-related skills : equating impairment to a blood-alcohol concentration level, and investigating subjective perception of impairment

A mixed-measures research design was employed to investigate the effects of a single acute 5mg dose of diazepam on psychomotor performance and subjective experience. Following a doubleblind protocol, 34 benzodiazepine-naive participants were administered 5mg of diazepam or placebo. Tasks measuring the driving-related skills of psychomotor processing speed, sensory motor reaction time, vigilance, divided attention and tracking, as well as subjective alertness and subjective competence, were completed for 150 minutes post-ingestion. Deleterious effects of diazepam tended to peak at 60 minutes post-ingestion, with the largest effects being of a moderate magnitude. Psychomotor processing speed and vigilance were more deleteriously affected than sensory motor reaction time and divided attention. Dissociations between the alertness and competence ratings given before and after test battery completion suggest that self-monitoring accuracy may not be fully intact under the influence of the 5mg dose. A method for equating impairment to a blood-alcohol concentration (BAC) equivalency was trialled. This method involved the application of a regression equation to performance decrement measurements from the tracking task. The BAC equivalency of impairment found in the current study utilising this method was .041%, however it is recognised that this is likely to be an underestimation for older diazepam users and for people taking regular, repeated 5mg doses for the first several weeks. Consequently, many diazepam users may be impaired by diazepam to an extent considered risky for driving (more than .05% BAC). It is reasonable to suggest that Medical Practitioners should educate patients when prescribing diazepam, so that patients are aware of the steps they can take to reduce their crash risk when under the influence of diazepam.