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Influence of medications on drivers. Research Report

14 July 2011

 Medications may influence the skills and processes required for safe driving, both positively and negatively, and this impact may differ among drivers. The aim of this DfT project was to examine the influence of prescription medication on driving, focusing on the impairing effects of different medications, individuals’ awareness of any impairment, and whether individuals taking medication alter their driving behaviour.

Main findings of the report (available here) are:

• It is difficult to quantify the effect of medication on road safety because of several data gaps, including a lack of information on the prevalence of prescription drugs in the driving population.
• There is a lack of a benchmark of impairment for medications, similar to that accepted for alcohol.
• Drugs from a number of classes impair driving or the cognitive functions likely to be associated with driving ability in healthy volunteers. However, driving ability may improve in patients if the medication alleviates symptoms of a condition that affects driving and/or, with repeated medication use, tolerance to impairing effects develops. Nevertheless, tricyclic antidepressants, benzodiazepine anxiolytics, neuroleptics and compounds used to treat Parkinson’s disease have the most potential to impair driving.
• If an individual is aware of the impairing effects of their medication, it is possible that they may attempt to compensate by putting more effort into the driving task or by controlling task difficulty by moderating their speed.
• Dissociation between an individual’s perception of their driving ability and that observed objectively occurs with several drug classes, but is particularly apparent for compounds that modify mood.
• The effect of any given medication on driving is dependent on a large number of factors, in addition to the activity of the drug on the central nervous system (CNS). These include the age and gender of the individual; driving ability; the extent to which prescription guidelines are followed; general health and the effect of the underlying condition on driving; the dose; and the time of administration
relative to when driving occurs.
• It is possible to select drugs from certain classes that are free from impairing effects or have the least potential for impairment when used as directed, for example hypnotics, antihistamines and antidepressants. However, this is not the overriding concern when determining treatment guidelines.