Purpose: Contradictory results were published from two studies in the late 1990s about the effects of long half-life benzodiazepine use on the risk of motor vehicle crashes (MVCs) in the elderly. The use of different study designs could explain the differences observed in these studies.
Methods: The results of an unmatched case-control study were compared to those of a case-crossover study using the same prescription claims database to determine whether the current use of benzodiazepines increased the risk of MVCs.
Results: There were 5579 cases and 12 911 controls identified between the years 1990 and 1993 in the province of Quebec, Canada. The case-control approach demonstrated an increased rate of injurious MVC associated with the current use of long-acting benzodiazepines [odds ratio (OR) 1.45; 95% confidence interval (CI): 1.12-1.88]. The case-crossover approach applied to all cases did not show any association [OR 0.99; 95%CI: 0.83-1.19]. However, among the cases restricted to subjects with four or less prescriptions filled in the previous year, corresponding more to transient exposures, the OR was elevated [OR 1.53; 95%CI: 1.08-2.16].
Conclusions: Differences in study design and analysis may explain some of the discrepancies in previous results. Both study designs provide evidence that long-acting benzodiazepines appear to be associated with an increased risk of MVC.