A key strength of our study was its use of a case-crossover approach to harness within-person variation (i.e., individuals serving as their own controls) and estimate the degree to which poisonings were reduced on days when participants were taking benzodiazepines, as opposed to non-treatment days. Because each participant acted as his or her own control, we reduced selection and sampling bias resulting from recruitment of different cases and controls in conventional observational study design. This also allows us to study the relationship between common exposures and less common acute outcomes such as overdoses.(18, 38, 39)This strategy also enables us to examine subtle changes in exposure (i.e., variation by benzodiazepine dose, subtype) that may result in poisoning.(18) We furthermore used SSRIs as an active comparator to control for unobserved confounders and serve as a proxy for underlying conditions leading to benzodiazepine prescriptions, given their overlapping indications with benzodiazepines and no known association with drug-related poisoning or mortality in adults. The lack of association between SSRI prescriptions and poisoning is notable, suggesting that increased odds of poisoning following receipt of benzodiazepine is
