As shown in Figure 2, our primary outcome was non-fatal drug-related poisonings (including overdoses). Controls were adjacent person-days when poisoning event did not occur. Poisonings were defined using International Classification of Disease codes and Healthcare Common Procedure Coding System codes for naloxone reversal. Per guidelines compiled by Center for Disease Control consensus recommendations for poisoning surveillance,(28) our codes encompassed not only opioids but also alcohol, benzodiazepines, psychotropic medication, and overdose with other substances (eTable 1). This was intended to capture conditions commonly associated with chronic drug misuse, as well as avoid misclassification bias and underestimation of overdose risks. We searched all emergency room visits, outpatient ambulatory visits, and hospitalizations for relevant diagnostic codes.(28)
