We used a case-crossover study design that exploited within-subject variation in exposure and outcome; this addresses unobserved, time-invariant confounding by allowing each individual to serve as their own control. Units of observation were person-days, denoting days during which participants were enrolled in insurance. Case periods were days when a participant experienced non-fatal drug-related poisonings. Control periods were nearby days without poisoning events.(24, 25) We characterized each person-day of observation by: (1) presence or absence of benzodiazepine treatment; (2) presence or absence of buprenorphine treatment. We permitted each participant to have multiple poisoning events as long as these fell within the interval of at most 365 days before and after index poisoning (Figure 2).Individuals with fewer observation days on either side of the index event were included with missing days treated as censored. We evaluated participants during the year prior to and after a patient’s first drug-related poisoning (index date), thus limiting participants to two-year periods of observation to reduce heterogeneity in observation time per person. We included periods both before and after the index poisoning so as to define the
