Pre-admission prescription of selective serotonin reuptake inhibitors and mortality in critical illness: a national cohort study from 2020 to 2023.

Background: We aimed to determine whether selective serotonin reuptake inhibitor (SSRI) prescription within 30 days before intensive care unit (ICU) admission was associated with 30-day and 90-day mortality in critically ill adults, and to evaluate effect modification by underlying psychiatric disorders. Methods: We conducted a nationwide retrospective cohort study of adults with a first ICU admission in South Korea from 2020 through 2023. Pre-admission SSRI prescription was defined using prescription supply records during the 30 days before ICU admission. Propensity score matching and Cox proportional hazards models were used to evaluate 30-day and 90-day mortality. Results: Pre-admission SSRI prescription was associated with lower 30-day and 90-day mortality after propensity score matching. Similar associations were observed in the full cohort and when prescription coverage included the day immediately before ICU admission. The associations appeared stronger among patients with documented psychiatric disorders. Conclusions: Pre-admission SSRI prescription was associated with lower short- and intermediate-term mortality in critically ill adults. These observational findings do not establish a causal protective effect and should be interpreted in light of potential residual confounding. Trial registration: None.