Emergency Department Visits Involving Hallucinogen Use and Risk of Schizophrenia Spectrum Disorder

ImportanceInterest in and use of hallucinogens has been increasing rapidly. While a frequently raised concern is that hallucinogens may be associated with an increased risk of psychosis, there are limited data on this association.ObjectivesTo examine whether individuals with an emergency department (ED) visit involving hallucinogen use have an increased risk of developing a schizophrenia spectrum disorder (SSD).Design, Settings, and ParticipantsThis population-based, retrospective cohort study (January 2008 to December 2021) included all individuals aged 14 to 65 years in Ontario, Canada, with no history of psychosis (SSD or substance induced). Data were analyzed from May to August 2024.ExposureAn incident ED visit involving hallucinogen use.Main Outcomes and MeasuresDiagnosis of SSD using a medical record–validated algorithm. Associations between ED visits involving hallucinogens and SSD were estimated using cause-specific adjusted hazard models. Individuals with an incident ED visit involving hallucinogens were compared with members of the general population (primary analysis) or individuals with ED visits involving alcohol or cannabis (secondary analysis).ResultsThe study included 9 244 292 individuals (mean [SD] age, 40.4 [14.7] years; 50.2% female) without a history of psychosis, with a median follow-up of 5.1 years (IQR, 2.3-8.6 years); 5217 (0.1%) had an incident ED visit involving hallucinogen use. Annual rates of incident ED visits involving hallucinogens were stable between 2008 and 2012 and then increased by 86.4% between 2013 and 2021 (3.4 vs 6.4 per 100 000 individuals). Individuals with ED visits involving hallucinogens had a greater risk of being diagnosed with an SSD within 3 years compared with the general population (age- and sex-adjusted hazard ratio [HR], 21.32 [95% CI, 18.58-24.47]; absolute proportion with SSD at 3 years, 208 of 5217 with hallucinogen use [3.99%] vs 13 639 of 9 239 075 in the general population [0.15%]). After adjustment for comorbid substance use and mental health conditions, individuals with hallucinogen ED visits had a greater risk of SSD compared with the general population (HR, 3.53; 95% CI, 3.05-4.09). Emergency department visits involving hallucinogens were associated with an increased risk of SSD within 3 years compared with ED visits involving alcohol (HR, 4.66; 95% CI, 3.82-5.68) and cannabis (HR, 1.47; 95% CI, 1.21-1.80) in the fully adjusted model.Conclusions and RelevanceIn this cohort study, individuals with an ED visit involving hallucinogen use had a greater risk of developing an SSD compared with both the general population and with individuals with ED visits for other types of substances. These findings have important clinical and policy implications given the increasing use of hallucinogens and associated ED visits.