Incidence, prevalence and determinants of substance-induced mental disorders in British Columbia, 2022-2023: a population-based study.

aimsSubstance-induced mental disorders (SIMD) are an under-recognized consequence of psychoactive substance use, despite major implications for treatment needs, health service demand and outcomes. In the context of British Columbia's (BC's) ongoing toxic drug emergency, we aimed to (1) estimate the incidence and prevalence of SIMD in the provincial population and (2) describe socio-demographic, geographic, clinical and substance-specific patterns over a two-year period.

methodsWe conducted a retrospective, population-based study using linked administrative health data from Population Data BC for residents aged ≥12 years between 1 January 2022 and 31 December 2023. SIMD cases were identified using a novel algorithm combining diagnostic codes with temporal linkage between substance-related events (poisoning, withdrawal or substance use disorder) and subsequent psychiatric diagnoses. Incident cases had no record of the same mental disorder in the previous two years; prevalent cases met SIMD criteria at any point in the study period. We calculated monthly, annual and cumulative incidence and prevalence rates per 10,000 population, stratified by sex, age group, health authority, urban/rural residence, neighbourhood income, psychiatric diagnosis, substance class, concurrent substance use disorder, involuntary treatment and mortality.

resultsWe identified 37,474 incident and 83,307 prevalent SIMD cases over two years, corresponding to a cumulative incidence of 77.5 and prevalence of 171.4 per 10,000 population. Monthly rates fluctuated in 2022, followed by a rise through 2023, with highest incidence (35.2 per 10,000) and prevalence (328.3 per 10,000) in May 2023. Males accounted for 62% of incident and 59% of prevalent cases; mean age was 43 years, with highest proportions in the 25-44 age range. Northern and Vancouver Island Health Authorities had the greatest burden. On average, individuals with SIMD had 3.2-3.6 healthcare visits per month. Cannabis- and hallucinogen-induced disorders were concentrated among younger people, while alcohol- and tobacco-related SIMD predominated in older adults; stimulant-related SIMD showed the highest hospitalization and involuntary treatment rates. Only about one-third of prevalent and fewer than one in five incident cases had a recorded concurrent substance use disorder.

conclusionsSIMDs are common, clinically complex and unevenly distributed across demographic and geographic groups in BC. The high rates, substantial service use and frequent occurrence outside documented substance use disorder diagnoses underscore the need for improved detection of SIMD, integration of psychiatric and addiction care and regionally tailored prevention and treatment strategies within the ongoing toxic drug emergency.