Elevated psychiatric and substance use disorders in people with intellectual disabilities in a Swedish National...

Adults with intellectual disability (ID) experience marked mental health inequities, yet population-wide estimates that capture both primary- and specialist-care diagnoses remain scarce.

Using nationwide Swedish registries, including primary care, specialist, inpatient, prescription drug, criminal, and suspicion registers, we included all individuals born in Sweden between 1958 and 1997 (N = 3,970,600), including 38,818 individuals with ID diagnoses (0.98%; 49.1% mild, 13.3% moderate, and 9.6% severe/profound). Hazard ratios (HR) were calculated using Cox proportional hazards regression to estimate the relative risk of lifetime diagnoses of major depression, anxiety disorders (ANX), obsessive-compulsive disorder (OCD), bipolar disorder (BD), attention-deficit/hyperactivity disorder (ADHD), drug use disorder, alcohol use disorder, schizophrenia, and other nonaffective psychosis. Additionally, cohort effects on psychiatric diagnosis risks in adults with intellectual disabilities versus the general population were evaluated.

People with ID were at higher risk for all psychiatric and substance use disorders, with HRs ranging from 1.7-2.0 for major depression and anxiety, drug and alcohol use disorders, 3.5-5.8 for BD, OCD and ADHD, and 10.9-12.7 for schizophrenia and other nonaffective psychosis. Higher prevalence was consistently seen among those with mild versus moderate or severe/profound intellectual disability. Relative risks narrowed modestly in successive birth cohorts, although absolute differences remained substantial.

Across six decades of follow-up, adults with ID faced markedly higher psychiatric and substance-use morbidity - most pronounced for psychotic disorders - than the general population. Whole-system mental-health screening and tailored interventions are required to address this persistent disparity.