Exploring dual diagnosis in opioid agonist treatment patients: A registry-linkage study in Czechia and Norway

Abstract

Background: Knowledge on co-occurring mental disorders (termed ‘dual diagnosis’) among patients receiving opioid agonist treatment (OAT) is scarce. This study aimed (1) to estimate the prevalence and structure of dual diagnoses in two national cohorts of OAT patients and (2) to compare mental disorders between OAT patients and the general populations standardized by age and sex. Methods: A registry-linkage study of OAT patients from Czechia (N = 4,280) and Norway (N = 11,389) during 2010–2019 was conducted. Data on mental disorders (F00-F99; ICD-10) recorded in nationwide health registers were linked to the individuals registered in OAT. Sex-specific age-standardized morbidity ratios (SMR) were calculated for 2019 to compare OAT patients and the general populations. Results: In addition to opioid use disorder (OUD), other substance use disorders (SUDs) were frequently recorded in both countries. The prevalence of dual diagnosis was 57.3% for Czechia and 78.3% for Norway. Anxiety, personality disorders, and depression were the most frequent. The largest country-specific differences were observed for ADHD (0.5% in Czechia, 15.8% in Norway). OAT females had a significantly higher prevalence of co-occurring mental disorders, whereas SMRs were higher in OAT males. Conclusions: Dual diagnosis in OAT patients is prevalent and requires appropriate interventions. Country-specific differences may stem from variations in diagnostics and care, reporting to registers, OAT provision, or substance use patterns.