The Temporal Relationship between Selected Mental Disorders and Substance-Related Disorders: A Nationwide Population-Based Cohort Study

Introduction. Previous studies have examined the association between specific mental disorders, particularly mood and anxiety disorders, and substance-related disorders; but the temporal link between them remains unclear. This study aimed to examine whether individuals with specific mental disorders, including affective psychoses, neurotic disorders, schizophrenia, personality disorders, and adjustment reaction, have higher risks for subsequently developing substance-related disorders compared to those without. Methods. A large-scale study with longitudinal data was conducted using the Taiwan National Health Insurance Research Database (NHIRD) consisting of 2,000,118 patients' medical records from 2000 to 2009. A total of 124,423 people diagnosed with selected mental disorders and the same number of people without the diagnoses of the selected disorders were identified between January 1, 2001, and December 31, 2006, and followed up for the diagnoses of substance-related disorders till the end of 2009. We estimated the risk for subsequently developing substance-related disorders among patients with the selected mental disorders compared to those without by using Cox proportional hazard models. The cumulative incidence of substance-related disorders was calculated using the Kaplan-Meier method. Results. The risk for developing substance-related disorders in patients with selected mental disorders is about 5 times (HR=5.09, 95% CI: 4.74-5.48) higher than those without after adjusting for potential confounding variables. From the multivariate analyses of subsamples stratified by age, sex, and urban and income levels, we found all adjusted hazard ratios were significantly higher than 1.0, ranging from 2.12 (95% CI: 1.72-2.62) to 14.55 (95% CI: 7.89-26.83). For children and adolescents aged 10-19 years, those with specific mental disorders had 14.55-fold higher risk for developing substance-related disorders in later life compared to their counterparts. Furthermore, patients with personality disorders had the highest risk (HR=25.05). Conclusions. The earlier onset of the selected mental disorders is a potential risk for developing substance-related disorders in later life, particularly for personality disorders. Health professionals should pay more attention to this at-risk population, especially to adolescents with mental disorders.