Risk of schizophrenia among people with obsessive-compulsive disorder: A nationwide population-based cohort study.

High comorbidity of obsessive-compulsive disorder (OCD) has been reported in patients with schizophrenia. The sequence of OCD and schizophrenia onset might clarify the underlying pathophysiological relationships between these two disorders, but available evidence is limited. In this study, we used a population-based cohort to investigate the risk of schizophrenia in people with newly diagnosed OCD. Patients who were first diagnosed with OCD from 2000 to 2013 were selected from the Longitudinal Health Insurance Research Database. The non-OCD group was randomly sampled, and matched with the OCD group by gender, age, urbanization level, and income. Cox regression analyses and competing risk model were used to estimate the risk of schizophrenia, adjusting for potential confounding factors. In total, 2009 patients with OCD and 8036 controls were identified. The crude incidences of schizophrenia in the OCD and non-OCD groups were 876.2 per 100,000 person-years and 28.7 per 100,000 person-years, respectively. After adjustment, a substantially higher risk of schizophrenia was observed in the OCD group (hazard ratio = 30.29, 95% confidence interval = 17.91-51.21). Male gender, age of OCD onset before 20 years, and antipsychotic prescription were associated with schizophrenia. Patients with comorbidity of autistic disorder have higher risk of schizophrenia (hazard ratio = 4.63, 95% confidence interval = 1.58-13.56). In conclusion, OCD diagnosis, male gender, age of OCD onset before 20 years, comorbidity of autistic disorder, and antipsychotic use were associated with higher risk of schizophrenia. It is essential for psychiatrists to note that OCD may be the initial presentation of schizophrenia.