OBJECTIVE

To compare the prevalence of obsessive-compulsive symptoms (OCS) in a population of patients with schizophrenia taking clozapine, olanzapine, or risperidone or taking no antipsychotic medication.

METHOD

Baseline data of the Genetic Risk and Outcome of Psychosis study were collected between April 2005 and October 2008. We conducted a naturalistic cross-sectional study of 543 patients with schizophrenia and related disorders, who were recruited from multiple mental health centers, including inpatient and outpatient clinics, across The Netherlands. The patients met Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria and were taking no antipsychotic medication or taking clozapine, olanzapine, or risperidone. OCS severity was measured with the Yale-Brown Obsessive Compulsive Scale. We compared patients to a sample of 575 healthy controls.

RESULTS

Prevalence of OCS in patients was significantly higher than in the control sample, 23.4% versus 4.9% (χ(2) = 73.8, P < .001). Patients taking clozapine reported OCS significantly more often during the last week (38.9%), when compared to patients taking olanzapine (20.1%, χ(2) = 10.02, P = .002) or risperidone (23.2%, χ(2) = 5.96, P = .015) and patients taking no antipsychotics (19.6%, χ(2) = 8.20, P = .004). Patients taking clozapine for 6 months or longer reported OCS significantly more often than patients taking clozapine for less than 6 months, 47.3% versus 11.8% (χ(2) = 6.89, P = .009).

CONCLUSIONS

Treatment with clozapine in patients with schizophrenia is associated with a higher prevalence of OCS, especially when patients have been taking clozapine for 6 months or longer. We cannot rule out the possibility that this association is related to illness characteristics. Patients treated with risperidone or olanzapine or without treatment with antipsychotic medication had comparable prevalence of OCS, all significantly higher than the control sample.