Clozapine has superior efficacy in treatment-resistant schizophrenia, and has various effects on psychiatric comorbidities, which may affect the illness course.

We aimed to assess the past and current psychiatric comorbidities in schizophrenia patients treated with clozapine, and study their relationship with clinical variables.

Consecutive 122 outpatients who met DSM-IV criteria for schizophrenia receiving clozapine were included. Information about past and current clinical status were gathered through a clinical interview and review of the medical records, along with laboratory test results. Patients were assessed with structured clinical interview for Axis-I Disorders for DSM-IV, Clinical Global Impression Scale, Positive and Negative Syndrome Scale (PANSS), Calgary Depression Scale, Yale-Brown Obsessive Compulsive Scale (Y-BOCS), Panic and Agoraphobia Scale (PAS), WHO-Disability Assessment Schedule-II.

There was a significant decrease in the diagnosis of depression, alcohol and substance use disorder, number of suicide attempts, and an increase in the diagnosis of obsessive compulsive disorder (OCD) after clozapine initiation. Clozapine related de novo OCD appeared in 48.4% of the patients, and there was a positive correlation between Y-BOCS total scores and clozapine dose and plasma levels. In the de novo OCD group, compulsion scores were higher than obsession scores with checking most prevalent among compulsions. Total PANSS, Y-BOCS, PASscores were positively correlated withtotal disability score.

Clozapine seems to decrease comorbid depression, alcohol and substance use and number of suicide attempts and increase OCD. Assessment and treatment of psychiatric comorbidities in clozapine using schizophrenia patients is vital to decrease disability.