The objective of this study is to evaluate the effectiveness of a marketed drug in the treatment of schizophrenia, as an add-on therapy to antipsychotics over a 12-week period. Subjects with schizophrenia who have been maintained on a stable dose of antipsychotics and who fulfill the screening entrance criteria will have an assessment 1-7 days after the first visit to confirm eligibility.

Inclusion criteria:

• If female, must not be pregnant, or must be incapable of conceiving or be taking steps to prevent conception.
• Diagnosis of Schizophrenia
• Patients must be taking clozapine monotherapy or other atypical antipsychotic at least 3 months prior to this study.

Exclusion criteria:

• Patients who are currently taking or have taken antidepressant medication in the last month prior.
• Patients who are or have been suicidal or homicidal in the last 6 months.
• Patients with a history of autistic disorder or another pervasive developmental disorder
• Patients whose condition is due to the direct physiological effects of a substance (e.g. a drug of abuse, a medication) or a general medical condition

Patient-level data for this study will be made available through www.clinicalstudydatarequest.com following the timelines and process described on this site.