The objective of the study was to study the effects of donepezil on cognition in patients with schizophrenia. The investigators conducted a 12-week, double-blind, placebo-controlled trial of donepezil as adjunctive treatment to antipsychotic drugs on patients with schizophrenia.

The investigators conducted a 12-week, double-blind, placebo-controlled trial of donepezil as adjunctive treatment to antipsychotic drugs on patients with schizophrenia.The trial will be complete in 2012.

Inclusion Criteria:

• DSM-IV diagnosis of schizophrenia as determined by the Structured Clinical Interview for DSM-IV Axis I Disorders-Clinician Version;
• Between 18 and 40 years of age;
• Duration of the illness must be longer than 2 year;
• Patient's current antipsychotic medication regimen must be stable;
• Must be in a stable living arrangement;

Exclusion Criteria:

• Patient has mental retardation or severe organic brain syndromes;
• Treatment with Electroconvulsive Therapy (ECT) within 6 months prior to screening;
• Has suicidal attempts or ideation or violent behavior within the last 12 months;
• Patient has a history of alcohol/drug dependence;