• Fasting lipids, including triglycerides and total cholesterol [ Time Frame: Measured at Week 12 ] [ Designated as safety issue: Yes ]
  
• Weight [ Time Frame: Measured at Week 12 ] [ Designated as safety issue: Yes ]
  
• Body Mass Index (BMI) [ Time Frame: Measured at Week 12 ] [ Designated as safety issue: Yes ]
  
• Insulin resistance and glucose metabolism [ Time Frame: Measured at Week 12 ] [ Designated as safety issue: Yes ]
  

• Food intake [ Time Frame: Measured at Week 12 ] [ Designated as safety issue: Yes ]
  
• Energy expenditure [ Time Frame: Measured at Week 12 ] [ Designated as safety issue: Yes ]
  
• Systematic Assessment for Treatment Emergent Effects (SAFTEE) [ Time Frame: Measured at Week 12 ] [ Designated as safety issue: Yes ]
  
• Vital signs [ Time Frame: Measured at Week 12 ] [ Designated as safety issue: Yes ]
  
• Plasminogen activator molecule-1 (PAI-1) [ Time Frame: Measured at Week 12 ] [ Designated as safety issue: Yes ]
  
• LDL particle size [ Time Frame: Measured at Week 12 ] [ Designated as safety issue: Yes ]
  
• C-reactive protein [ Time Frame: Measured at Week 12 ] [ Designated as safety issue: Yes ]
  
• Soluble intercellular adhesion molecule-1 [ Time Frame: Measured at Week 12 ] [ Designated as safety issue: Yes ]
  
• Lipid abnormalities [ Time Frame: Measured at Week 12 ] [ Designated as safety issue: Yes ]
  

Schizophrenia is a severely disabling brain disorder. People with schizophrenia often experience hallucinations and delusions, as well as overall difficulty with everyday functioning. Although the medications available to treat the disorder are generally effective, many cause undesirable side effects. Clozapine, for example, is a strong tranquilizer that functions like an antipsychotic medication. It has been shown to be effective in reducing the symptoms of schizophrenia, but can bring about serious side effects, including heart failure, weight gain, and diabetes. Aripiprazole, an atypical antipsychotic medication, has been shown to have fewer side effects than older antipsychotic drugs. The addition of aripiprazole to a clozapine treatment regimen may reduce the negative side effects of clozapine. This study will evaluate the effects of combination treatment with aripiprazole and clozapine on insulin resistance, blood fat levels, and weight gain in people with schizophrenia.

Individuals interested in participating in this 12-week, double-blind study will first attend a screening session at the study site. Medical and psychiatric evaluations will be completed, blood samples will be taken, and an EKG will be performed. Eligible participants will undergo baseline assessments and then be randomly assigned to receive either aripiprazole or placebo in addition to their prescribed dose of clozapine. Participants will take one 15-mg capsule of their assigned medication once a day for 8 weeks. Study visits will occur biweekly for the first 8 weeks, followed by one final visit at Week 12. At each study visit, medication will be distributed, and the following criteria will be assessed: vital signs; weight; complete blood count; medication side effects; and extrapyramidal symptoms (EPS), which are potential neurological side effects of antipsychotic medications and may include involuntary movements, tremors, and rigidity. The Week 12 follow-up visit will include an EKG, and assessments of the following criteria: vital signs; medication side effects; treatment efficacy; blood counts; weight and height; and waist and hip circumference. At baseline and Week 12, participants will also undergo a frequently sampled intravenous glucose tolerance test (FSIVGTT). This involves intravenous infusion of glucose followed by frequent blood sampling to measure insulin and glucose concentrations. During the 4 days prior to each FSIVGTT, participants will record their food intake and wear an activity monitor.