Cross-Sectional Iloperidone IVGTT

Inclusion Criteria: 1. Male/Female ages 18-65 years 2. Capacity to provide informed consent 3. BMI between 20 and 30 kg/m² 4. Diagnosis of a serious mental illness, including schizophrenia, any subtype; schizoaffective disorder, any subtype; major depressive disorder, bipolar disorder, psychosis NOS, delusional disorder and paranoid disorder 5. Treatment with iloperidone, risperidone, or olanzapine for at least 6 months 6. Stable dose of antipsychotic agent for at least one month 7. Well established compliance with out-patient medications and clinically stable 8. Female subjects will be eligible to participate in the study if they are of non-childbearing potential or of child-bearing potential and willing to practice appropriate birth control methods (complete abstinence from sexual intercourse, female sterilization, sterilization of male partner, implants of levonorgestrel, injectable progestogen, oral contraceptives, intrauterine devices, or double barrier methods of contraception using spermicide with either a condom or diaphragm) during the study. Exclusion Criteria: 1. Inability to provide informed consent 2. Current substance abuse 3. Psychiatrically unstable and/or hospitalized in the past month 4. History of significant and untreated medical illness including severe cardiovascular, hepatic, renal, or untreated thyroid disease; hepatitis; or HIV 5. Current insulin treatment for diabetes 6. Currently taking the following medications: birth control pills containing norgestrol, steroids, thiazide diuretics, or treatment with agents that induce weight loss 7. Intentions of donating blood during or within 30 days of completion of the study. 8. Use of valproate or carbamazepine within four weeks of the study 9. History of immunosuppression 10. Current or recent radiation or chemotherapy treatment for cancer 11. Pregnancy or breastfeeding