A Clinical Study to Investigate the Effect of an Investigational Drug as an Added Medication to an Antipsychotic, in Adults With Schizophrenia, as Measured Positron Emission Tomography (PET) Imaging

Inclusion Criteria

-1. Subject must give written informed consent and privacy authorization prior to participation in the study.

• Subject must be willing and able to comply with the study procedures and visit schedule, including required minimum week in-clinic treatment period, and must be able to understand and follow verbal and written instructions
• Male or female subject between 18 to 45 years of age (inclusive) at the time of consent
• Subject meets Diagnostic and Statistical Manual of Mental Disorders (DSM-5) criteria for a primary diagnosis of schizophrenia as established by clinical interview (using the DSM-5 as a reference and confirmed using the Structured Clinical Interview for DSM-V Clinical Trials Version [SCID-CT]). The duration of the subject's illness whether treated or untreated must be ≥ 6 months.
• Subject must be on a stable dose of a single antipsychotic medication, dosed within the labeled dose-range, for a minimum of 3 weeks prior to the PET scan at the screening visit. Patients taking clozapine are not eligible to participate
• Subject must have a Clinical Global Impression-Severity (CGI-S) score ≥ 3 (mild or greater)
• Subject must have a Positive and Negative Syndrome Scale (PANSS) total score ≥ 70.
• . Subject's BMI must be at least 18 kg/m2 but no more than 35 kg/m2.
• Female subjects must have a negative serum pregnancy test at screening; as well as a negative urine pregnancy test prior to the PET scan on each day PET scans are performed, as well as prior to the MRI scan.
• Female subject of childbearing potential and male subject with female partner of childbearing potential must agree to use an acceptable form of birth control from at least 30 days prior to administration of the first dose of study drug, during the treatment period, and 60 days after completion or premature discontinuation from the study drug. Male subjects must also refrain from semen/sperm donation 30 days prior to administration of the first dose of study drug, during the treatment period, and 60 days after completion or premature discontinuation from the study drug.
• Adequate contraception is defined as continuous use of either two barrier methods (eg, condom and spermicide or diaphragm with spermicide) or a hormonal contraceptive. Acceptable hormonal contraceptives include the following: a) contraceptive implant (such as Norplant®) implanted at least 90 days prior to screening; b) injectable contraception (such as meroxyprogesterone acetate injection) given at least 14 days prior to screening; or c) oral contraception taken as directed for at least 30 days prior to screening. In the Investigator's judgment, the subject will adhere to this requirement.
• . Female subjects who are of non-childbearing potential are not required to abide by birth control requirements.
• Non-childbearing potential is defined as subject who is surgically sterile, has undergone tubal ligation, or is postmenopausal (defined as at least 12 months of spontaneous amenorrhea or between 6 and 12 months of spontaneous amenorrhea with follicle stimulating hormone [FSH] concentrations within postmenopausal range as determined by laboratory analysis).
• Subject is, in the opinion of the Investigator, generally healthy based on screening medical history, PE, neurological examination, vital signs, clinical laboratory values (hematology, serum chemistry urinalysis, lipid panel, coagulation panel, thyroid panel, and serum prolactin).
• Subject has had a stable living arrangement at the time of screening and agrees to return to a similar living arrangement after discharge. This criterion is not meant to exclude subjects who have temporarily left a stable living arrangement (eg, due to psychosis). Such subjects remain eligible to participate in this study. Chronically homeless subjects should not be enrolled.
• Subject must agree to comply with all medication restrictions for the required length of time.

Exclusion criteria

• 1. Subject answers "yes"