MK-8189 Multiple Dose Study in Healthy Volunteers and Schizophrenia Patients (MK-8189-003)

Inclusion Criteria:

INCLUSION CRITERIA FOR SCHIZOPHRENIA PARTICIPANTS

- Male or non-pregnant and non-breast feeding female. If participant is male with a
female partner of child-bearing potential, participant must agree to use a medically
acceptable method of contraception during the trial and for 120 days after the last
dose of trial drug. If their partner is pregnant, males must agree to use a condom

- Body Mass Index (BMI) ≥ 18.5 and ≤ 40 kg/m^2

- Meet diagnostic criteria for schizophrenia or schizoaffective disorder according to
the Diagnostic and Statistical Manual of Mental Disorders (DSM) criteria with the
onset of the first episode being no less than 2 years prior to study entry

- Be in the non-acute phase of illness and clinically stable for 3 months prior to
screening

- History of receiving and tolerating antipsychotic medication within the usual dose
range employed for schizophrenia

- Participants with hypothyroidism, diabetes, high blood pressure, chronic respiratory
conditions or other mild forms of these medical conditions could be considered as
candidates for study enrollment if their condition is stable and the prescribed dose
and regimen of medication is stable for at least 3 months prior to screening and
there are no expected changes in comedication during the study

- Has a negative urinary drug screen at screening

INCLUSION CRITERIA FOR HEALTHY PARTICIPANTS

- Male, or non-pregnant and non-breast feeding female of Japanese or non-Japanese
descent. If participant is male with a female partner of child-bearing potential,
participant must agree to use a medically acceptable method of contraception during
the trial and for 120 days after the last dose of trial drug. If their partner is
pregnant, males must agree to use a condom

- Body Mass Index (BMI) ≥ 18.5 and ≤ 35 kg/m^2

- In good health

- Nonsmoker and/or has not used nicotine or nicotine-containing products (e.g.,
nicotine patch) for at least approximately 3 months

- Has a negative urinary drug screen at screening

Exclusion Criteria:

EXCLUSION CRITERIA FOR SCHIZOPHRENIA PARTICIPANTS

- DSM-IV axis I psychiatric diagnosis other than schizophrenia or schizoaffective
disorder within one month of screening

- Has evidence or history of mental retardation, borderline personality disorder,
anxiety disorder, or organic brain syndrome

- History of neuroleptic malignant syndrome or moderate to severe tardive dyskinesia

- Untreated or uncompensated clinically significant renal, endocrine, hepatic,
respiratory, gastrointestinal, psychiatric, neurologic, cardiovascular,
hematological, immunological or cerebrovascular disease, malignance, allergic disease
or other chronic and/or degenerative process at screening

- Has a history of cancer (malignancy) with certain exceptions

- Treatment with clozapine for schizophrenia or treatment with monoamine oxidase
inhibitors within 3 months of screening

- Received a parenteral depot antipsychotic medication within 3 months of screening

- Participated in another investigational study within 4 weeks, prior to screening

EXCLUSION CRITERIA FOR HEALTHY PARTICIPANTS

- History of clinically significant endocrine, gastrointestinal, cardiovascular
(including hypertension, angina, coronary artery disease, valvular disease, heart
rate or rhythm abnormalities), hematological, hepatic, immunological, renal,
respiratory, genitourinary or major neurological (including stroke and chronic
seizures) abnormalities or diseases

- Mentally or legally incapacitated

- History of clinically diagnosed depression, anxiety disorder, or any history of
psychiatric disorders having required drug treatment or hospitalization

- History of cancer (malignancy)

- Unable to refrain from or anticipates the use of any medication, including
prescription and non-prescription drugs or herbal remedies throughout the trial

- Participated in another investigational study within 4 weeks, prior to screening