Elpipodect (MK-8189) Multiple Dose Study in Healthy Volunteers and Schizophrenia Participants (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 pa…