MK-8189 Safety and Tolerability in Participants With Alzheimer's Disease With or Without Symptoms of Agitation-Aggression and/or Psychosis (MK-8189-017)

The main inclusion and exclusion criteria include but are not limited to the following: Inclusion Criteria: * Has a documented diagnosis of probable Alzheimer Disease based on National Institute on Aging-Alzheimer Association criteria for AD, with a history of cognitive and functional decline with gradual onset and slow progression for at least 1 year before screening, that is either corroborated by an informant who knows the participant well or is documented in medical records * Lives in the community setting with a reliable trial partner/caregiver or lives alone in an assisted living facility, with supervision and has a reliable trial partner/caregiver * Has a reliable and competent trial partner/caregiver who must have a close relationship with the participant and is knowledgeable of the participant's condition and progress and able to read, understand and speak the designated language at the study site * Can read at the 6th grade level/equivalent as determined by the investigator * Has an academic and/or employment history sufficient to exclude intellectual disability and is able, in the opinion of the investigator, to fully participate in the study * Participants receiving treatment with a cholinesterase inhibitor or other treatment for AD, must have been on a stable regimen for 3 months prior to screening and there are no expected changes in co-medication during the study * Is able to discontinue any antipsychotic medication they are taking at the time of Screening * Has a body mass index (BMI) \> 18 and ≤ 35kg/m2, inclusive Exclusion Criteria: * Has agitation/aggression or psychosis that is attributable to concomitant medications, environmental conditions, substance abuse, or an active medical or psychiatric condition * Has a known history of stroke or evidence from prior magnetic resonance imaging (MRI) scan (if available) that is clinically important in the investigator's opinion * Has evidence of a clinically relevant neurological disorder other than the disease being studied (i.e., probable AD) at Screening * Has a history of seizures or epilepsy within the last 5 years before Screening * Has evidence of a clinically relevant or unstable psychiatric disorder * Is at imminent risk of self-harm * Has a history of alcoholism or drug dependency/abuse within the last 5 years before Screening * Has a history of cancer (malignancy). Exceptions: (1) Adequately treated non-melanomatous skin carcinoma or carcinoma in situ of the cervix or; (2) Other malignancies that have been successfully treated with appropriate follow up and therefore unlikely to recur for the duration of the study * Has a family history of long QT syndrome * Previously developed severe extrapyramidal symptoms (EPS) following administration of any prescribed medication or study treatment * Is positive for hepatitis B surface antigen (HBsAg), hepatitis C antibodies or human immunodeficiency virus (HIV) * Had major surgery, donated or lost 1 unit of blood (approximately 500 mL) within 4 weeks prior to the pre-study (screening) visit * Consumes greater than 3 glasses of alcoholic beverages per day * Consumes excessive amounts, defined as greater than 6 servings (1 serving is approximately equivalent to 120 mg of caffeine) of coffee, tea, cola, energy drinks, or other caffeinated beverages per day * Is a regular user of cannabis, any illicit drugs or has a history of drug (including alcohol) abuse within approximately 3 years