Cognition Platform Study in Participants at Risk for Alzheimer's Disease (AD) (MK-0000-413)

• Has an Mini Mental State Examination (MMSE) score between 18 and 28 (inclusive) at Screening (Visit 1) and Baseline (Visit 2)
• Has a diagnosis of mild cognitive impairment (MCI) or mild Alzheimer's Disease (AD)
• Has an Modified Hachinski Ischemia Scale (MHIS) score of ≤4
• Must have a reliable and competent study partner/informant who accompanies participant to study visits and participates in assessments
• Be willing to provide a blood sample for Apolipoprotein E (APOE) genotyping
• Does not have intellectual disability
• Be able to speak, read, hear, and understand the language of the study staff and the Informed Consent Form (ICF)
• Be able and willing to adhere to the study visit schedule
• Have visual acuity, visual function, hearing, and gross and fine motor skills adequate to support study participation
• Be capable of performing the Cogstate battery assessments, as demonstrated at the Baseline/Familiarization Visit (Visit 2)
• A female participant is eligible to participate if she is a woman of nonchildbearing potential (WONCBP)

Exclusion Criteria:

• Is at imminent risk of self-harm
• Has evidence of a clinically relevant neurological disorder other than AD at screening, including but not limited to: Parkinson's disease, frontotemporal dementia, Huntington's disease, amyotrophic lateral sclerosis, multiple sclerosis, progressive supranuclear palsy, dementia with Lewy bodies, other types of dementia, neurosyphilis or that led to persistent cognitive deficits, or has a history of seizures or epilepsy within the last 5 years before screening
• Has a known history of stroke or has a diagnosis of vascular dementia
• Has history of multiple episodes of head trauma, or head trauma resulting in protracted loss of consciousness, or serious infectious disease affecting the brain, within the prior 3-5 years
• Has evidence of a clinically relevant or unstable psychiatric disorder, based on Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5), including schizophrenia or other psychotic disorder, bipolar disorder, major depression, or delirium
• Has a recent or ongoing, uncontrolled, clinically significant medical condition within 2 months of the Screening visit
• Has a history of cancer
• Has a relative contraindication to donepezil including sick sinus syndrome, first, second, or third-degree heart block, bradycardia, active gastrointestinal (GI) bleeding, Zollinger-Ellison syndrome, uncontrolled peptic ulcer disease, or uncontrolled asthma
• Has a history of significant multiple and/or severe allergies or has had an anaphylactic reaction or significant intolerability to prescription or non-prescription drugs or food. Exception: Participants with selected allergies may be enrolled with Sponsor's approval
• Is positive for Hepatitis B surface antigen (HBsAg), hepatitis C antibodies or human immunodeficiency virus (HIV) [participants with a history of chronic hepatitis C virus with a documented cure and/or a positive serologic test for HCV with a negative HCV viral load may be included]
• Has clinically significant vitamin B12 or folate deficiency in the 6 months immediately before screening, or vitamin B12 or folate deficiency in addition to increased serum homocysteine and methylmalonic acid levels at screening
• Has prior AD treatment
• Has participated in another investigational study within 4 weeks
• Has a known history of structural changes on screening magnetic resonance imaging (MRI) scan that are clinically important, including signs indicative of vascular dementia, large infarct, lacunes in critical areas, space-occupying lesions, or extensive white matter disease
• Is unwilling to or not eligible to undergo a MRI scan (if a prior MRI scan is not available)
• Is pregnant, is attempting to become pregnant, or is nursing children
• Has a history of alcoholism or drug dependency/abuse within the last 5 years prior to the Screening visit
• Consumes greater than 3 glasses of alcoholic beverages per day
• Consumes excessive amounts, defined as greater than 6 servings 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 abuse within approximately 5 years. A participant who is a recreational user of cannabis or other drugs within the past 2 years can be enrolled as long as recreational use does not meet the definition of drug abuse and participant agrees to refrain from substance use for duration of study participation
• Participants must have a negative urine drug screen (UDS) prior to randomization
• Had major surgery within 3 months prior to the Screening visit that would interfere in the participant's ability to fully participate in the study
• Has undergone neuropsychological testing (including the MMSE) or cognitive remediation in the past 4 weeks
• Is or has an immediate family member who is investigational site or Sponsor staff directly involved with this study