Efficacy and Safety Trial of Verubecestat (MK-8931) in Participants With Prodromal Alzheimer's Disease (MK-8931-019)

Inclusion Criteria:

   1. Diagnosis of prodromal AD, including the following:

      1. History of subjective memory decline with gradual onset and slow progression for
      at least one year corroborated by an informant,

      2. Objective impairment in episodic memory by memory test performed at Screening,

      3. Does not meet criteria for dementia, AND

      4. Positive Screening amyloid imaging PET scan using [18F]flutametamol tracer or
      positive Screening CSF tau:amyloid-β42 (Aβ42) ratio (Participants with a prior
      positive amyloid imaging PET scan or a Screening PET scan with florbetaben or
      florbetapir may be enrolled without a Screening flutemetamol scan with Sponsor
      approval)

   2. Able to read at a 6th grade level or equivalent

   3. If participant is receiving an acetylcholinesterase inhibitor or memantine, the dose
   must have been stable for at least three months before Screening

   4. Must have a reliable and competent trial partner/informant who has a close
   relationship with the participant and is willing to accompany the participant to all
   required trial visits, and to monitor compliance of the administration of the trial
   medication

Inclusion Criteria for Extension Period (Part 2):

   1. Tolerated study drug and completed the initial 104-week period of the trial (Part 1)

   2. Participant must have a reliable and competent trial partner who must have a close
   relationship with the subject

Exclusion Criteria:

   1. History of stroke

   2. Evidence of a clinically relevant neurological disorder other than the disease being
   studied (i.e., prodromal AD)

   3. History of seizures or epilepsy within the last 5 years

   4. Evidence of a clinically relevant or unstable psychiatric disorder, excluding major
   depression in remission

   5. Participant is at imminent risk of self-harm or of harm to others

   6. History of alcoholism or drug dependency/abuse within the last 5 years before
   Screening

   7. Participant does not have a magnetic resonance imaging (MRI) scan obtained within 12
   months of Screening and is unwilling or not eligible to undergo an MRI scan at the
   Screening Visit. With Sponsor approval, a head computed tomography (CT) scan may be
   substituted for MRI scan to evaluate eligibility

   8. History of hepatitis or liver disease that has been active within the 6 months prior
   to Screening

   9. Recent or ongoing, uncontrolled, clinically significant medical condition within 3
   months of Screening

10. History of malignancy occurring within the 5 years before Screening, except for
   adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer,
   or localized prostate carcinoma

11. Clinically significant vitamin B12 or folate deficiency in the 6 months before
   Screening

12. Use of any investigational drugs or participation in clinical trials within the 30
   days before Screening

13. History of a hypersensitivity reaction to more than three drugs

14. Has human immunodeficiency virus (HIV) by medical history

15. Participant is unwilling or has a contraindication to undergo PET scanning including
   but not limited to claustrophobia, excessive weight or girth

16. History or current evidence of long QT syndrome, corrected QT (QTc) interval ≥470
   milliseconds (for male participants) or ≥480 milliseconds (for female participants),
   or torsades de pointes

17. Close family member (including the trial partner, spouse or children) who is among the
   personnel of the investigational or sponsor staff directly involved with this trial

Exclusion Criteria for Extension Period (Part 2):

   1. Participant is at imminent risk of self-harm or of harm to others

   2. Has developed a recent or ongoing, uncontrolled, clinically significant medical or
   psychiatric condition

   3. Results of safety assessments (e.g., laboratory tests) performed in participant at end
   of Part 1 that are clinically unacceptable to the Investigator

   4. Has developed a form of dementia that is not AD

   5. Has progressed to dementia due to AD per investigator diagnosis in the initial
   104-week study (Part 1).

Exclusion Criteria for NFT PET Substudy (Part 2):

1. Had one or two PET scans with MK-6240 in the initial 104-week study.