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:

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

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

4. Does not meet criteria for dementia, AND

5. Positive Screening amyloid imaging PET scan using [18F]flutametamol tracer orpositive Screening CSF tau:amyloid─β42 (Aβ42) ratio (Participants with a priorpositive amyloid imaging PET scan or a Screening PET scan with florbetaben orflorbetapir may be enrolled without a Screening flutemetamol scan with Sponsorapproval)

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

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

8. Must have a reliable and competent trial partner/informant who has a closerelationship with the participant and is willing to accompany the participant to allrequired trial visits, and to monitor compliance of the administration of the trialmedication Inclusion Criteria for Extension Period (Part 2):

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

10. Participant must have a reliable and competent trial partner who must have a closerelationship with the subject

Exclusion Criteria:

1. History of stroke

2. Evidence of a clinically relevant neurological disorder other than the disease beingstudied (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 majordepression 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 beforeScreening

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

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

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

10. History of malignancy occurring within the 5 years before Screening, except foradequately 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 beforeScreening

12. Use of any investigational drugs or participation in clinical trials within the 30days 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 includingbut not limited to claustrophobia, excessive weight or girth

16. History or current evidence of long QT syndrome, corrected QT (QTc) interval ≥470milliseconds (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 thepersonnel of the investigational or sponsor staff directly involved with this trial Exclusion Criteria for Extension Period (Part 2):

18. Participant is at imminent risk of self─harm or of harm to others

19. Has developed a recent or ongoing, uncontrolled, clinically significant medical orpsychiatric condition

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

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

22. 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):

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