RecruitingPhase 1Drug trialRepurposing Nucleoside Reverse Transcriptase Inhibitors for Treatment of ADThis is a randomized, double-blind clinical trial of a daily oral dose of 200 mg emtricitabine vs. placebo in 35 participants with biomarker-confirmed MCI or mild to moderate dementia due to Alzheimer's disease. Study duration for each subject participating in the placebo-controlled research study will be approximately 12 months (up to a 3 months Screening Period, Baseline visit (1 month), 6 months of placebo or emtricitabine dosing, and 1 month follow-up). Participants will have up to 2 months to complete all procedures for the month 6 study visit.