Hypertension has become recognized over the last 20 years as a potent risk factor not only for heart attacks and stroke, but also for Alzheimer's disease (AD) and overall brain health. Uncontrolled hypertension in midlife has been shown to be associated with Alzheimer pathology in the brain up to 36 years later. Two drug classes that have been used to treat hypertension include the so-called "angiotensin converting enzyme inhibitors" (ACEIs) and "angiotensin receptor blockers" (ARBs). A strong rationale for comparing these two drug classes has emerged, insofar as ARBs have been demonstrated both to improve cognition and to interfere with pathological processes involved in the development of AD, both features that are not associated with ACEIs. Yet, studies designed to be informative in patient populations have not been performed to compare these two anti-hypertensive drug classes directly. Here, we plan to conduct a clinical study to do just that, using brain imaging measurements to demonstrate in a comparative manner the effect of ACEIs vs. ARBs in a "face-off" against brain degeneration (which is associated with the development of AD) in people who are at risk for developing AD and who are already taking medications to control blood pressure. In addition, we will conduct analyses of the relative impact of these two classes of medications on cognition and quality of life over a one-year period. This study will be exploratory in terms of outcomes, requiring larger and longer studies to confirm the results. If positive, this study could lead to practice-changing implications, especially for hypertension control in AD subjects. It would also repurpose a well-known class of drugs in wide use for hypertension and coronary artery disease.