Dementia is a common and serious health problem that affects 33 million persons globally. With the increase in life expectancy, the prevalence of dementia is expected to reach 81.1 million persons by 2040. Dementia impairs quality of life and is associated with profound disease burden, morbidity, and mortality in both patients and caregivers. Therefore, identifying measures to prevent dementia is a research priority. Midlife hypertension has increased the risk of dementia in large prospective cohort studies. Researchers have investigated the blood pressure-lowering effects of antihypertensive drugs on the incidence of dementia. Although prospective cohort studies have shown that use of antihypertensive drugs was associated with a reduced rate of cognitive impairment and dementia, these studies were not placebo controlled. Four randomized, placebo-controlled studies-the Systolic Hypertension in Europe (Syst-Eur) study, Study on Cognition and Prognosis in the Elderly (SCOPE), Systolic Hypertension in the Elderly Program (SHEP), and Perindopril Protection Against Recurrent Stroke Study (PROGRESS)-investigated the effects of antihypertensive agents on the incidence of dementia. The Syst-Eur study found that active treatment with nitrendipine, enalapril, and/or hydrochlorothiazide reduced the rate of dementia by 50% compared with placebo (p=0.05). The PROGRESS study showed that active treatment with perindopril and indapamide was associated with reduced cognitive decline compared with placebo (risk ratio 19%, p=0.01). In contrast, the SCOPE study (candesartan or hydrochlorothiazide vs placebo) and the SHEP trial (chlorthalidone, atenolol, or reserpine vs placebo) found no significant difference between the active treatment and placebo groups on the incidence of dementia. Some researchers have suggested that certain antihypertensive drug classes, such as angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, diuretics, and calcium channel blockers, may offer benefit in reducing dementia risk in addition to their blood pressure-lowering effect. Further prospective randomized studies comparing different antihypertensive classes are needed to provide more evidence regarding the effects of antihypertensive drugs on dementia risk and to determine whether certain antihypertensive classes provide greater benefits than others.