The purpose of this study is to determine whether chlorthalidone is more effective than
hydrochlorothiazide at preventing cardiovascular outcomes in Veterans over age 65 with
hypertension. Both medications are thiazide-type diuretics that have been used for more than
50 years and are considered first-line treatment for hypertension. Patients currently
prescribed hydrochlorothiazide will be randomized to either continue taking
hydrochlorothiazide or to receive chlorthalidone, and followed for major cardiovascular
events, such as myocardial infarction (MI) and stroke. The study will use a new, efficient
and less expensive study design termed 'point of care', in which study operations will be
conducted centrally and patient data will be collected passively through the electronic
medical record.