In this study, adult patients will submit serum and 24 hour urine samples prior to HCTZ cessation and at the following intervals after cessation: 4-6 days, 14-16 days, 28-30 days, adn 90-92 days. To minimize confounding variable, patients will take supplemental Vitamin D and Calcium, monitor their daily calcium intake, and monitor blood pressure weekly. Alternative, non-diuretic, antihypertensive medication(s) may be prescribed at the discretion of the enrolling provider.