OBJECTIVE To assess the effects of weight reduction with 10mg of sibutramine or placebo on blood pressure during 24 hours (ambulatory blood pressure monitoring), on left ventricular mass, and on antihypertensive therapy in 86 obese and hypertensive patients for 6 months. METHODS The patients underwent echocardiography, ambulatory blood pressure monitoring, and measurement of the levels of hepatic enzymes prior to and after treatment with sibutramine or placebo. RESULTS The group using sibutramine had a greater weight loss than that using placebo (6.7% versus 2.5%; p<0.001), an increase in heart rate (78.3 +/- 7.3 to 82 +/- 7.9 bpm; p=0.02), and a reduction in the left ventricular mass/height index (105 +/- 29.3 versus 96.6 +/- 28.58 g/m; p=0.002). Both groups showed similar increases in the levels of alkaline phosphatase and comparable adjustments in antihypertensive therapy; blood pressure, however, did not change. CONCLUSION The use of sibutramine caused weight loss and a reduction in left ventricular mass in obese and hypertensive patients with no interference with blood pressure or with antihypertensive therapy.