T he objectives of antihypertensive treatment are to prevent the occurrence of cardiovascular diseases, and consequent functional impairment and death. 1,2 According to the results from several clinical trials, the relative risk of stroke decreases by 30-40% and that of ischemic heart diseases by 15-20%, with a reduction of 10-20 mm Hg in the systolic blood pressure (BP) and 5-10 mm Hg diastolic BP. 1,2 Several classes of antihypertensive drugs are available today; among them, the drugs to be used as a first line of treatment should be selected from Ca channel blockers, angiotensin receptor blockers (ARBs), angiotensin-converting enzyme inhibitors, diuretics, and b-blockers. Although all these drugs provide a sufficient hypotensive effect and can prevent the occurrence of cardiovascular diseases, the real-world results have been the unsatisfactory, that is, only 20-30% of the overall hypertensive population can achieve a satisfactory BP reduction (to the target values of o140/90 mm Hg) by the use of any one agent alone, with the exception of subjects with grade 1 hypertension. 3,4 Furthermore, our previous studies conducted in treated hypertensive patients (the Jichi Morning Hypertension Research (J-MORE) study, n¼969) showed that only about 20% of our outpatients were adequately controlled based on both office BP and out-of-office BP (home systolic BPo135 mm Hg) measurement. 5 Recent large clinical trials have demonstrated that the majority of patients require two or more antihypertensive drugs from different classes to achieve the target BP levels. 6-8 As a result, several combination therapies using two drugs in fixed doses have been introduced, and a three-drug preparation that combines a Ca channel blocker, an ARB, and a thiazide diuretic has also recently been made available. There is evidence to suggest that a combination of antihypertensive drugs can have potential benefits attributable to possible synergistic pharmacological and physiological actions. 9,10 In fact, a recent meta-analysis of combination therapy has suggested that low doses of two or three drugs may be preferable to standard doses of one or two drugs, that is, the average reduction in systolic/diastolic BP was 9/6 mm Hg by one drug at the standard dose, and 11/ 7 mm Hg by one drug at twice the standard dose, whereas the average reduction in BP by two drugs even at a half dose was 13/ 7 mm Hg. 10 Furthermore, the adverse effects associated with the use of combinations of two drugs were reported to be less severe than the additive adverse effects from the administration of the two drugs independently. In that analysis, a clear dose-dependent adverse reaction could be seen for thiazide, Ca channel blockers, and b-blockers, but not for ARBs. In particular, therapy with twice the standard dose of thiazide, Ca channel blockers, or b-blockers had pronounced adverse effects (9-18%), whereas adverse effects were observed in only 2% of patients receiving twice the standard dose of ARBs. This means that the BP-lowering effects of ARBs were dose-depe...