Effects of Combination Therapy With Alpha-1 Blocker (Bunazosin or Doxazosin) in the Treatment of Patients With Mild to Moderate Essential Hypertension

Inclusion Criteria: Subjects with mild to moderate essential hypertension, with the following criteria: 1. Washout period (Week -2) * Male or female subjects aged 20 to 80 years * Systolic blood pressure (SBP):140 mm Hg but \<180 mm Hg and/or diastolic blood pressure (DBP):90 mm Hg but \<110 mm Hg * Subjects who have given written informed consent prior to participation in the trial and who undertake to comply with the protocol 2. Angiotensin II antagonist mono-therapy period (week 0) * Subjects with systolic blood pressure \>= 140 mm Hg but \<180 mm Hg and/or diastolic blood pressure \>= 90 mm Hg but \<110 mm Hg * Presence of any 2 of the following 4 risk factors * Waist circumference: male \> 90 cm, female \> 80 cm * Triglycerides \>= 150 mg/dl * HDL cholesterol: male \< 40 mg/dl, female \< 50 mg/dl * Fasting glucose \>= 110 mg/dl 3. Angiotensin II antagonist with add-on Bunazosin or Doxazosin treatment period (Week 5) * SBP \>=140 mm Hg or decrease \< 10 % OR * DBP \>=90 mm Hg or decrease \< 10 % comparing the blood pressure at the entry of the Angiotensin II antagonist mono-therapy period. Exclusion Criteria: Subjects with the following conditions are not eligible for participation： a) Washout period (Week -1 or -2) * Subjects with severe hypertension (SBP\>=180 mm Hg or DBP\>=110 mm Hg). * Subjects who have proven or suspected hypersensitivity to quinazoline derivatives * Subjects who have a history of alcohol or drug abuse. * Subjects with past or present evidence of cancer * Subjects who have a past history of arterial fibrillation, heart failure (LVEF\<40%), acute coronary syndrome, myocardial infarction, stroke or severe arrhythmia. * Subjects who are severely obese (BMI\>30 kg/m2) * Women who are pregnant or lactating or suspected of being pregnant. * Subjects who have previously participated in any clinical trial of new or unapproved substances within the 12 weeks before starting of washout period * Subjects on other anti-hypertensive or lipid-lowering medication * Inability to return for scheduled visits or comply with any other aspect of the Protocol * Subjects with poorly controlled diabetes mellitus (HbA1c \> 10%) * Subjects with concurrent serious hepatic or renal disorders (defined as AST and/or ALT \> 3 times upper normal limit or Cr \> 2mg/dl). * Subjects who, in the opinion of the investigators, are poor medical candidates or pose any other risk for therapy with an investigational drug.