CS-8635 combines three widely prescribed antihypertensive medications, olmesartan medoxomil(OM), amlodipine (AML), and hydrochlorothiazide (HCTZ), to lower blood pressure. The purpose of the study is to evaluate the efficacy and safety of triple therapy with CS-8635 compared with dual therapy in Korean patients with hypertension not controlled with dual fixed dose combination therapy (Olmetec® Plus). The treatments that will be used in this study are as follows: Run-in period -OM/HCTZ 20/12.5 mg (Olmetec® Plus 20/12.5 mg) ; Double blind treatment period - OM/AML/HCTZ 20/5/12.5mg (CS8635 20/5/12.5mg) + its matching placebo vs.OM/HCTZ 20/12.5mg (Olmetec® Plus 20/12.5 mg) + its matching placebo; Open label extension period - OM/AML/HCTZ 40/5/12.5mg (CS8635 40/5/12.5mg) or OM/AML/HCTZ 20/5/12.5mg (CS8635 20/5/12.5mg).

Please refer to arms, outcome measures and eligibility criteria for details.

Inclusion Criteria for Screening

• Male or female at the age of 20 to 75 years
• Voluntary written informed consent to participation in this study
• Patients with hypertension either newly diagnosed or without treatment of antihypertensive drugs within 4 weeks of screening, who have mean seated diastolic blood pressure (msDBP) ≥ 100 mmHg at screening, or
• Patients who have been on a stable dose of antihypertensive drugs for at least 4 weeks before run-in period and meet the following blood pressure criteria at screening: Monotherapy: msDBP ≥ 95 mmHg, or Dual combination therapy: msDBP ≥ 90 mmHg, or Triple combination therapy: 70 mmHg ≤ msDBP < 90 mmHg

Inclusion criteria for randomization

• msSBP/DBP at randomization: msSBP ≥ 140 mmHg (msSBP ≥ 130 mmHg in subjects with diabetes or chronic renal disease), and msDBP ≥ 90 mmHg (msDBP ≥ 80 mmHg in subjects with diabetes or chronic renal disease)

Exclusion Criteria:

• msDBP ≥ 115mmHg or msSBP ≥ 200 mmHg measured at screening and randomization
• Patients with mini-max blood pressure difference of SeSBP ≥ 20 mmHg or SeDBP ≥ 10 mmHg in the chosen arm at screening
• Patients with blood pressure difference of SeSBP ≥ 20 mmHg and SeDBP ≥ 10 mmHg in both arms at screening
• Patients with hypersensitivity to the investigational product or any of its components
• Patients with medical history or hypersensitivity to sulfonamide, dihydropyridine, or thiazide diuretics
• History of secondary hypertension or history of any of the diseases suspected of secondary hypertension
• Symptomatic orthostatic hypotension
• Uncontrolled diabetes mellitus
• Severe heart disease, or ischemic heart disease, peripheral vascular disease
• Clinically significant ventricular tachycardia, atrial fibrillation, atrial flutter, or other arrhythmia considered clinically significant
• Hypertrophic obstructive cardiomyopathy, severe obstructive coronary artery disease, aortic stenosis, or hemodynamically significant stenosis on aortic valve or mitral valve.
• Severe cerebrovascular disorder
• Known moderate or malignant retinopathy
• Consumption disease , autoimmune disease, or connective tissue disease
• Patients requiring chronic anti-inflammatory treatment
• Anuria or severe renal failure
• Severe hepatic failure, AST or ALT > 3 times the upper limit of normal, biliary obstruction, biliary cirrhosis, or cholestasis
• Patients who have been treated for hyponatremia, hypokalemia, hyperkalemia, hypercalcemia, or symptomatic hyperuricemia
• Addison's disease
• Glucose-galactose malabsorption, galactose intolerance, or Lapp lactase deficiency
• Gastrointestinal tract disease or surgical operation that may affect absorption, distribution, metabolism, and excretion of drugs, presence of active gastritis or gastrointestinal/rectal bleeding considered clinical significant by the investigator, active inflammatory bowel syndrome within the last 12 months, etc
• Patients with history of or suspected of drug or alcohol abuse
• Pregnant or lactating women, or women of childbearing potential who do not agree to use appropriate contraceptive methods such as progestin hormone therapy (Oral, implant), intrauterine device, barrier methods of contraception (condom or occlusive cap (diaphragm or cervical/vault caps) with spermicide), male sterilisation or true abstinence
• Patients who participated in other clinical study within 1 month prior to screening
• Patients considered to be incapable of complying with the protocol

De-identified individual participant data (IPD) and applicable supporting clinical trial documents may be available upon request at https://vivli.org/. In cases where clinical trial data and supporting documents are provided pursuant to our company policies and procedures, Daiichi Sankyo will continue to protect the privacy of our clinical trial participants. Details on data sharing criteria and the procedure for requesting access can be found at this web address: https://vivli.org/ourmember/daiichi-sankyo/

Studies for which the medicine and indication have received European Union (EU) and United States (US), and/or Japan (JP) marketing approval on or after 01 January 2014 or by the US or EU or JP Health Authorities when regulatory submissions in all regions are not planned and after the primary study results have been accepted for publication.

Formal request from qualified scientific and medical researchers on IPD and clinical study documents from clinical trials supporting products submitted and licensed in the United States, the European Union and/or Japan from 01 January 2014 and beyond for the purpose of conducting legitimate research. This must be consistent with the principle of safeguarding study participants' privacy and consistent with provision of informed consent.