Inclusion Criteria:

• Male or female aged 18 years or older.
• Mean trough seated systolic blood pressure (SeSBP) of ≥ 160/100 mmHg (SeSBP of ≥ 160 mmHg and seated diastolic blood pressure (SeDBP) ≥ 100 mmHg) at screening if not currently on antihypertensive medication (e.g. newly diagnosed subjects)

OR:

For subjects on monotherapy: mean trough SeSBP of ≥ 150/95 mmHg (SeSBP of ≥ 150 mmHg and SeDBP ≥ 95 mmHg) at screening

OR:

For subjects on any combination of antihypertensive medications that includes either hydrochlorothiazide or amlodipine or olmesartan for a duration of at least four weeks: mean trough SeSBP of ≥ 140/90 mmHg (SeSBP of ≥ 140 mmHg and SeDBP ≥ 90 mmHg) at screening

OR:

For subjects on any other combination of antihypertensive medications that includes neither hydrochlorothiazide, amlodipine nor olmesartan: mean trough SeSBP ≥ 160 mmHg, mean trough SeDBP ≥ 100mmHg, at the end of the taper-off period

• Subject freely signs the Informed Consent Form (ICF) after the nature of the study and the disclosure of his/her data has been explained.
• Female subjects of childbearing potential must be using adequate contraception (female of childbearing potential is defined as one who has not been postmenopausal for at least one year, or has not been surgically sterilised, or has not had a hysterectomy at least three months prior to the start of this study [Visit 1]). Females taking oral contraceptives should have been on therapy for at least three months. Adequate contraceptives include hormonal intra-uterine devices, hormonal contraceptives (oral, depot, patch or injectable), and double barrier methods such as condoms or diaphragms with spermicidal gel or foam. If a female becomes pregnant during the study, she has to be withdrawn immediately.

Exclusion Criteria:

• Female subjects of childbearing potential who are pregnant or lactating.
• Subjects with serious disorders which may limit the ability to evaluate the efficacy or safety of the investigational products, including cerebrovascular, cardiovascular, renal, respiratory, hepatic, gastrointestinal, endocrine or metabolic, haematological or oncological, neurological, and psychiatric diseases. The same applies for immunocompromised and/or neutropenic subjects.
• Subjects having a history of the following within the last six months: myocardial infarction (MI), unstable angina pectoris, percutaneous coronary intervention, heart failure, hypertensive encephalopathy, cerebrovascular accident (stroke), or transient ischaemic attack.

• Subjects with clinically significant abnormal laboratory values at Screening, including subjects with one or more of the following:

  • Aspartate aminotransferase (AST) > 3 times upper limit of normal (ULN)
  • Alanine aminotransferase (ALT) > 3 times ULN
  • Gamma-glutamyltransferase (GGT) > 3 times ULN
  • Potassium above ULN (unless high value is due to haemolytic blood sample)
• Subjects with secondary hypertension of any aetiology such as renal disease, phaeochromocytoma, or Cushing's syndrome.
• Subjects with contraindication to olmesartan, amlodipine, hydrochlorothiazide, or any of the excipients.
• Subjects with a mean SeSBP > 200 mmHg or mean SeDBP > 115 mmHg or bradycardia (heart rate < 50 beats/min at rest documented by mean radial pulse rate [PR] or electrocardiogram [ECG]) at Screening (Visit 1) or immediately before taking Period I study medication (Visit 2).