Efficacy of Losartan + Amlodipine Compared to Amlodipine Alone in the Treatment of Uncontrolled High Blood Pressure (MK-0954F-399)

Inclusion criteria * Participants with essential hypertension: * who are on single drug therapy * who are newly diagnosed and not yet taking any drug therapy, or have not had any drug therapy for at least 2 weeks prior to entering study * who have blood pressure readings of 90mmHg ≤ MSDBP \< 110mmHg and 140mmHg ≤ MSSBP \<180mmHg after 2 weeks wash-out for patients on single agent. * Randomization (Visit 3) * After dosing of amlodipine 5mg for 6 weeks, blood pressure readings are: * 90mmHg ≤ MSDBP \< 110mmHg and 140mmHg ≤ MSSBP \< 180mmHg. Exclusion criteria * Participant with MSDBP ≥ 110mmHg or MSSBP ≥ 180mmHg. * Participant currently taking ≥ 2 antihypertensive medications (note: fixed-dose combination medicine should be counted as the number of active ingredients). * Participant with known secondary hypertension of any etiology. * Participant with malignant hypertension or current evidence of impending or active malignant hypertension, including headache, papilledema, cardiac ischemia, or pulmonary congestion precipitated by elevated blood pressure. * Participant with known intolerance, contraindication or hypersensitivity to any component of dihydropyridines, angiotensin II receptor blockers. * Participant showing positive in pregnancy test, lactating woman, or woman who intends to get pregnant during the study period.