Olmark-H Tablet is a combination antihypertensive medication containing Hydrochlorothiazide 12.5 mg and Olmesartan Medoxomil 20 mg. Hydrochlorothiazide is a thiazide diuretic that promotes the excretion of sodium and water by inhibiting sodium reabsorption in the distal convoluted tubules of the kidneys, thereby reducing blood volume and lowering blood pressure. Olmesartan Medoxomil is an angiotensin II receptor blocker (ARB) that selectively inhibits the binding of angiotensin II to the AT1 receptor, preventing vasoconstriction and aldosterone secretion, leading to vasodilation and decreased peripheral resistance. The combination of these two agents provides a complementary mechanism of action, enhancing antihypertensive efficacy. Olmark-H is indicated for the treatment of essential hypertension, particularly in patients who require more than one agent to achieve adequate blood pressure control. It may also reduce the risk of cardiovascular events associated with hypertension. The medication should be used under medical supervision, with monitoring of blood pressure, renal function, and electrolyte levels, especially potassium, due to the risk of hypokalemia or hyperkalemia. Caution is advised in patients with renal or hepatic impairment, and it is contraindicated during pregnancy. Adverse effects may include dizziness, headache, fatigue, and gastrointestinal disturbances.