Olmesartan belongs to the angiotensin II receptor blocker (ARB) family of drugs, which also includes telmisartan, candesartan, losartan, valsartan, and irbesartan. ARBs selectively bind to angiotensin receptor 1 (AT1) and prevent the protein angiotensin II from binding and exerting its hypertensive effects, which include vasoconstriction, stimulation and synthesis of aldosterone and ADH, cardiac stimulation, and renal reabsorption of sodium, among others. Overall, olmesartan's physiologic effects lead to reduced blood pressure, lower aldosterone levels, reduced cardiac activity, and increased excretion of sodium. Olmesartan also affects the renin-angiotensin aldosterone system (RAAS), which plays an important role in hemostasis and regulation of kidney, vascular, and cardiac functions. Pharmacological blockade of RAAS via AT1 receptor blockade inhibits negative regulatory feedback within RAAS, which is a contributing factor to the pathogenesis and progression of cardiovascular disease, heart failure, and renal disease. In particular, heart failure is associated with chronic activation of RAAS, leading to inappropriate fluid retention, vasoconstriction, and ultimately a further decline in left ventricular function. ARBs have been shown to have a protective effect on the heart by improving cardiac function, reducing afterload, increasing cardiac output and preventing ventricular hypertrophy and remodelling. By comparison, the angiotensin-converting enzyme inhibitor (ACEi) class of medications (which includes drugs such as ramipril, lisinopril, and perindopril) inhibit the conversion of angiotensin I to angiotensin II through inhibition of the ACE enzyme. However, this does not prevent the formation of all angiotensin II within the body. The angiotensin II receptor blocker (ARB) family of drugs unique in that it blocks all angiotensin II activity, regardless of where or how it was synthesized. Olmesartan is commonly used for the management of hypertension and Type 2 Diabetes-associated nephropathy, particularly in patients who are unable to tolerate ACE inhibitors. ARBs such as olmesartan have been shown in a number of large-scale clinical outcomes trials to improve cardiovascular outcomes including reducing risk of myocardial infarction, stroke, the progression of heart failure, and hospitalization. Like other ARBs, olmesartan blockade of RAAS slows the progression of diabetic nephropathy due to its renoprotective effects. Orally available olmesartan is produced as the prodrug olmesartan medoxomil which is rapidly converted in vivo to the pharmacologically active olmesartan. It was developed by Daiichi Sankyo Pharmaceuticals and approved in 2002.