Losartan is an angiotensin II receptor antagonist drug used mainly to treat high blood pressure (hypertension). Losartan was the first angiotensin II antagonist to be marketed. As with all angiotensin II type 1 receptor (AT1) antagonists, losartan is indicated for the treatment of hypertension. It may also delay progression of diabetic nephropathy and is associated with a positive clinical outcome in that regard. Although clinical evidence shows calcium channel blockers and thiazide-type diuretics are preferred first-line treatments for most patients, an angiotensin II receptor antagonist such as losartan is recommended as first-line treatment in patients under the age of 55 who cannot tolerate an ACE inhibitor. Losartan is also available as hydrochlorothiazide/losartan, a combination drug with a low dose thiazide diuretic to achieve an additive antihypertensive effect.