Losartan—sold under the brand name Cozaar among others—belongs to a class of medications called angiotensin II receptor blockers (ARBs). ARBs work by blocking the action of a chemical called angiotensin which narrows the arteries. Losartan is commonly used to treat high blood pressure and is sometimes combined with other medicines, like hydrochlorothiazide. Here’s more on what you need to know about losartan, its primary uses, and what side effects to be aware of before taking the drug.