Losartan, also known by the brand name Cozaar, is a first-choice medication that's used to lower blood pressure. It's also shown to protect against stroke in certain people. In addition, this medication can slow down the worsening of kidney problems in certain people with diabetes. Losartan (Cozaar) belongs to the drug class called angiotensin II receptor blockers (ARBs). This medication is taken by mouth once daily and is available as a lower-cost generic. Side effects can include dizziness, fatigue, and upper respiratory infections.