Losartan HCTZ 50 12.5mg is a combination medication used to treat high blood pressure (hypertension) . It contains two active ingredients, losartan and hydrochlorothiazide. Losartan is an angiotensin II receptor blocker that helps to relax and widen blood vessels, which lowers blood pressure. Hydrochlorothiazide is a diuretic that helps to remove excess salt and water from the body, which also helps to lower blood pressure. This medication is usually not the first medicine used to treat hypertension, except when hypertension is severe enough that the benefit of achieving prompt blood pressure control exceeds the risk of initiating combination therapy. It may also be used to reduce the risk of stroke in certain people with heart disease.