List of products in the National Drug Code with proprietary name . This medication is used to treat high blood pressure. Lowering high blood pressure helps prevent strokes, heart attacks, and kidney problems. Chlorothiazide is a "water pill" (diuretic) that causes you to make more urine. This helps your body get rid of extra salt and water. This medication is also used to decrease swelling (edema) caused by conditions such as cancer, congestive heart failure, liver disease, and kidney disease. This effect can help your kidneys work better and lessen symptoms such as trouble breathing and swelling in your ankles, feet, hands, or belly.