List of products in the National Drug Code with proprietary name . Captopril is used to treat high blood pressure (hypertension). Lowering high blood pressure helps prevent strokes, heart attacks, and kidney problems. It is also used to treat heart failure, protect the kidneys from harm due to diabetes, and to improve survival after a heart attack. Captopril is an ACE inhibitor and works by relaxing blood vessels so that blood can flow more easily.