Captopril drug molecule, molecular model. Atoms are represented as spheres and colour coded; carbon (light blue), hydrogen (white), oxygen (red), sulphur (yellow) and nitrogen (dark blue). Captopril belongs to a group of drugs, known as ACE inhibitors, that are used to treat hypertension (high blood pressure) and heart failure. They work by inhibiting the production of angiotensin-converting enzyme, which raises blood pressure by causing blood vessels to constrict and promoting the retention of fluid. Due to a short half-life, captopril needs to be administered 2 to 3 times a day and so its use has been largely replaced by longer-acting drugs.