Lisinopril (Zestril) is an angiotensin-converting enzyme inhibitor, or ACE inhibitor. It's used to treat high blood pressure in people 6 years and older. In adults, it's also approved to manage heart failure and to lower the risk of death after a heart attack. Lisinopril (Zestril) comes as a tablet that's taken by mouth once daily. There's also an oral solution available under the brand name Qbrelis. Some side effects include dizziness, cough, and headache.