Zestril is a brand name for lisinopril, a blood pressure medication approved to treat three conditions: high blood pressure, heart failure, and survival after a heart attack. It belongs to a class of drugs called ACE inhibitors, which are considered first-line treatment for hypertension by the American Heart Association and American College of Cardiology.
How Zestril Works
Your body has a built-in system for regulating blood pressure called the renin-angiotensin-aldosterone system. Part of this system involves an enzyme that converts a relatively harmless substance (angiotensin I) into a powerful one (angiotensin II) that tightens blood vessels and tells your kidneys to retain sodium and water. Zestril blocks that enzyme, so less of the vessel-tightening substance gets produced. Blood vessels relax, fluid retention drops, and blood pressure comes down.
This same mechanism is why the drug helps in heart failure. When your heart is struggling to pump effectively, reducing the workload by relaxing blood vessels and lowering fluid volume makes each heartbeat more efficient.
High Blood Pressure
Zestril is approved for treating high blood pressure in adults and children aged 6 and older. For most adults, the starting dose is 10 mg taken once a day, with a typical maintenance range of 20 to 40 mg daily. If you’re already taking a diuretic (water pill), the starting dose is usually lower at 5 mg to prevent your blood pressure from dropping too far, too fast.
One practical advantage of Zestril is its once-daily dosing. You don’t need to remember multiple pills throughout the day. Doses up to 80 mg have been studied, but they don’t appear to lower blood pressure more than 40 mg does, so most people stay at or below that threshold.
Heart Failure
Zestril is used alongside other medications, typically diuretics, to reduce symptoms of heart failure where the heart muscle has weakened and can’t pump as strongly as it should. The starting dose for heart failure is lower than for blood pressure, usually 5 mg once daily, gradually increased to a maximum of 40 mg as tolerated. For people with low sodium levels, the starting dose drops further to 2.5 mg.
The “as tolerated” part matters here. In heart failure, the body is often more sensitive to blood pressure changes, so doctors typically increase the dose slowly over weeks while monitoring how you respond.
After a Heart Attack
Zestril is also approved to reduce the risk of death when given to stable patients within 24 hours of a heart attack. The goal is to limit the damage to heart muscle and prevent the heart from remodeling (changing shape in ways that weaken it further) in the weeks and months following the event. This use is typically started in a hospital setting and continued as part of long-term recovery.
Common Side Effects
The most well-known side effect of Zestril, and ACE inhibitors in general, is a persistent dry cough. Studies report that anywhere from 4% to 35% of people taking these drugs develop it. The cough is dry, tickly, and unproductive. It can start weeks or even months after beginning the medication and goes away after stopping it. For many people the cough is mild enough to tolerate, but for others it’s the reason they switch to a different class of blood pressure drug.
A rarer but more serious side effect is angioedema, a sudden swelling of the face, lips, tongue, or throat that can interfere with breathing. This is a medical emergency. If you’ve ever had angioedema from any ACE inhibitor, Zestril is off-limits. People with a hereditary tendency toward this type of swelling also cannot take it.
Pregnancy Warning
Zestril carries the FDA’s most serious warning label regarding pregnancy. When taken during the second and third trimesters, ACE inhibitors can cause severe injury or death to the developing baby, including kidney failure, low amniotic fluid, skull abnormalities, and underdeveloped lungs. There is also some evidence suggesting risk during the first trimester. If you become pregnant while taking Zestril, it should be stopped as soon as possible.
Important Drug Interactions
Because Zestril affects how your kidneys handle sodium and potassium, combining it with other drugs that raise potassium levels can push you into a dangerous range. Potassium-sparing diuretics and potassium supplements both carry this risk, which is why potassium levels need periodic blood testing while you’re on the medication.
NSAIDs like ibuprofen and naproxen can reduce Zestril’s effectiveness and strain the kidneys when used together. If you take lithium for a mood disorder, Zestril can decrease your body’s ability to clear it, potentially pushing lithium to toxic levels. Your kidney function and electrolytes should be checked regularly, especially early in treatment or whenever another medication is added.
Who Should Not Take Zestril
Beyond the pregnancy restriction and angioedema history, Zestril cannot be combined with a drug called aliskiren in people who have diabetes. This combination raises the risk of dangerously low blood pressure, high potassium, and kidney problems. People with significantly impaired kidney function may still use Zestril in some cases, but they require closer monitoring and often lower doses.