An ACE inhibitor is a type of blood pressure medication that works by blocking an enzyme your body uses to tighten blood vessels. By preventing that tightening, these drugs lower blood pressure and reduce strain on the heart. They are one of the most widely prescribed classes of medication in the world, used for high blood pressure, heart failure, and protecting the kidneys in people with diabetes.
How ACE Inhibitors Work
Your body has a built-in system for regulating blood pressure called the renin-angiotensin-aldosterone system, or RAAS. Here’s the short version: your kidneys release an enzyme called renin, which sets off a chain reaction that eventually produces a hormone called angiotensin II. That hormone is a powerful blood vessel constrictor. It also triggers the release of aldosterone, another hormone that makes your kidneys retain salt and water, which raises blood volume and pressure further.
ACE inhibitors interrupt this chain by blocking angiotensin-converting enzyme, the specific enzyme that creates angiotensin II. With less angiotensin II circulating, your blood vessels relax and widen, your body holds on to less salt and water, and your blood pressure drops. There’s a bonus effect too: blocking ACE also slows the breakdown of bradykinin, a substance that helps blood vessels dilate. So ACE inhibitors lower pressure through two pathways at once.
Common ACE Inhibitor Medications
There are about ten ACE inhibitors on the market. They all end in “-pril,” which makes them easy to spot on a prescription label. The most commonly prescribed ones include:
- Lisinopril (brand names Zestril, Qbrelis)
- Enalapril (Vasotec, Epaned)
- Ramipril (Altace)
- Benazepril (Lotensin)
- Captopril (one of the oldest, the first ACE inhibitor approved)
Others include fosinopril, moexipril, perindopril, quinapril, and trandolapril. They all work the same way but differ in how long they stay active in your body, how quickly they take effect, and how they’re processed by the liver and kidneys. Your doctor picks one based on your specific health situation and how often you want to take a pill (some are once daily, others twice).
What ACE Inhibitors Treat
High blood pressure is the most common reason people take ACE inhibitors, but they’re used for several other conditions. In heart failure, the heart is too weak to pump efficiently. ACE inhibitors reduce the workload on the heart by lowering the pressure it has to pump against, which can slow the progression of the disease and improve symptoms like shortness of breath and fatigue.
People who have had a heart attack are often started on an ACE inhibitor to protect the heart muscle from further damage and prevent harmful structural changes in the left ventricle. They’re also prescribed to people with diabetes or chronic kidney disease because lowering the pressure inside the kidneys’ tiny blood vessels helps slow the loss of kidney function over time.
The Dry Cough and Other Side Effects
The most notorious side effect of ACE inhibitors is a persistent, dry, tickly cough. It’s not dangerous, but it can be annoying enough to make people stop taking the medication. The cough happens because the same bradykinin buildup that helps lower blood pressure also irritates the airways. The cough can start weeks or even months after beginning the drug. It goes away once you stop taking it.
Other relatively common side effects include dizziness (especially when standing up quickly, since blood pressure drops), elevated potassium levels, and mild changes in kidney function. The potassium issue matters because potassium levels that climb too high can affect your heart rhythm. This is why doctors typically check blood work, including kidney function and potassium, shortly after starting the medication and periodically afterward. If your potassium rises above a certain threshold, the dose may need to be reduced or the drug stopped.
Angioedema: A Rare but Serious Reaction
A small number of people, roughly 2 in every 1,000 per year, develop angioedema while taking an ACE inhibitor. This is a sudden swelling of the lips, tongue, throat, or face. It can happen at any point during treatment, even after years of taking the medication without problems. In severe cases it can obstruct breathing and requires emergency treatment.
The risk is not equal across all groups. Black patients have a nearly fourfold higher risk of angioedema compared to other populations, and women face about a 50% higher risk than men. If you experience any unusual swelling of your face, lips, or tongue while taking an ACE inhibitor, seek medical attention immediately. People who develop angioedema on an ACE inhibitor should not take one again.
Pregnancy and ACE Inhibitors
ACE inhibitors carry a black box warning, the FDA’s most serious label, regarding use during pregnancy. Taking these drugs during the second and third trimesters can severely harm the developing baby by reducing fetal kidney function. This can lead to dangerously low amniotic fluid, which in turn causes underdeveloped lungs and skeletal deformities. Fetal kidney failure and death are possible outcomes. If you become pregnant while taking an ACE inhibitor, the standard guidance is to stop the medication as soon as pregnancy is confirmed.
How They Compare to ARBs
If you can’t tolerate an ACE inhibitor, usually because of the cough, your doctor will likely switch you to an ARB (angiotensin II receptor blocker). ARBs work on the same blood pressure system but at a different point. Instead of preventing the creation of angiotensin II, they block the receptor that angiotensin II latches onto. The end result is similar: blood vessels relax and pressure drops.
Because ARBs don’t cause bradykinin to build up, they rarely produce a cough. For years, some researchers believed ACE inhibitors had a slight edge because that extra bradykinin also produced beneficial effects on blood vessels, including increased production of nitric oxide, which further relaxes arteries. In practice, large studies have shown the two classes produce very similar outcomes for most patients. The choice often comes down to side effects and individual tolerance.
What to Expect When Starting One
ACE inhibitors are taken as a daily pill, usually once or twice a day. Most people notice the blood pressure effect within a few hours of the first dose, though it takes a couple of weeks of regular use to see the full benefit. Your doctor will likely start you at a lower dose and increase it gradually.
Expect a blood test within a week or two of starting to check your kidney function and potassium levels. If those come back normal, monitoring becomes less frequent, typically every few months to once a year. You should avoid potassium supplements and potassium-rich salt substitutes unless your doctor specifically says otherwise, since ACE inhibitors already raise potassium levels on their own. Nonsteroidal anti-inflammatory drugs like ibuprofen can blunt the blood pressure effect and further stress the kidneys, so mention any over-the-counter pain medications you take regularly.
Most people tolerate ACE inhibitors well for years or even decades. They remain a first-line treatment for high blood pressure and heart failure because they have one of the longest and strongest track records of reducing heart attacks, strokes, and kidney damage in large clinical trials.