An ACE inhibitor is a type of blood pressure medication that works by blocking an enzyme your body uses to tighten blood vessels. The name stands for angiotensin-converting enzyme inhibitor. These drugs are among the most commonly prescribed medications worldwide, used primarily for high blood pressure and heart failure. On average, they lower systolic blood pressure (the top number) by about 8 points and diastolic (the bottom number) by about 5 points.
How ACE Inhibitors Work
Your body has a built-in system for regulating blood pressure. As part of that system, an enzyme called ACE converts a relatively inactive molecule (angiotensin I) into a powerful one called angiotensin II. Angiotensin II does two things that raise blood pressure: it forces blood vessels to constrict, and it triggers your body to retain sodium and water by increasing a hormone called aldosterone.
ACE inhibitors block that conversion step. With less angiotensin II circulating, your blood vessels relax and widen, fluid retention decreases, and blood pressure drops. The effect is steady rather than dramatic, which is why these medications are taken daily rather than as needed.
Common ACE Inhibitor Medications
The FDA lists ten ACE inhibitors currently available. The most widely prescribed is lisinopril (sold as Zestril and Prinivil), followed by enalapril (Vasotec), ramipril (Altace), and benazepril (Lotensin). Others include captopril (Capoten), fosinopril (Monopril), moexipril (Univasc), perindopril (Aceon), quinapril (Accupril), and trandolapril (Mavik).
All of them work through the same basic mechanism. The differences come down to how long they stay active in your body, how they’re metabolized, and which conditions they’ve been specifically studied for. Your doctor’s choice often depends on cost, dosing convenience, and how you respond.
What ACE Inhibitors Treat
High blood pressure is the most common reason these drugs are prescribed, but they serve several other purposes. Current guidelines from both the American Heart Association and the European Society of Cardiology recommend ACE inhibitors as first-line treatment for people with high blood pressure who also have diabetes, kidney disease, or protein in the urine. The drugs have proven kidney-protective effects in these populations, slowing the progression of damage over time.
ACE inhibitors are also a standard part of treatment after a heart attack and for chronic heart failure. In heart failure, the reduction in blood vessel resistance makes it easier for a weakened heart to pump blood forward. For people with diabetes and early signs of kidney involvement, these medications can help preserve kidney function beyond just lowering blood pressure.
Side Effects to Know About
The most distinctive side effect is a persistent dry cough. It’s not dangerous, but it can be annoying enough to make people stop taking the medication. In clinical trials comparing ACE inhibitors to a similar class of drugs called ARBs, cough accounted for 43% of all reasons people quit their ACE inhibitor, compared to just 4% in the ARB group. The cough happens because the same enzyme that ACE inhibitors block also breaks down a substance called bradykinin. When bradykinin accumulates in the lungs, it irritates the airways.
Other common side effects include dizziness (especially when standing up quickly), elevated potassium levels, and a slight rise in creatinine, a marker of kidney function. Your doctor will typically check your potassium and creatinine levels within a few days to a week of starting the medication, particularly if you have existing kidney problems.
Angioedema: Rare but Serious
The same bradykinin buildup that causes coughing can, in rare cases, trigger angioedema, a rapid swelling of the face, lips, tongue, or throat. This happens in roughly 0.1% to 0.7% of people taking an ACE inhibitor. The swelling occurs because excess bradykinin makes small blood vessels leak fluid into surrounding tissue. If it involves the airway, it can become a medical emergency. Anyone who notices sudden swelling of the face or throat while taking an ACE inhibitor should seek immediate medical attention, and the medication will be permanently discontinued.
Who Should Not Take ACE Inhibitors
Pregnancy is the most important contraindication. ACE inhibitors taken during the second and third trimesters can cause serious harm to the developing baby, including kidney failure, underdeveloped skull bones, dangerously low blood pressure, and underdeveloped lungs. The rate of complications among exposed infants is estimated between 10% and 20%, and some cases progress to death or permanent kidney damage. Women who become pregnant while on an ACE inhibitor are advised to stop the medication before the second trimester.
People who have previously experienced angioedema from any ACE inhibitor should not take one again. The same applies to anyone with a history of a similar type of swelling from other causes. People with certain kidney artery conditions may also need to avoid these drugs because of the risk of a steep drop in kidney function.
ACE Inhibitors vs. ARBs
ARBs (angiotensin receptor blockers) are the closest alternative to ACE inhibitors. Both target the same blood pressure system, but at different points. ACE inhibitors block the creation of angiotensin II, while ARBs block angiotensin II from binding to its receptors. The blood pressure lowering effect is similar.
The practical difference is tolerability. A large Cochrane review found that ARBs are slightly better tolerated, with an absolute risk reduction for quitting due to side effects of 1.8% over about four years. That difference is almost entirely driven by the dry cough. If you develop a persistent cough on an ACE inhibitor, switching to an ARB is the most common next step, and the cough typically resolves. ARBs also carry a much lower risk of angioedema, though it’s not zero.
The two drug classes are never used together. Combining them increases the risk of dangerously low blood pressure and kidney problems without adding meaningful benefit.
What to Expect When Starting One
ACE inhibitors are taken once or twice daily, depending on the specific drug. Most people notice no immediate sensation when they start, unlike some blood pressure medications that cause obvious flushing or fatigue. The blood pressure effect builds over a few days to weeks.
You’ll likely have a blood test within the first week to check kidney function and potassium. A small rise in creatinine (up to about 30% from your baseline) is considered acceptable and expected. Larger increases may prompt your doctor to adjust the dose or consider an alternative. Potassium levels can creep up because the medication reduces aldosterone, the hormone that normally helps your kidneys excrete potassium. This is especially relevant if you’re also taking potassium supplements or potassium-sparing diuretics.
Dizziness in the first few days is common, particularly if you were already on a low-salt diet or taking a diuretic. Rising slowly from sitting or lying positions helps. This effect usually fades as your body adjusts.