An ACE inhibitor is a type of blood pressure medication that works by blocking an enzyme your body uses to tighten blood vessels. ACE stands for angiotensin-converting enzyme. These are among the most commonly prescribed drugs for cardiovascular and kidney disease, and they’ve been a cornerstone of heart treatment for decades.
How ACE Inhibitors Work
Your body has a built-in system for regulating blood pressure called the renin-angiotensin system. Here’s the short version: your kidneys release an enzyme called renin, which triggers a chain reaction that ultimately produces a substance called angiotensin II. Angiotensin II is a powerful blood vessel constrictor. It squeezes your arteries tighter, which raises blood pressure.
ACE inhibitors interrupt this chain. They block the enzyme that converts the inactive precursor (angiotensin I) into the active form (angiotensin II). With less angiotensin II circulating, your blood vessels relax and widen, and your blood pressure drops. At the same time, your kidneys excrete more salt and water because the drug also reduces levels of aldosterone, a hormone that tells your kidneys to hold onto sodium.
There’s a second effect that matters clinically. The same enzyme that produces angiotensin II also breaks down a substance called bradykinin, which naturally relaxes blood vessels. When you block the enzyme, bradykinin sticks around longer and contributes to the blood pressure lowering effect. This bradykinin accumulation is also responsible for the most well-known side effect of ACE inhibitors: a persistent dry cough.
What ACE Inhibitors Treat
High blood pressure is the most common reason these drugs are prescribed, but the list of uses is broad. ACE inhibitors lower both systolic and diastolic blood pressure, and they do so in people with hypertension as well as those with normal blood pressure who need cardiac protection for other reasons.
In heart failure, ACE inhibitors reduce mortality and hospitalizations by 25% to 40%, according to data published by the American Heart Association. Guidelines recommend starting them without delay after a heart attack in patients with reduced heart function. For people with diabetes, ACE inhibitors (or a closely related class called ARBs) are recommended as first-line blood pressure treatment because of their added kidney-protective benefits.
Kidney disease is the other major use. ACE inhibitors reduce pressure inside the tiny filtering units of the kidneys by selectively widening certain blood vessels there. This slows the progression of kidney damage, particularly in people with diabetes. In studies following patients for more than five years, those taking an ACE inhibitor either stabilized or reduced the amount of protein leaking into their urine, while those on placebo saw steady increases. One study found that the ACE inhibitor lisinopril reduced urinary protein loss by 55% compared to 15% with another type of blood pressure drug. This protective effect appears to work partly through a mechanism independent of blood pressure lowering alone.
Common ACE Inhibitor Medications
The FDA lists ten ACE inhibitors currently approved in the United States. You’ll likely recognize them by their generic names, which all end in “-pril”:
- Lisinopril (Zestril, Prinivil)
- Enalapril (Vasotec)
- Ramipril (Altace)
- Benazepril (Lotensin)
- Captopril (Capoten)
- Fosinopril (Monopril)
- Quinapril (Accupril)
- Perindopril (Aceon)
- Moexipril (Univasc)
- Trandolapril (Mavik)
Lisinopril and enalapril are the most widely prescribed. All work through the same basic mechanism, though they differ in how long they last, how quickly they kick in, and whether they’re taken once or twice daily.
Side Effects
The signature side effect is a dry, persistent cough. It’s caused by the buildup of bradykinin in the lungs, and reported rates range from about 4% to 35% of patients depending on the study. The cough is typically tickly and nonproductive, meaning nothing comes up. It can start weeks or even months after beginning the medication. If it becomes bothersome enough, switching to an ARB (which lowers blood pressure through a similar pathway without affecting bradykinin) usually resolves it.
A more serious but uncommon reaction is angioedema, a rapid swelling of the lips, tongue, throat, or face. This occurs in roughly 0.7% of patients over five years of use. Most cases happen within the first year, with about 0.23% of patients affected during that period. Black and Hispanic patients face a significantly higher risk. In one large study of nearly 135,000 patients, Black race was present in 19.6% of angioedema cases compared to 5.9% of the overall population taking the drug. People with a history of allergy to NSAIDs (common pain relievers like ibuprofen) also had a higher incidence. Angioedema involving the throat is a medical emergency because it can obstruct breathing.
High potassium is the other concern to watch for. Because ACE inhibitors reduce aldosterone (which normally helps your kidneys excrete potassium), potassium levels can creep up. This is particularly relevant if you have kidney disease. The National Kidney Foundation defines a potassium level above 5.0 as elevated in this context and recommends preventive attention once levels reach 4.5. Your doctor will typically check your potassium and kidney function within 4 to 12 weeks of starting the drug, then every 6 to 12 months once your dose is stable. People with reduced kidney function or potassium levels that are already on the higher side get checked more frequently.
Pregnancy Risks
ACE inhibitors are contraindicated during pregnancy. In the second and third trimesters, these drugs inhibit the developing baby’s kidney function, which reduces the fluid surrounding the fetus. This can lead to underdeveloped lungs, limb contractures, and other birth defects from compression. Data from the European Society of Cardiology’s pregnancy registry found that even first-trimester use was associated with a 3.2 times higher risk of congenital anomalies. Women who are planning to become pregnant or who discover a pregnancy while taking an ACE inhibitor should discuss alternative medications promptly.
Taking ACE Inhibitors
Food and antacids can reduce how well your body absorbs ACE inhibitors by slowing stomach emptying and changing stomach acid levels. Some ACE inhibitors are best taken on an empty stomach for this reason, though the specifics vary by drug. Your pharmacist can tell you whether yours should be taken with or without food.
Most people start on a low dose that gets gradually increased. The goal is to reach a target dose that provides the full protective benefit while keeping side effects manageable. If you’re prescribed an ACE inhibitor for heart failure or kidney protection, staying on it long-term is typically part of the plan, since the benefits in slowing disease progression depend on continued use. Stopping abruptly can cause a rebound increase in blood pressure, so any changes should be gradual and guided by your prescriber.