An ARB, short for angiotensin II receptor blocker, is a type of blood pressure medication that relaxes your blood vessels by blocking a hormone that causes them to tighten. ARBs are among the most commonly prescribed drugs for high blood pressure, and they’re also used to treat heart failure and protect the kidneys in people with diabetes. If your doctor recently mentioned an ARB or you spotted the term on a prescription label, here’s what you need to know.
How ARBs Lower Blood Pressure
Your body has a built-in system for regulating blood pressure called the renin-angiotensin-aldosterone system, or RAAS. When your blood pressure drops or your body senses low blood flow, the kidneys release an enzyme that eventually produces a hormone called angiotensin II. This hormone is a powerful blood vessel constrictor: it squeezes your arteries tighter, which raises blood pressure.
ARBs work by blocking the receptor that angiotensin II latches onto (called the AT1 receptor) on the surface of blood vessel walls. With that receptor blocked, angiotensin II can’t do its job. Your blood vessels stay relaxed and open, blood flows more easily, and your blood pressure comes down. This same mechanism also reduces the workload on the heart, which is why ARBs are useful for heart failure too.
What ARBs Are Prescribed For
The primary use is high blood pressure, but ARBs pull double or triple duty for many patients. They’re prescribed for heart failure, to protect kidney function in people with type 2 diabetes, and to reduce protein leaking into the urine (a sign of kidney damage). Some ARBs are also approved for reducing stroke risk in people with an enlarged heart.
The kidney-protective effect is particularly important. In people with kidney disease, angiotensin II raises pressure inside the tiny filtering units of the kidney. ARBs relieve that pressure by relaxing the blood vessels on the exit side of those filters. This reduces protein spillage into the urine and slows further kidney damage, an effect that happens independently of the blood pressure drop itself.
Common ARB Medications
There are seven ARBs available, and you’ll recognize them by their generic names, which all end in “-sartan”:
- Losartan (Cozaar)
- Valsartan (Diovan)
- Irbesartan (Avapro)
- Candesartan (Atacand)
- Olmesartan (Benicar)
- Telmisartan (Micardis)
- Azilsartan (Edarbi)
Losartan and valsartan are the most widely prescribed. All of them work through the same basic mechanism, but they differ in how long they last in the body and how potent they are, so your doctor may try more than one to find the best fit.
How ARBs Differ From ACE Inhibitors
ACE inhibitors (drugs ending in “-pril,” like lisinopril or ramipril) target the same blood pressure system but at an earlier step. They prevent angiotensin II from being produced in the first place. ARBs let the hormone get made but block it from working. The end result on blood pressure is similar, but the side effect profile is noticeably different.
The biggest practical difference is cough. ACE inhibitors cause a persistent dry cough in roughly 4% to 35% of people who take them, depending on the population studied. ACE inhibitors carry about 3.2 times the risk of cough compared to ARBs. In a large trial of over 25,000 participants, 4.2% of people on the ACE inhibitor ramipril discontinued treatment because of cough, compared to just 1.1% on the ARB telmisartan. That’s why ARBs are often the go-to alternative when someone can’t tolerate an ACE inhibitor’s cough. The reason for this gap is that ACE inhibitors cause a buildup of a substance called bradykinin, which irritates the airways. ARBs don’t trigger that buildup.
One important rule: ARBs and ACE inhibitors should not be taken together. Combining them raises the risk of dangerously low blood pressure, kidney problems, and high potassium levels without adding meaningful benefit.
Side Effects
ARBs are generally well tolerated, with a low overall incidence of side effects. The most common issues are dizziness, a drop in blood pressure (especially when standing up), and a rise in potassium levels. Because angiotensin II normally helps the kidneys excrete potassium, blocking it can cause potassium to build up. This risk increases if you’re also taking potassium supplements or potassium-sparing diuretics.
Kidney function needs monitoring, particularly in people who already have kidney disease, severe heart failure, or narrowed arteries supplying the kidneys. In these groups, the kidneys rely heavily on angiotensin II to maintain their filtering pressure, so blocking it can sometimes tip kidney function in the wrong direction. Your doctor will typically check blood work within a few weeks of starting an ARB to make sure your kidneys and potassium levels are stable.
Rare side effects include allergic reactions, liver enzyme changes, and (with olmesartan specifically) a gastrointestinal condition that mimics celiac disease. Unlike ACE inhibitors, ARBs very rarely cause the swelling reaction known as angioedema, though isolated cases have been reported.
Who Should Not Take ARBs
ARBs are contraindicated in pregnancy. Use during pregnancy is associated with serious harm to the developing baby, including skull defects, decreased amniotic fluid, kidney failure, and fetal death. If you’re planning a pregnancy or discover you’re pregnant while on an ARB, the medication needs to be stopped and replaced with a pregnancy-safe alternative.
People with severely reduced kidney function (a filtration rate below about 15 mL/min) may need to avoid ARBs or use them at reduced doses under close supervision, since the risk of high potassium and further kidney decline increases substantially. ARBs also aren’t appropriate for anyone who has had a serious allergic reaction to one in the past.
What to Expect When Starting an ARB
Most people take an ARB once daily, usually in the morning. Blood pressure typically begins to drop within the first one to two weeks, with the full effect becoming apparent after about four weeks. If the initial dose doesn’t bring your blood pressure to target, your doctor may increase it or add a second medication, often a low-dose diuretic.
Because dizziness and lightheadedness are possible early on (especially if you’re starting from very high blood pressure), it helps to stand up slowly and stay hydrated in the first few days. Periodic blood tests to check potassium and kidney function are standard for the first few months and then at regular intervals after that. Most people tolerate ARBs well enough to stay on them long term, which is important because blood pressure control is an ongoing need rather than a short-term fix.