Angiotensin receptor blockers (ARBs) lower blood pressure by blocking a specific chemical signal that tells your blood vessels to tighten. They target a hormone called angiotensin II, one of the most powerful blood-vessel-constricting substances your body produces. By preventing this hormone from doing its job, ARBs allow blood vessels to relax and widen, reducing the force your heart has to pump against.
The Hormone System ARBs Target
Your body has a built-in pressure regulation system called the renin-angiotensin system. When your kidneys detect low blood flow or low sodium, they release an enzyme called renin. Renin kicks off a chain reaction that ultimately produces angiotensin II, a hormone with several powerful effects: it constricts blood vessels, signals your adrenal glands to release aldosterone (which makes your kidneys hold onto sodium and water), and stimulates thirst. All of these actions raise blood pressure. In healthy people, this system activates when needed and then quiets down. In people with high blood pressure, heart failure, or kidney disease, the system can be chronically overactive.
How ARBs Block the Signal
Angiotensin II does its work by latching onto docking sites on cells called AT1 receptors. These receptors sit on the walls of blood vessels, in the kidneys, in the heart, and in the adrenal glands. When angiotensin II binds to an AT1 receptor, it triggers vessel constriction, sodium retention, and tissue remodeling that can thicken the heart muscle over time.
ARBs work by sitting in that same docking site and physically blocking angiotensin II from attaching. The hormone is still produced, but it can’t activate the receptor. This means blood vessels stay relaxed, your kidneys release more sodium and water instead of holding onto them, and aldosterone secretion drops. The net result is lower blood pressure and less strain on the heart and kidneys.
There’s a second type of angiotensin receptor, called AT2, that ARBs leave alone. AT2 receptors appear to have some protective effects on tissues, including promoting blood vessel relaxation and reducing inflammation. Because ARBs only block AT1 while leaving AT2 available, the angiotensin II that’s still circulating can bind to AT2 receptors instead, potentially adding a modest beneficial effect.
How ARBs Differ From ACE Inhibitors
ACE inhibitors (like lisinopril and enalapril) attack the same hormone system but at an earlier step. They block the enzyme that converts angiotensin I into angiotensin II, so less of the hormone gets made in the first place. That enzyme also breaks down a substance called bradykinin, which is a natural vasodilator. When ACE inhibitors prevent bradykinin from being broken down, extra bradykinin accumulates in the lungs and irritates the airways. This is what causes the persistent dry cough that affects a significant number of people on ACE inhibitors.
ARBs don’t interfere with bradykinin at all. They let angiotensin II get produced normally but block it from working at the receptor. Because bradykinin metabolism is unaffected, the nagging cough and the rarer but more serious swelling reaction (angioedema) are far less common with ARBs. This is the main reason people who can’t tolerate an ACE inhibitor are often switched to an ARB.
How Quickly They Work
Most ARBs reach their peak blood pressure effect about 3 to 6 hours after you take a dose. How long each dose lasts depends on the specific medication. Losartan has a relatively short half-life of about 2 hours, though its body converts it into an active byproduct that lasts 6 to 9 hours. Irbesartan and olmesartan last longer, with half-lives of 11 to 15 hours and 12 to 14 hours respectively. Telmisartan is the longest-acting ARB on the market, with a half-life of roughly 24 hours, meaning a single daily dose provides steady coverage.
Full blood pressure reduction typically takes a few weeks of consistent use, even though each individual dose starts working within hours. Your prescriber may adjust the dose after 2 to 4 weeks based on how your blood pressure responds.
Conditions ARBs Treat
The 2025 guidelines from the American Heart Association and American College of Cardiology list ARBs as one of four first-line medication classes for treating high blood pressure, alongside thiazide diuretics, calcium channel blockers, and ACE inhibitors. They’re often combined with a diuretic or calcium channel blocker as initial therapy when a single drug isn’t enough.
Beyond blood pressure, ARBs are used for several related conditions:
- Heart failure: Valsartan is commonly prescribed to reduce cardiovascular death in patients with reduced heart function, particularly after a heart attack that has weakened the left ventricle.
- Diabetic kidney disease: Losartan is approved to slow the progression of kidney damage in people with type 2 diabetes and protein in their urine. By lowering pressure inside the kidney’s filtering units, ARBs help protect them from further damage.
- Chronic kidney disease: Current guidelines recommend an ACE inhibitor or ARB as the first choice for people with CKD who have significant protein leaking into their urine, based on robust evidence of long-term kidney and cardiovascular benefits.
- Stroke prevention: Losartan is approved to reduce stroke risk in people with high blood pressure and thickening of the heart’s left ventricle.
Common ARB Medications
Eight ARBs are available, and they all share the same basic mechanism. The differences come down to how long they last, how they’re metabolized, and which conditions they’re specifically approved for. The most widely prescribed include losartan, valsartan, irbesartan, olmesartan, candesartan, telmisartan, eprosartan, and azilsartan. All are taken by mouth, and most are dosed once daily. Valsartan for heart failure is an exception, typically taken twice a day.
Side Effects and Risks
ARBs are generally well tolerated compared to many blood pressure medications. Because they don’t affect bradykinin, the cough and swelling reactions linked to ACE inhibitors are rare. The most notable risks involve potassium levels and kidney function.
By reducing aldosterone (the hormone that tells your kidneys to excrete potassium), ARBs can cause potassium to build up in the blood. This happens in fewer than 2% of people overall, and potassium levels typically rise by only a small amount. However, the risk climbs significantly in people who already have impaired kidney function. Elevated potassium can cause dangerous heart rhythm problems, so periodic blood tests are standard when starting an ARB, especially if you have kidney disease or take other medications that raise potassium.
Other possible side effects include dizziness (from the blood pressure drop), fatigue, and occasionally elevated creatinine levels reflecting changes in kidney blood flow. ARBs are not safe during pregnancy, as they can cause serious harm to a developing fetus, particularly in the second and third trimesters.