ACE inhibitors vs. ARBs: where each acts

Two classes, two points on one pathway

ACE inhibitors and angiotensin II receptor blockers (ARBs) are two families of prescription blood-pressure medications that are often mentioned together. Lisinopril is a commonly cited ACE inhibitor, and losartan is a commonly cited ARB. Both classes act on the same biological pathway — the renin-angiotensin system — but they are understood to intervene at different steps within it. This guide is a direct, mechanism-focused comparison of where each class acts. It is educational only and is not medical advice or a recommendation of one class over another.

In brief, the renin-angiotensin system is a hormone cascade the body uses to help regulate blood pressure and fluid balance. An enzyme called renin starts the sequence, which produces a largely inactive peptide called angiotensin I. Angiotensin-converting enzyme (ACE) then converts angiotensin I into angiotensin II, the peptide generally described as the pathway's principal active signal. Angiotensin II attaches to a receptor known as the angiotensin II type 1 (AT1) receptor, and this binding is understood to promote narrowing of blood vessels and to prompt the release of aldosterone, a hormone associated with sodium and water retention.

The two drug classes are named for the two different points at which they are understood to interrupt this sequence. One class acts on the enzyme that makes angiotensin II; the other acts on the receptor that angiotensin II attaches to. The sections below describe each of those points, and then a difference involving a separate peptide, bradykinin, that further distinguishes the classes.

Where ACE inhibitors act: on angiotensin II production

ACE inhibitors, the class that includes lisinopril, are named for the enzyme they are designed to inhibit — angiotensin-converting enzyme. This enzyme sits partway along the pathway, at the step where angiotensin I is converted into angiotensin II. By occupying the enzyme, an ACE inhibitor is understood to slow that conversion, so that less angiotensin II is formed in the first place.

Because the intervention happens upstream, at the production step, the downstream signals attributed to angiotensin II — the narrowing of blood vessels and the release of aldosterone — are understood to be diminished simply because there is less of the peptide available to send them. Lisinopril is a long-established generic ACE inhibitor, and reference materials describe it as being eliminated largely unchanged by the kidneys. Whether the class is appropriate for a given person, and at what dose, is a decision an independent licensed provider makes based on that person's medical history.

Where ARBs act: on the receptor

ARBs, the class that includes losartan, act one step further along the same pathway. Rather than reducing how much angiotensin II the body makes, an ARB is designed to bind the AT1 receptor — the docking site where angiotensin II would otherwise attach. By occupying that receptor, an ARB is understood to block angiotensin II from delivering its signal, regardless of how much of the peptide is circulating.

The distinction is one of placement. An ACE inhibitor is understood to act on the supply of angiotensin II; an ARB is understood to act on the receptor that receives it. Because an ARB acts at the receptor, its mechanism does not depend on how the peptide was produced — a point that also relates to the fact that angiotensin II can be generated through routes other than ACE. Losartan is a long-established generic ARB. As with the other class, whether it is appropriate for an individual is a clinical judgment reserved for an independent licensed provider.

The bradykinin difference

ARBs act at the AT1 receptor and do not inhibit angiotensin-converting enzyme, so they are not associated with the same bradykinin buildup, and the dry cough linked to ACE inhibitors is described as less common with ARBs. This mechanistic difference is one reason a provider may consider an ARB for a person who did not tolerate an ACE inhibitor — but that is a clinical judgment for the provider, not a conclusion an article can draw for any individual.

What these medications are

Lisinopril and losartan are prescription blood-pressure medications, categorized as antihypertensive agents — the group of medications a clinician may consider as part of blood-pressure management, alongside lifestyle measures and other treatments a provider might recommend. In the United States, both are dispensed only with a valid prescription from a licensed provider.

Because both classes act on the renin-angiotensin system, reference materials describe several situations that call for caution and provider oversight. For example, ACE inhibitors and ARBs are both generally described as not appropriate during pregnancy, and providers commonly monitor kidney function and blood potassium in people taking either class. These are descriptive class characteristics rather than instructions; whether any of them applies to a given individual is determined during a medical evaluation, not by an article.

How it works on OpenDoseRx

On OpenDoseRx, a licensed clinician — not the shopper — makes the medical decision. You choose a product and strength, then complete a medical intake with your health history. An independent, licensed U.S. provider reviews that intake and decides whether a prescription is appropriate for you.

If it is, a licensed U.S. pharmacy prepares and ships it; if the provider declines, you are not charged for the medication and receive a full refund. This article is educational only and is not a substitute for a conversation with your own healthcare provider.