Is Metoprolol a Beta Blocker or ACE Inhibitor?

Metoprolol is a beta blocker. It is not an ACE inhibitor. The confusion is understandable because both drug classes treat overlapping conditions like high blood pressure and heart failure, and a patient may even take both at the same time. But the two work through entirely different mechanisms, carry different side-effect profiles, and are not interchangeable.

How Beta Blockers and ACE Inhibitors Differ

The simplest way to keep these apart is to think about what each one blocks. Beta blockers target beta-adrenergic receptors on the heart and blood vessels. When your body releases adrenaline and related stress hormones, these receptors tell the heart to beat faster and harder. A beta blocker sits on those receptors and dampens the signal, slowing the heart rate and reducing the force of each beat. That lowers blood pressure primarily by reducing how much blood the heart pumps per minute.

ACE inhibitors work on a completely different system. ACE stands for angiotensin-converting enzyme, a protein that converts an inactive molecule called angiotensin I into angiotensin II, a powerful chemical that constricts blood vessels. By blocking that conversion, ACE inhibitors cause blood vessels to relax and widen, which drops blood pressure through reduced vascular resistance rather than reduced heart output.¹ ACE inhibitors also slow the breakdown of bradykinin, a peptide that helps blood vessels dilate. That secondary action is responsible for some of their benefits and, as we’ll see, one of their most recognizable side effects.

Metoprolol is classified as a “cardioselective” beta blocker, meaning it preferentially blocks beta-1 receptors concentrated in the heart rather than beta-2 receptors found in the lungs and elsewhere. That selectivity matters because blocking beta-2 receptors can tighten the airways, a real problem for people with asthma or lung disease. Cardioselective agents like metoprolol are generally better tolerated in those populations, though caution is still warranted.²

What Metoprolol Is Prescribed For

Metoprolol is one of the most commonly prescribed beta blockers in the world, with uses spanning several cardiovascular conditions. Its core indications include high blood pressure, chest pain from coronary artery disease, certain types of irregular heartbeat, and heart failure with reduced pumping ability.

The evidence for metoprolol in heart failure is especially strong. A large randomized trial found that the extended-release form reduced total mortality and hospitalizations by about 19% compared to placebo, and cut hospitalizations specifically due to worsening heart failure by roughly 31%.³ That trial was a turning point in how doctors thought about beta blockers and heart failure, since the intuitive concern had always been that slowing an already-struggling heart would make things worse. It turns out the opposite is true: reducing the constant adrenaline bombardment lets the heart recover.

In heart attacks, early use of intravenous metoprolol before a procedure to reopen the blocked artery has been linked to better preservation of heart muscle function, with fewer patients showing severely depressed heart function at one week and six months afterward.⁴ Research also suggests metoprolol can reduce the harmful remodeling and scarring that occurs in the heart after blood flow is cut off.⁵

ACE inhibitors have their own overlapping set of uses. They treat the same conditions of hypertension and heart failure, and are also used after heart attacks and for kidney protection in people with diabetes.⁶ The overlap in indications is the main reason people mix up the two classes. A doctor may switch a patient from one to the other, or prescribe both together, creating the impression that they are similar medications when they are mechanistically quite different.

Metoprolol Tartrate Versus Metoprolol Succinate

If you look at your prescription bottle, you’ll see one of two salt forms listed: metoprolol tartrate or metoprolol succinate. They contain the same active drug, but they’re formulated differently and are not simply swapped one-for-one.

Metoprolol tartrate is the immediate-release version. It gets absorbed quickly, reaches peak blood levels within a couple of hours, and is typically taken twice a day. Metoprolol succinate is an extended-release formulation designed to release the drug steadily over about 20 hours, allowing once-daily dosing.⁷ After you swallow the succinate tablet, it breaks apart into tiny individual pellets, each one acting as its own slow-release unit. The result is much more even drug levels throughout the day, with lower peaks and higher troughs compared to the twice-daily tartrate version.⁸

This distinction matters clinically. The landmark heart failure trial that showed mortality benefits used the extended-release succinate form specifically.⁹ For hypertension or simple rate control, either form may be appropriate, but for heart failure, prescribers generally stick with the succinate version. A 100-mg extended-release tablet contains about 95 mg of metoprolol succinate and is considered equivalent in activity to a 100-mg dose of metoprolol tartrate.⁷

Side Effects You’d Expect From Each Class

One practical reason to know which class your medication belongs to is that the side effects are quite different. If you’re on metoprolol and experiencing a particular symptom, knowing it’s a beta blocker helps you and your doctor figure out whether the drug could be the cause.

Beta blockers like metoprolol can produce side effects tied to their core action of dampening adrenaline’s effects. These include a slow heart rate, fatigue, cold hands and feet, dizziness, and occasionally depression or vivid dreams.² An analysis of over 16,000 adverse event reports from the FDA’s reporting system flagged some less commonly discussed signals with metoprolol, including orthostatic intolerance, where standing up causes an exaggerated drop in blood pressure.¹⁰ Your genetic makeup can also influence how you metabolize metoprolol. The enzyme CYP2D6, which breaks down the drug in the liver, varies widely between individuals. People who metabolize it slowly end up with higher blood levels at the same dose, which can increase the likelihood of side effects including cardiovascular symptoms and central nervous system complaints.¹¹

ACE inhibitors carry a signature side effect that beta blockers do not: a persistent, dry cough. It develops in roughly 5% to 35% of people who take them, caused by the buildup of bradykinin that the drug prevents from being broken down.¹² Because the cough is a class effect of all ACE inhibitors, switching from one ACE inhibitor to another doesn’t help. The more concerning ACE-inhibitor reaction is angioedema, a swelling of the lips, tongue, or throat that occurs in up to about 0.7% of patients and can be life-threatening.¹³ Neither the cough nor the angioedema occurs with metoprolol, because it doesn’t touch the bradykinin pathway at all. If your blood pressure medication is giving you a nagging cough, it’s almost certainly not a beta blocker causing it.

Why Doctors Sometimes Prescribe Both Together

Rather than choosing between a beta blocker and an ACE inhibitor, many patients end up on both. This is especially common after a heart attack or in chronic heart failure, where guidelines recommend layering multiple medications that attack the problem from different angles.

The logic is straightforward: a beta blocker like metoprolol slows the heart and reduces its oxygen demand by blocking the sympathetic nervous system’s drive, while an ACE inhibitor relaxes blood vessels and reduces the workload the heart has to pump against.¹⁴ Together, they provide what researchers call comprehensive neuroendocrine blockade, hitting both of the major hormonal systems that drive harmful heart remodeling. Animal research has shown that combining the two after a heart attack yields improvements in heart energy metabolism and pumping function beyond what either drug achieves alone.¹⁵

If you’re taking both, it helps to understand that each is doing something the other cannot. The beta blocker is calming the heart directly; the ACE inhibitor is loosening up the plumbing. Knowing that can make it easier to keep track of why you’re on each medication, and why stopping one doesn’t necessarily mean you can also stop the other.

Kidney Protection and the ACE Inhibitor Advantage

One area where ACE inhibitors have a clear edge over beta blockers is kidney protection, particularly in people with diabetes or protein in their urine. ACE inhibitors dilate the small blood vessel leaving the kidney’s filtering units, which reduces the pressure inside those filters and slows damage over time. Beta blockers don’t offer that same targeted kidney benefit.

In kidney transplant recipients, a study comparing the ACE inhibitor quinapril to the beta blocker atenolol found that both controlled blood pressure equally well, but quinapril reduced albumin loss in the urine while atenolol did not. The researchers interpreted the drop in albuminuria as a sign that the ACE inhibitor may help preserve long-term graft function.¹⁶ When looking at broader populations with high blood pressure, however, a larger study found no statistically significant difference in kidney disease outcomes between patients started on an ACE inhibitor versus a beta blocker as second-line therapy.¹⁷ So the kidney advantage of ACE inhibitors appears most pronounced in people who already have kidney damage or are losing protein in their urine, rather than in the general hypertension population.

Metoprolol and Blood Sugar

A longstanding concern with beta blockers is that they can mask the symptoms of low blood sugar in people with diabetes. Adrenaline normally triggers a fast heart rate, trembling, and anxiety when blood sugar drops too far, and blocking that adrenaline signal could theoretically leave a person unaware of a dangerous low. The concern is real for older, non-selective beta blockers, but metoprolol’s selectivity for the heart’s beta-1 receptors makes the picture more reassuring.

Research in insulin-dependent diabetics found that metoprolol did not significantly alter blood glucose levels during prolonged low blood sugar. Their bodies still mounted a robust counter-regulatory hormone response, including increased epinephrine, norepinephrine, growth hormone, and cortisol. Sweating, one of the key warning symptoms of a low, was actually increased by metoprolol.¹⁸ Another study confirmed that metoprolol did not counteract the early hormonal defense against falling blood sugar and did not mask the clinical signs of a low.¹⁹ This is good news if you have diabetes and your doctor recommends metoprolol for a heart condition, though blood sugar monitoring remains important whenever a beta blocker is part of the regimen.

Why You Should Never Stop Metoprolol Abruptly

One critical piece of knowledge for anyone on metoprolol: do not stop it suddenly. When you take a beta blocker regularly, your body compensates by becoming more sensitive to adrenaline. If you abruptly remove the blocking drug, that heightened sensitivity is unmasked all at once.

A study of patients taking 300 mg of metoprolol daily found that abrupt withdrawal produced an average 52% rebound increase in the heart’s sensitivity to stimulation, along with a 15% rise in resting heart rate within two to eight days.²⁰ A larger study of patients who had metoprolol gradually tapered over one week still found significantly more cardiac symptoms and mental symptoms in the metoprolol group than in those withdrawing from placebo. About one in four patients in the metoprolol group needed to restart the medication because withdrawal symptoms became disabling.²¹ The practical takeaway is that any dose change should be done slowly and under medical supervision.

ACE inhibitors, by contrast, do not produce the same kind of withdrawal rebound. You should still consult your doctor before stopping any blood pressure medication, but the abrupt-withdrawal risk is a distinctly beta-blocker phenomenon.

Pregnancy and Drug Class Matters

Perhaps the starkest clinical difference between these two drug classes shows up in pregnancy. ACE inhibitors are considered teratogenic, meaning they can cause birth defects and serious harm to a developing fetus. They are contraindicated in pregnancy and should be stopped as soon as a pregnancy is confirmed or planned.²²

Beta blockers, including metoprolol, are considered relatively safe and can be used effectively during pregnancy when blood pressure control or heart rate management is needed. Metoprolol is in fact one of the preferred options when a pregnant woman requires treatment for hypertension or certain heart rhythm problems. This is a situation where knowing which class your medication belongs to could have immediate, serious consequences. A woman taking an ACE inhibitor who becomes pregnant needs to switch medications promptly; a woman on metoprolol generally does not face the same urgency.

What Happens in Overdose

Beta-blocker overdose and ACE-inhibitor overdose look nothing alike, which is another reason the distinction matters in an emergency. Taking too much metoprolol exaggerates its core pharmacological effects: the heart slows dangerously, blood pressure plummets, and the patient can become critically unstable. The hallmark of severe beta-blocker poisoning is profound bradycardia and hypotension that does not respond easily to standard resuscitation measures. High-dose glucagon is considered the first-line antidote because it stimulates the heart through a pathway that bypasses the blocked beta receptors entirely.²³

ACE-inhibitor overdose, while serious, typically presents mainly as severe low blood pressure without the dangerous heart-slowing component. The treatment approach is different, centered on fluid resuscitation and blood pressure support rather than the glucagon protocol used for beta-blocker toxicity. Emergency physicians need to know which drug class was involved to choose the right treatment, which is one more reason it’s worth keeping straight in your own mind too.

The Broader Beta-Blocker Family

Metoprolol is just one member of a large family of beta blockers that emerged after Sir James Black developed propranolol in the 1960s while working at a pharmaceutical company. Black was motivated by his father’s death from a heart attack and wanted to find a way to protect the heart from adrenaline’s damaging effects.²⁴ Propranolol was the first widely used beta blocker and blocked both beta-1 and beta-2 receptors equally. Later drugs like metoprolol were engineered to be more selective for the heart’s beta-1 receptors, reducing unwanted effects on the lungs and metabolism.

Other cardioselective beta blockers you might encounter include atenolol and bisoprolol. Non-selective beta blockers like carvedilol and labetalol block both receptor types and are sometimes chosen deliberately for that broader action. Carvedilol, for example, is another beta blocker with strong evidence in heart failure but works through a slightly different receptor profile than metoprolol. Each has trade-offs, and the choice between them depends on the specific condition being treated and the individual patient’s other health issues. What none of them share is any overlap with ACE inhibitor pharmacology. They are all beta blockers, full stop.