Labetalol’s Mechanism of Action: How Does It Work?

Nearly 50% of adults in the U.S. have high blood pressure (hypertension). This happens when the force of blood pushing against the walls of your blood vessels is too strong. 

Hypertension doesn’t usually cause noticeable symptoms, so many people don’t know they have it. But if left untreated, it can cause major health issues such as heart disease, kidney disease, and even death.

Labetalol is one of several prescription medications that treats high blood pressure. But how exactly does it work to lower blood pressure? We’ll go over labetalol’s mechanism of action and the reasons you may be prescribed it.

What is labetalol?

Labetalol is a beta blocker medication that’s FDA approved to treat hypertension. It’s available in two forms: an oral tablet and an intravenous injection. The injection is only used by healthcare professionals in a hospital or similar setting. Labetalol tablets are only available in generic forms.

Labetalol isn’t a first-choice medication for treating hypertension. Other medication groups — such as angiotensin-converting enzyme (ACE) inhibitors, angiotensin-II receptor blockers (ARBs), and thiazides — are typically tried before beta blockers. But if these medications aren’t enough, beta blockers may be added on. Beta blockers may also be recommended if you have certain heart conditions along with hypertension.

However, labetalol is a first-choice medication for hypertensive emergencies. It’s given intravenously for these situations. A hypertensive emergency is when you have extremely high blood pressure along with organ damage. Labetalol is also a first-choice medication for hypertension in pregnancy.

How does labetalol work?

Labetalol works by blocking certain receptors (binding sites) throughout the body. These are called beta and alpha receptors. 

Some beta blockers mainly block beta receptors in the heart. These are known as cardioselective beta blockers. Others block beta receptors throughout the body, such as the heart, blood vessels, and lungs. These are known as nonselective beta blockers. Labetalol falls into this category. It also blocks alpha receptors. 

Let’s dive into labetalol’s mechanism of action and how it affects each type of receptor below.

EXPERT PICKS: WHAT TO READ NEXT

• Comparing beta blockers: There are several prescription beta blockers available, with similarities and differences to consider.

• Labetalol side effects: Labetalol can cause drowsiness, dizziness, and fatigue, among other side effects.

• Labetalol interactions: If you take labetalol, knowing about its potential medication interactions can help keep you safe.

Labetalol effect on beta-1 receptors

Labetalol blocks beta-1 receptors. These are primarily found in three parts of the body: the heart, kidneys, and fat cells. In the heart, activating beta-1 receptors increases your heart rate and how strongly it contracts. 

By blocking these receptors, labetalol slows your heart rate and makes it easier for your heart to pump blood to the rest of your body. This can lower blood pressure.

Labetalol effect on beta-2 receptors

Labetalol also blocks beta-2 receptors. These are found throughout the body, such as in the blood vessels and muscles in the lungs, heart, and skin.

When beta-2 receptors are activated, your blood vessels dilate (widen) and your heart contracts (tightens). When labetalol blocks these receptors, your blood vessels constrict (tighten) and your heart rate slows.

Constricted blood vessels can make it harder for people with certain lung conditions to breathe, such as those with asthma or chronic obstructive pulmonary disease (COPD). So labetalol may not be the best choice for people with these conditions.

Labetalol effect on alpha-1 receptors

Labetalol is one of the few beta blockers that blocks alpha-1 receptors. When activated, alpha-1 receptors constrict your blood vessels and increase your heart rate. 

When labetalol blocks alpha-1 receptors, your blood vessels dilate and your heart rate slows. This decreases blood pressure. 

Labetalol as an antioxidant

There’s evidence that oxidative stress can negatively affect your heart. Oxidative stress is when there are too many free radicals (unstable molecules that are harmful in large amounts) in the body. There’s some evidence that labetalol may reduce oxidative stress, giving it additional heart benefits. But we need more research on this topic, especially in humans.

Does labetalol start working immediately?

It depends on the form of labetalol you receive. The labetalol injection works almost immediately. The tablets may start working within a few hours. But it typically takes 2 to 3 days for it to start lowering blood pressure.

How do you know if labetalol is working?

You may not have noticeable symptoms of hypertension. So you may not feel differently after taking labetalol. 

But checking your blood pressure at home is a way to see whether labetalol is working for you. Ask your prescriber how often they want you to check it, and what your goal blood pressure reading is.

It can take some time to find the labetalol dose that’s right for you. If your dose is too low, your blood pressure may remain high. As mentioned, you might not have symptoms. Or you may feel headache, dizziness, and fatigue. If your dose is too high, your blood pressure may decrease too much. Symptoms of low blood pressure to watch for include dizziness and weakness. This is common in the first few days after starting labetalol. But if it continues past a few days, or it feels severe, let your prescriber know.

Other labetalol side effects, such as fatigue and nausea, may also be more likely if your labetalol dose is too high. So keep your prescriber updated if you feel differently after starting labetalol.

How does labetalol compare to other blood pressure medications?

As mentioned, labetalol and other beta blockers typically aren’t a first-choice option for treating high blood pressure. Typically, the medications listed below are tried first. These medications are known to be more effective at decreasing blood pressure and preventing long-term health problems compared to beta blockers:

• ACE inhibitors, such as lisinopril (Zestril, Qbrelis)

• Angiotensin II receptor blockers (ARBs), such as losartan (Cozaar)

• Thiazide diuretics, such as hydrochlorothiazide (Microzide)

• Calcium channel blockers, such as amlodipine (Norvasc)

However, beta blockers are a good option in some cases. For example, people with high blood pressure and other heart conditions may benefit from a beta blocker.

Compared to other beta blockers — such as metoprolol (Lopressor, Toprol XL), carvedilol (Coreg), and atenolol (Tenormin) — labetalol is unique in a few ways:

• It blocks alpha-1 receptors (and so does carvedilol). Most other beta blockers only block beta receptors.

• It’s only approved to treat hypertension. Many other beta blockers are approved for other heart conditions.

• It needs to be taken more often (2 to 3 times a day) than most other beta blockers, which can be taken 1 to 2 times a day.

• It’s the beta blocker of choice for hypertensive emergencies or hypertension in pregnancy. But it’s not preferred for most other heart conditions. For example, metoprolol succinate or carvedilol are preferred beta blockers for heart failure.

• It may not be the best option for people with asthma. Other beta blockers like atenolol and metoprolol may be better options since they have less of an effect on blood vessels in the lungs.

Why trust our experts?

Written by:

Alex Brewer, PharmD, MBA

Alex Brewer, PharmD, MBA, is a licensed pharmacist specializing in chronic disease and health and wellness. Upon completing his residency, he worked in the managed care field, conducting medication therapy management and adherence counseling sessions with Medicaid, Medicare, and private insurance patients, before transitioning to a career in medical writing.

Edited by:

Amy B. Gragnolati, PharmD, BCPS

Amy Gragnolati, PharmD, BCPS, is a pharmacy editor for GoodRx. Amy currently holds her pharmacist license in Georgia and California.

Reviewed by:

Ferras Bashqoy, PharmD, BCCCP, BCPPS

Ferras Bashqoy, PharmD, BCCCP, BCPPS, is a clinical pharmacotherapy specialist in the Neonatal Intensive Care Unit (NICU) at Hassenfeld Children’s Hospital in New York City. His favorite part of the job is working with preterm newborns because they are strong and mighty despite their size.

Our editorial standards

Meet our experts