Beta-blockers are a class of medication used to block the effects of stress hormones such as adrenaline on the heart. They’re often prescribed for irregular heartbeats, high blood pressure, and after heart attacks.

Less commonly, beta-blockers may be used to treat:

Doctors typically turn to beta-blockers for high blood pressure when other medications, such as diuretics, aren’t working or have too many side effects. They may be used in combination with other blood pressure-lowering medications, including ACE inhibitors and calcium channel blockers.

Because of the way they work in the body, beta-blockers are also called beta-adrenergic blocking substances.

Different types of beta-blockers work differently. In general, these medications enhance the heart’s ability to relax. Your heart will beat slower and less forcefully when beta-blockers are working. This can help reduce blood pressure and alleviate irregular heart rhythms.

Some beta-blockers only work on the heart itself, while others affect the heart and blood vessels.

Your doctor may prescribe beta-blockers even if you have few symptoms of heart problems or heart failure. These medications can actually improve the heart’s ability to beat.

Commonly prescribed beta-blockers include:

Beta-blockers have been shown to have some health benefits outside of helping the heart. For example, they protect bones by preventing the kidneys from excreting calcium into urine. These drugs block stress hormones that could otherwise cause bone thinning over time.

Beta-blockers aren’t first-line treatment for thinning bones or osteoporosis. Stronger bones just may be an extra benefit of taking these medications.

People with asthma typically shouldn’t take beta-blockers since they can trigger asthma attacks.

Because beta-blockers may affect the control of blood sugar, they’re not usually recommended for people with diabetes.

Side effects of these medications can vary. Many people will experience:

Rarely, you may experience:

If you accidentally take a larger dose than recommended, you may experience:

If you know that an overdose has occurred, call your doctor or local poison control center. The U.S. National Poison Control Center phone number is 800-222-1222.

Some of the older beta-blockers — such as atenolol and metoprolol — have been reported to cause an average weight gain of 2.6 pounds, according to the Mayo Clinic. Fluid retention and accompanying weight gain can be signs that you have heart failure or that your heart failure is getting worse. Be sure to let your doctor know if you gain more than 2 to 3 pounds within a day, gain more than 5 pounds within a week, or your symptoms worsen.

You also may notice some changes in the way your heart works during day-to-day life. For example, beta-blockers prevent spikes in heart rate. You may notice that your heart rate doesn’t climb as high as it normally would during exercise.

Speak with your doctor if you’re concerned about your workouts while taking this medication. They may recommend a stress test to determine your target heart rate during cardio. Stress tests can also help your doctor determine how hard you feel you’re working during a workout. This is known as the rate of perceived exertion.

Beta-blockers are often taken with meals, though they’ll come with special instructions. Take your medication as prescribed. Consult your doctor if you’re having side effects. Don’t stop taking the medication without your doctor’s consent.