Lopressor (metoprolol tartrate) is a prescription drug that’s used for certain heart-related conditions, including high blood pressure. Lopressor can cause side effects that range from mild to serious. Examples include fatigue (low energy) and dizziness.

Lopressor is used in adults to:

The active ingredient in Lopressor is metoprolol tartrate. (An active ingredient is what makes a drug work.) The drug comes as a tablet.

Keep reading to learn about the common, mild, and serious side effects that Lopressor can cause. For a general overview of the drug, including details about its uses, see this article.

Below are just a few of the more common side effects reported by people who took Lopressor in studies. These side effects can vary depending on which condition you’re taking the drug to treat.

More common side effects in people taking Lopressor for high blood pressure and stable angina include:

More common side effects in people taking Lopressor for heart attack include:

* To learn more about this side effect, see the “Side effects explained” section below.

Mild side effects have been reported with Lopressor. These side effects can vary depending on which condition you’re taking the drug to treat.

Side effects of Lopressor include:

* To learn more about this side effect, see the “Side effects explained” section below.
† An allergic reaction is possible after using Lopressor. But it’s not clear whether this side effect occurred in studies.

In most cases, these side effects should be temporary. And some may be easily managed. But if you have any symptoms that are ongoing or bother you, talk with your doctor or pharmacist. And do not stop taking Lopressor unless your doctor recommends it.

Lopressor may cause mild side effects other than the ones listed above. See the drug’s prescribing information for details.

People taking Lopressor in studies have reported serious side effects. However, these side effects were rare.

Serious side effects have been reported with Lopressor. These include:

If you develop serious side effects while taking Lopressor, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

* To learn more about this side effect, see the “Side effects explained” section below.
† An allergic reaction is possible after using Lopressor. But it’s not clear whether this side effect occurred in studies.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Lopressor, visit MedWatch.

Get answers to some frequently asked questions about Lopressor’s side effects.

Does Lopressor come in a 25-mg strength? If so, will that strength cause fewer side effects?

No, Lopressor doesn’t come in a 25-mg strength. However, Lopressor tablets come in a 50-mg tablet that’s scored. This means you can split it in half if your dose is 25 mg. A lower dose of Lopressor is not expected to cause different side effects.

How do side effects of Lopressor in older adults compare with those seen in younger adults?

Side effects of Lopressor in older adults (65 years and over) are expected to be the same as in younger adults. Studies of Lopressor did not show any change in side effects based on age.

But some older adults may have an increased risk of certain side effects of Lopressor. Examples may include dizziness or tiredness. It’s also more likely for older adults to have other conditions or to be taking other medications that could increase the risk of side effects with Lopressor.

If you’re age 65 years or older, doctors will likely prescribe a lower dosage of Lopressor than usual. And they may increase your dosage depending on how your body responds to treatment. Talk with your doctor if you’re concerned about side effects of Lopressor due to your age.

Does Lopressor cause weight gain?

It’s not likely. People taking Lopressor in studies did not report weight gain. After the drug came onto the market, there have been rare reports of people gaining weight during Lopressor treatment. But it’s not clear whether Lopressor was the cause of weight gain in those cases.

If you’re concerned about weight gain while taking Lopressor, talk with your doctor.

How long does Lopressor stay in your system?

Lopressor stays in your system for about 1–2 days after your last dose. Lopressor has an approximate half-life of 3–7 hours. (This is the amount of time it takes for your body to remove half a dose of Lopressor from your system.)

If you experience any side effects while taking Lopressor, they’ll likely go away once you stop taking the drug. But if symptoms keep bothering you after stopping Lopressor, talk with your doctor.

Learn more about some of the side effects Lopressor may cause.

Fatigue

Some people taking Lopressor may experience fatigue (low energy). This was a common side effect in people who took Lopressor in studies. Fatigue can make you feel more tired than usual when doing your regular activities.

What might help

If you experience fatigue, you can help manage it by drinking enough water, exercising regularly, and eating a balanced diet.

Dizziness

Dizziness can occur while taking Lopressor. This was a common side effect in people taking Lopressor in studies.

What might help

If you experience dizziness, be careful when changing positions, such as going from sitting to standing. If you start to feel dizzy, you should sit or lie down and wait for the dizziness to pass to help prevent falls.

Diarrhea

Lopressor may cause diarrhea in some people. This was a common side effect reported in people who took Lopressor in studies.

In most cases, diarrhea from Lopressor is likely to be mild.

What might help

If you experience diarrhea, you should drink plenty of fluids. This is because diarrhea can cause dehydration. If you have diarrhea that seems severe or does not go away, talk with your doctor. They may recommend that you use an over-the-counter medication such as Imodium (loperamide).

Slow heart rate

Lopressor may cause slow heart rate. This was a common side effect in people who took Lopressor in studies. In some cases, this side effect can be serious. A slow heart rate can cause you to feel tired or faint.

What might help

If you think you’re experiencing a slow heart rate, talk with your doctor. They’ll likely monitor your heart rate and can determine whether they should lower your Lopressor dosage or if you should switch to a different treatment.

Allergic reaction

Like most drugs, Lopressor can cause an allergic reaction in some people. Mild allergic reactions were reported in studies, but it’s unclear whether severe allergic reactions occurred.

Symptoms can be mild to serious and can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)
  • swelling under your skin, usually in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms. Examples include:

  • an antihistamine you swallow, such as Benadryl (diphenhydramine)
  • a product you apply to your skin, such as hydrocortisone cream

If your doctor confirms you’ve had a mild allergic reaction to Lopressor, they’ll decide if you should continue taking it.

If you have symptoms of a severe allergic reaction, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you’ve had a serious allergic reaction to Lopressor, they may have you switch to a different treatment.

Keeping track of side effects

During your Lopressor treatment, consider taking notes on any side effects you’re having. You can then share this information with your doctor. This is especially helpful when you first start taking a new drug or using a combination of treatments.

Your side effect notes can include things such as:

  • what dose of the drug you were taking when you had the side effect
  • how soon you had the side effect after starting that dose
  • what your symptoms were
  • how your symptoms affected your daily activities
  • what other medications you were taking
  • any other information you feel is important

Keeping notes and sharing them with your doctor will help them learn more about how Lopressor affects you. They can then use this information to adjust your treatment plan if needed.

Below is important information you should consider before taking Lopressor.

Lopressor can sometimes cause harmful effects in people who have certain medical conditions. This is known as a drug-condition interaction. Other factors may also affect whether Lopressor is a good treatment option for you.

Talk with your doctor about your health history before starting Lopressor. Be sure to tell them if any of the following factors apply to you:

Heart problems. Beta-blockers such as Lopressor can cause heart problems, such as a slow heart rate and worsening heart failure. If you have had any heart problems, tell your doctor before starting Lopressor. If you have had certain conditions such as heart block, you should not take Lopressor. If you have new or worsening heart problems while taking Lopressor, your doctor may lower your dose or suggest a different medication.

Diabetes. Lopressor can hide the symptoms of low blood sugar. Due to this risk, if you have diabetes, your doctor will help you monitor your blood sugar while taking Lopressor.

Overactive thyroid. Lopressor can hide the symptoms of an overactive thyroid. Due to this risk, if you have hyperthyroidism, your doctor will help you monitor your thyroid function while taking Lopressor.

Certain heart problems when suddenly stopping Lopressor. If you have coronary artery disease (CAD) and you suddenly stop taking Lopressor, you may experience certain heart problems. Examples may include a heart attack or worsening chest pain. This risk may be higher in people with ischemic heart disease (damage to your heart caused by reduced blood flow). (CAD is a type of ischemic heart disease.) Talk with your doctor if you’re interested in stopping Lopressor treatment. You should never adjust your treatment plan on your own.

Allergic reaction. If you’ve had an allergic reaction to Lopressor or any of its ingredients, your doctor will likely not prescribe Lopressor. Ask them what other medications are better options for you.

Alcohol and Lopressor

There is no known interaction between Lopressor and alcohol.

If you drink alcohol, talk with your doctor about how much alcohol may be safe to consume with your condition and treatment plan.

Pregnancy and breastfeeding while taking Lopressor

It’s not known if Lopressor is safe to use during pregnancy.

It’s also unknown if the drug is safe to take while breastfeeding. Lopressor passes into breast milk in small quantities. But it’s not known what effects (if any) this may have on a child who’s breastfed.

If you’re pregnant or breastfeeding, or planning to become pregnant or to breastfeed, talk with your doctor before taking Lopressor.

If you still have questions about side effects that Lopressor can cause, talk with your doctor. Examples of questions you may want to ask include:

  • Will my risk of side effects change if my Lopressor dose is adjusted?
  • How do the side effects of Lopressor compare with those of other drugs that can treat my condition?
  • What should I do if I experience side effects from Lopressor?

To learn more about Lopressor, see these articles:

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Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.