Metoprolol is a widely prescribed beta-blocker used to treat a variety of cardiovascular conditions, including high blood pressure (hypertension), chest pain (angina), and heart failure, and to improve survival after a heart attack [1.2.3, 1.6.1]. It works by blocking the effects of the hormone epinephrine (adrenaline), which causes the heart to beat more slowly and with less force, thereby reducing blood pressure [1.5.4]. Metoprolol comes in two main salt forms: metoprolol tartrate (brand name Lopressor) and metoprolol succinate (brand name Toprol-XL) [1.5.3]. While effective, it's important to be aware of its potential side effects.
Common Side Effects
Most mild side effects of metoprolol occur when you first start taking the medication and often lessen as your body adjusts [1.3.2].
- Fatigue and Dizziness: As the medication slows your heart rate and lowers blood pressure, feeling tired or dizzy is one of the most reported side effects [1.3.3]. It's recommended to avoid driving or operating heavy machinery until you know how the medication affects you [1.4.1]. Standing up slowly can help manage dizziness [1.3.2].
- Gastrointestinal Issues: Diarrhea is a common side effect, affecting about 5% of patients [1.5.2]. Nausea, dry mouth, stomach pain, gas, and constipation have also been reported [1.4.2]. Taking the medication with food can sometimes help alleviate stomach upset [1.3.8].
- Depression and Mood Changes: New or worsening feelings of depression can occur [1.3.4]. While research has debated the strength of this link, patients should report any significant mood changes to their doctor [1.3.2].
- Cold Hands and Feet: Metoprolol can affect blood flow to the extremities, leading to a sensation of coldness in the hands and feet [1.3.8].
Serious Side Effects
While less common, some side effects require immediate medical attention. If you experience any of the following, contact your healthcare provider right away [1.4.3].
- Bradycardia (Very Slow Heartbeat): If your heart rate drops too low, it can cause severe dizziness, lightheadedness, confusion, fainting, and fatigue [1.3.5].
- Worsening Heart Failure: Symptoms like shortness of breath (especially when lying down), swelling in the ankles, feet, or hands, and sudden, unusual weight gain can indicate that heart failure is worsening [1.4.3].
- Breathing Problems: Shortness of breath, wheezing, or chest tightness can occur, particularly in individuals with a history of asthma or COPD [1.4.9].
- Severe Allergic Reaction: Though rare, a serious allergic reaction (anaphylaxis) is possible. Symptoms include hives, swelling of the face, lips, tongue, or throat, and difficulty breathing [1.3.5, 1.4.9].
- Masked Hypoglycemia Symptoms: For individuals with diabetes, metoprolol can mask the signs of low blood sugar (hypoglycemia), such as a rapid heartbeat and tremors [1.3.4]. However, sweating as a sign of low blood sugar may still be present [1.3.3].
Metoprolol Tartrate vs. Metoprolol Succinate
The primary difference between these two forms is their release mechanism. Metoprolol tartrate is immediate-release and is typically taken multiple times a day, while metoprolol succinate is an extended-release formula taken once daily [1.5.3]. Their side effect profiles are very similar, though the immediate-release version (tartrate) might cause more fluctuations in drug levels, potentially leading to a higher incidence of certain side effects like bradycardia [1.5.3].
| Feature | Metoprolol Tartrate (Lopressor) | Metoprolol Succinate (Toprol-XL) |
|---|---|---|
| Release | Immediate-Release | Extended-Release [1.5.3] |
| Dosing | Usually twice daily | Once daily [1.5.4] |
| Primary Uses | High blood pressure, post-heart attack | High blood pressure, angina, chronic heart failure [1.5.3] |
| Common Side Effects | Fatigue, dizziness, diarrhea, depression, shortness of breath, slow heart rate, rash [1.5.6] | Fatigue, dizziness, diarrhea, depression, shortness of breath, slow heart rate, rash [1.5.6] |
Important Warnings and Interactions
FDA Black Box Warning: Do not stop taking metoprolol suddenly. Abrupt cessation can lead to severe chest pain, heart attack, or ventricular arrhythmias, especially in patients with coronary artery disease [1.3.9, 1.4.4]. Your doctor will create a plan to gradually reduce the dose over 1 to 2 weeks if you need to stop the medication [1.4.2].
Drug Interactions: Metoprolol can interact with many other drugs. Inform your doctor about all medications you take, including:
- Other blood pressure or heart medications (e.g., calcium channel blockers like diltiazem) [1.6.7].
- Antidepressants like fluoxetine (Prozac) and paroxetine (Paxil), which can increase metoprolol levels [1.6.7].
- Monoamine oxidase inhibitors (MAOIs) [1.6.1].
- Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, which can decrease metoprolol's effectiveness [1.6.5].
- Alcohol can enhance the blood pressure-lowering effect of metoprolol, increasing dizziness [1.6.6].
Medical Conditions: People with certain conditions should use metoprolol with caution or not at all, including those with a very slow heart rate, severe heart block, cardiogenic shock, decompensated heart failure, severe asthma or COPD, or liver disease [1.4.8, 1.3.9].
Conclusion
Metoprolol is a vital medication for managing serious heart conditions, but it carries a risk of side effects. While many common side effects like dizziness and fatigue are mild and manageable, serious effects such as a very slow heartbeat or worsening heart failure symptoms require prompt medical intervention. Always communicate openly with your healthcare provider about any side effects you experience and never stop taking the medication abruptly.
For more detailed information, you can visit the Mayo Clinic's page on Metoprolol.
