Metoprolol (pronounced me-TOE-pro-lol or MET-oh-PROE-lol) is a beta-adrenergic blocking drug, meaning it blocks the action of the sympathetic nervous system by blocking beta 1 receptors on sympathetic nerves (beta 1 type of receptors are found in the heart and blood vessels). The sympathetic nervous system is primarily responsible for increasing heart rate, so by blocking this action, metoprolol can reduce heart rate, treat angina (chest pains) and hypersensitivity (high blood pressure).
As with any medication that works with the heart, it is important to take this drug only as directed to reduce the risk of adverse metoprolol side effects.
Metoprolol can lower blood pressure by reducing the force of contraction of the heart muscle, which in turn reduces the heart muscle’s need for oxygen. Angina pectoris, or heart pain, is usually caused by a lack of oxygen in the heart muscle or when the muscle’s demand outweighs the supply.
Due to its ability to affect blood flow through arteries and veins, metoprolol is useful in treating rapid heart rhythms, hypertension, coronary artery disease (CAD), angina pectoris, acute myocardial infarction, supraventricular tachycardia, cardialgia, vasovagal syncope, ventricular tachycardia, congestive heart failure and prevention of migraine headaches, along with other uses.
Brand names for metoprolol include Lopressor and Toprol-XL (USA); Minax and Metrol (Australia); Corvitol (Germany); Metxl, Metolar and Starpress,Restopress (India); Selokeen (Netherlands); Betaloc and Bloxan (Slovenia); Presolol (Serbia); and Neobloc (Israel). Multiple generic products are available as well.
Extensive studies in pregnant women and children have yet to be conducted, so the severity of metoprolol side effects in these groups is unknown. It is known that metoprolol can pass through breast milk and affect infants, so women who are breast-feeding should consult their doctor before taking metoprolol.
Common Side Effects
There are many common metoprolol side effects that may be infrequent or insignificant and not require treatment. With any side effects, consult a doctor and discuss the available options, such as lowering the dose of medication, switching medication, ending medication or treating side effects with a supplemental medication. Because metoprolol treats symptoms that can lead to heart attacks, a doctor may consider the presence of side effects as an acceptable risk compared to the risk of taking no medication at all.
Common metoprolol side effects are numerous and can include:
- joint pain
- muscle pain
- body cramps
- short-term memory loss
- fainting spells
- ataxia (lack of coordination)
- shortness of breath
- flu symptoms
- dry mouth
- stomach pain
- eye pain
- rash and insomnia.
Impaired thinking or reaction is a common metoprolol side effect, so don’t drive, operate heavy machinery or do any heavy lifting until you know how the drug affects you.
Less common metoprolol side effects
Less common metoprolol side effects may include: hepatitis; worsening of psoriasis; red, blistered or peeling skin; reversible hair loss; photosensitivity; arthritis; weight gain; diabetes mellitus; anorexia; impotence; Peyronie’s disease (curvature of the penis) and palpitations. These side effects occur in less than 1 percent of people who take the drug. Because these side effects are rare, it has yet to be proven that they occurred as a direct result of the medication or due to other contributing factors.
Severe metoprolol side effects
Serious side effects can occur while take metoprolol that require immediate medical attention. Severe metoprolol side effects can include:
- sudden weight gain
- hypotension (low blood pressure)
- arrhythmia (irregular heartbeat)
- variant angina pectoris (spasms in the coronary artery)
- congestive heart failure
- severe respiratory distress
- bowel obstruction
- severe depression up to catatonia
- unusual bleeding or bruising
- unexplained swelling in the arms, legs, hands or feet.
Allergic reactions can appear as metoprolol side effects and may include difficulty breathing; hives; and swelling of the face, lips, tongue or throat. Patients with lung diseases such as chronic bronchitis, asthma or emphysema may see increased difficulties in breathing while taking metoprolol.
Severe side effects can occur when mixing metoprolol with other medications. Do not take metoprolol if you are taking antidepressants; heart medication; anti-malaria medications; MAO inhibitors; diabetes medication; medicine for asthma; diuretics; cold medicines; diet pills; digoxin; clonidine; ritonavir; or terbinafine. Other drugs and medications (including vitamins, minerals and herbal products) may affect the way metoprolol works in your body and could cause other side effects.
Metoprolol withdrawal symptoms
As with many medications, you should discuss discontinuing metoprolol with a doctor, as stopping the medication suddenly can cause severe side effects or cause conditions to worsen. A doctor may decrease dosing gradually over time if it is decided to end taking metoprolol.
While in the process of stopping medication, it is recommended to limit physical activity and exertion to decrease strain on the heart. Seek emergency medical attention if you experience chest pressure or pain; unusual sweating; or an irregular heartbeat.
Patients suffering from withdrawal may experience:
- chest pain
- troubled breathing
- excessive sweating
- tightness in the chest
- Those with angina pectoris who stop taking metoprolol could seriously aggravate their angina symptoms.
Metoprolol may affect test results
Metoprolol side effects may also include changes seen in blood tests. Biochemical abnormalities such as increased liver enzymes, dyslipidemia (high cholesterol/fat in the blood) and significantly decreased high-density lipoproteins (HDL) may be caused by taking metoprolol.
Metoprolol may also lead to low blood sugar levels (hypoglycemia), low blood sodium levels and increased level of the serum potassium (hyperkalemia). The drug can also cause hormonal tests to show a decrease in free and total testosterone.
Discuss with your doctor any changes in blood tests or laboratory tests that may occur while taking metoprolol. It is possible for metoprolol to affect other tests as well, so make sure your doctor is aware that you are taking the medication.
Metoprolol Side Effects: Dosing and possible overdosing
Metoprolol is typically taken before meals and at bedtime and is available in 25 mg, 50 mg, 100 mg and 200 mg extended releases doses as well as in 25 mg, 50 mg and 100 mg immediate release doses.
Total doses for treating angina rage from 100 mg to 400 mg daily in two separate intakes. Hypertension treatment doses range from 100 mg to 450 mg total each day in either a single or divided dose. Three 5-mg injections are used to treat acute myocardial infarction and must be administered 2 minutes apart and followed by 50 mg oral metoprolol every 6 hours for a total of 48 hours. After 48 hours, patients usually receive 100 mg twice a day orally for an extended period.
If a dose is missed, take the dose as soon as you realize it was not taken. However, if the discovery comes close to a scheduled dose, do not take an additional dose. Doubling up on doses can lead to overdosing, which can have severe consequences.
Immediately contact a poison control center or emergency room if an overdose is suspected. Symptoms of an overdose vary but can include: very slow heartbeat, severe weakness, fainting, severe dizziness, and trouble breathing. U.S. residents can call the U.S. National Poison Hotline at 1-800-222-1222. Canadian residents should call their provincial poison control center, which can be found at www.capcc.ca/provcentres/centres.html.
Metoprolol side effects can vary depending on the patient and other factors such as medical history, allergies and combinations of medications. It is best to talk with a healthcare provider to discuss advantages or disadvantages of starting any drug regimen. Consult your doctor if any side effects occur. Metoprolol side effects may be reported to the FDA in the United States at 1-800-FDA-1088 and to Health Canada in Canada at 1-866-234-2345.