Metoprolol is a drug that belongs to the group of selective β1 receptor blockers. It acts due to its influence on the heart and blood flow. Metoprolol can be used for the treatment of such conditions as hypertension, coronary artery disease, angina pectoris, acute myocardial infarction (treatment and secondary prophylaxis), cardialgia, vasovagal syncope, supraventricular tachycardia, ventricular tachycardia, long QT syndrome, congestive heart failure, hypertrophic cardiomyopathy, thyrotoxicosis (as a part of complex therapy) and prevention of migraine headaches.
According to studies, about 27% of patients who use Metoprolol experience at least one side effect. Some of them are mild and transient but can be quite serious and require urgent medical attention. Metoprolol can be metabolized in two ways and patients who are slow metabolizers may experience severe side effects more often.
Most common side effects of Metoprolol:
- Tinnitus (ringing in one or both ears)
- Foggy thinking
- Fainting spells
- Short-term memory loss
- Cold, tingling, or numbness in fingers and toes
- Muscle pain
- Mild flu symptoms (chills, fever, runny nose, cough and sore throat)
- Increased asthma attacks in patients with pre-existing asthma
- Shortness of breath
- Low blood pressure
- Chest pain
- Slow heart rate
- Difficulty in swallowing
- Increased thirst
- Dry mouth
- Stomach pain
- Decreased urination
- Reversible hair loss (alopecia)
- Dry mouth or eyes
- Eye pain
- Decreased vision clearness
- Yellowing of the skin or eyes
- Swelling and redness at injection site
- Unexplained rash
- Sexual dysfunction
- Erectile dysfunction
- Peyronie’s disease
Other less common side effects of Metoprolol:
- Worsening of psoriasis
- Diabetes mellitus
- Red, swollen, blistered, or peeling skin
- Generalized psoriasiform lesions
- Arterial insufficiency of the Raynaud type
- Emotional lability
- Slightly clouded sensorium
- Retroperitoneal fibrosis
Sudden discontinuation of the use of Metoprolol can also cause side effects. It can cause such adverse reactions as sweating, chest pain, breathing difficulty and arrhythmia (irregular or fast heartbeat). In patients suffering from angina pectoris, discontinuation of Metoprolol intake can cause very serious aggravation of the angina symptoms.
Like any other medicine, Metoprolol can cause allergic reactions that can manifest as
- Severe dizziness
- Unexplained rash
- Unexplained swelling of the face, eyes, mouth, lips, tongue, neck
- Unusual hoarseness
- Difficulty in breathing or swallowing
- Tightness in the chest
Serious side effects
Patients who use Metoprolol can experience serious adverse effects that may require emergency medical help. Such side effects include:
- Unexplained swelling the arms, legs, hands, or feet (peripheral edema)
- Sudden weight gain
- Arrhythmia (severe bradycardia or irregular heartbeat)
- Heart block of the first-, second- or third-degree
- Intensification of AV block
- Variant angina pectoris (coronary artery spasm)
- Congestive heart failure
- Cardiogenic shock (especially when used post myocardial infarction)
- Increased bronchospasm
- Severe respiratory distress
- Severe dizziness or lightheadedness
- Bowel or urethral obstruction
- Hyponatriemia (confusion, seizures, sluggishness)
- Unusual bruising or bleeding
- Disorientation for time and place
- Mental depression up to catatonia
- Polymyalgia rheumatica
Metoprolol can cause aggravation of breathing difficulties in patients with obstructive lung diseases such as asthma, chronic bronchitis, or emphysema.
Changes in laboratory tests
Metoprolol also can cause some changes in your blood tests. So if your blood tests reveal such biochemical abnormalities as increased liver enzymes (alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase and lactic dehydrogenase), dyslipidemia (elevated serum triglyceride, very low density lipoproteins (VLDL) and significantly decreased high density lipoproteins (HDL)) you should keep in mind that these can be as a result of the adverse effects of Metoprolol.
Metoprolol can also cause low blood sugar levels (hypoglycemia), increased serum potassium levels (hyperkalemia), and low blood sodium levels.
Hematological picture during Metoprolol’s intake can be changed in such way as agranulocytosis, microcytic anemia, non-thrombocytopenic purpura, thrombocytopenic purpura.
Hormonal tests can show decreased free and total testosterone and slightly decreased T3 concentrations in serum.
Side effects in pregnant women
There were no proper studies yet to establish the safety of Metoprolol during pregnancy. However, some data show that Metoprolol can slow fetal growth.
Nursing mothers should use this medicine under a doctor’s supervision because Metoprolol may pass into breast milk and cause side effects in the infant.
Side effects in children
There were no proper studies yet to establish the safety of Metoprolol in children.
You may never experience any of the side effects listed above. Your doctor cannot predict your body’s reaction to Metoprolol until you have tried it. That is why you should immediately inform your doctor of any changes in your health condition after taking Metoprolol. Therefore, when you feel something is wrong, ask your doctor for advice and he or she will diagnose if your problem is connected with the medicine intake. You should also be careful because some of the side effects of Metoprolol require urgent medical attention. In addition, it is strongly recommended not to stop Metoprolol intake suddenly because this can lead to worsening of your symptoms.