In 2020, it was the sixth most commonly prescribed medication in the United States, with more than 66 million prescriptions. Medical uses
Metoprolol is used for a number of conditions, including hypertension, angina, acute myocardial infarction, supraventricular tachycardia, ventricular tachycardia, congestive heart failure, and prevention of migraine headaches. It is an adjunct in the treatment of hyperthyroidism.The different salt versions of metoprolol – metoprolol tartrate and metoprolol succinate – are approved for different conditions and are not interchangeable.Off-label uses include supraventricular tachycardia and thyroid storm. Available forms
Metoprolol is sold in formulations that can be taken by mouth or given intravenously. The medication is often taken twice a day. The extended-release formulation is taken once a day. Metoprolol may be combined with hydrochlorothiazide (a diuretic) in a single tablet. Adverse effects
Adverse effects, especially with higher doses, include dizziness, drowsiness, fatigue, diarrhea, unusual dreams, trouble sleeping, depression, and vision problems. β-blockers, including metoprolol, reduce salivary flow via inhibition of the direct sympathetic innervation of the salivary glands. Metoprolol may also cause the hands and feet to feel cold.
Stopping this drug should be done slowly to decrease the risk of further health problems. Pregnancy and breastfeeding
Risk for the fetus has not been ruled out, per being rated pregnancy category C in the United States. Metoprolol is category C in Australia, meaning that it may be suspected of causing harmful effects on the human fetus (but no malformations). It appears to be safe in breastfeeding. Overdose
Excessive doses of metoprolol can cause severe hypotension, bradycardia, metabolic acidosis, seizures, and cardiorespiratory arrest. Blood or plasma concentrations may be measured to confirm a diagnosis of overdose or poisoning in hospitalized patients or to assist in a medicolegal death investigation. Plasma levels are usually less than 200 μg/L during therapeutic administration, but can range from 1–20 mg/L in overdose victims. Pharmacology
General pharmacological principles of metoprolol:
beta-1 selective
moderately lipophilic
without intrinsic sympathomimetic activity
with weak membrane stabilizing activity
decreases heart rate, contractility, and cardiac output, therefore decreasing blood pressure

Mechanism of action
Metoprolol blocks β1 adrenergic receptors in heart muscle cells, thereby decreasing the slope of phase 4 in the nodal action potential (reducing Na+ uptake) and prolonging repolarization of phase 3 (slowing down K+ release). It also suppresses the norepinephrine-induced increase in the sarcoplasmic reticulum (SR) Ca2+ leak and the spontaneous SR Ca2+ release, which are the major triggers for atrial fibrillation. Pharmacokinetics
It undergoes α-hydroxylation and O-demethylation as a substrate of the cytochrome liver enzymes CYP2D6. Chemistry
The active substance metoprolol is employed either as metoprolol succinate or as metoprolol tartrate (where 100 mg metoprolol tartrate corresponds to 95 mg metoprolol succinate).