The ingredient of Betalock is metoprolol, and the antihypertensive effect of metoprolol enalapril will be increased by the combined use of metoprolol. Metoprolol is a β-blocker, through the inhibition of β-receptors to weaken myocardial contractility, inhibition of sympathetic tone and renin secretion and blood pressure decline. Enalapril is an angiotensin-converting enzyme inhibitor, which reduces the action of angiotensin and dilates blood vessels to lower blood pressure. The mechanism of action of metoprolol and enalapril is different, and the combined use of the two drugs can increase the effect of lowering blood pressure, which is suitable for patients with hypertension accompanied by coronary heart disease and fast heart rate. The adverse reactions of metoprolol include cold limbs, bradycardia, dizziness, hypotension, dyspnea, etc. It is forbidden for patients who are allergic to the drug components, bronchial asthma, severe bradycardia and cardiogenic shock. Adverse reactions of enalapril include hypotension, dizziness, dry cough, stomach upset, elevated blood potassium, etc. It is contraindicated in patients with hypersensitivity to drug components, bilateral renal artery stenosis, and severe renal impairment. When metoprolol and enalapril are combined to lower blood pressure, the drug should be used under the guidance of a physician and the appropriate dose should be selected.