Instructed patient in medication Metoprolol is used to treat high blood pressure. It also is used to prevent angina (chest pain) and to improve survival after a heart attack. If your doctor prescribes a low-salt or low-sodium diet, follow these directions carefully. Metoprolol may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away: dizziness or lightheartedness, tiredness, depression, nausea and dry mouth.