Read on to learn about the side effects of metoprolol, including common, severe, and long-term side effects, and how to manage them. Metoprolol, sold under the brand names Lopressor and Toprol-XL among others, is a medication used to treat angina, high blood pressure and a number of conditions involving an abnormally fast heart rate. [5] Metoprolol is a beta-blocker that affects the heart and circulation (blood flow through arteries and veins). Metoprolol is used to treat angina (chest pain) and hypertension (high blood pressure). Metoprolol is also used to lower your risk of death or needing to be hospitalized for heart failure. Find patient medical information for Metoprolol (Lopressor, Toprol XL, others) on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user ratings Metoprolol is in a class of medications called beta blockers. It works by relaxing blood vessels and slowing heart rate to improve blood flow and decrease blood pressure. Metoprolol (Lopressor®) is a medication that lowers your blood pressure and heart rate, making it easier for your heart to pump blood to the rest of your body. Metoprolol is used alone or together with other medicines to treat high blood pressure (hypertension). High blood pressure adds to the workload of the heart and arteries. If it continues for a long time, the heart and arteries may not function properly.