Toprol-XL^® (metoprolol succinate) is a prescription medication that belongs to a class of drugs known as beta blockers. The medication is licensed to treat high blood pressure (hypertension), congestive heart failure, and symptoms of angina. Toprol-XL works by reversing the effect of certain stress hormones. This reaction can decrease heart rate, blood pressure levels, and the workload of the heart. Examples of side effects that may occur with Toprol-XL include dizziness, slow heart rate, and itching. Toprol-XL is available in four different strengths.