Easy-to-read patient tips for metoprolol-tartrate covering how it works, benefits, risks, and best practices. Lopressor (metoprolol tartrate) Tablets and Injection is a selective beta-adrenoreceptor blocking agent (beta-blocker) used to treat high blood presure (hypertension), angina, and heart attacks. Overview: Metoprolol is a beta blocker. It is is used to treat high blood pressure, chest pain, heart failure, and lower the risk of a repeat heart attack. Common side effects include tiredness. Read on to learn about the side effects of metoprolol, including common, severe, and long-term side effects, and how to manage them. Metoprolol tartrate is used in people whose blood pressure and circulation are stable after a definite or suspected heart attack, to reduce the risk of dying from heart and blood vessel causes. In hospital, it may be started as an injection into a vein and then continued as tablets. The specific agent in on-market formulations of metoprolol is either metoprolol tartrate or metoprolol succinate, where tartrate is an immediate-release formulation and the succinate is an extended-release formulation (with 100 mg metoprolol tartrate corresponding to 95 mg metoprolol succinate). 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.