Metoprolol succinate (Toprol-XL) belongs to a group of drugs called beta-blockers. Doctors commonly prescribe this drug to treat high blood pressure, heart failure and heart-related chest pain called angina. Metoprolol succinate ER is a long-acting, once daily form of metoprolol. The "ER" stands for extended release. A wide variety of side effects are possible with metoprolol succinate, ranging from nausea and fatigue to potentially serious heart rhythm abnormalities and shortness of breath. The 50-mg dose of metoprolol succinate ER is a mid-range amount. Side effects might be more common with higher doses.
The most common side effects of metoprolol succinate relate to its actions as a beta-blocker. It prevents the hormone adrenaline from binding to matching receptors in the brain, heart, blood vessels and kidneys. These actions reduce the body's flight-or-fight response and can produce certain nervous system side effects. The most common is fatigue, which occurs in at least 10 percent of people, according to the manufacturer's prescribing information. Headache and dizziness reportedly occur in 1 to 9.9 percent of the people and dizziness in less than 2 percent. More rare nervous system side effects include short-term memory loss, nightmares, anxiety, hallucinations and confusion.
Toprol XL product information published by the manufacturer describes several digestive system side effects that can occur in people taking metoprolol succinate. According to the manufacturer, the most common digestive problems that occur in 1 to 9.9 percent of people taking the medication include nausea, diarrhea, constipation and abdominal pain. Less common possible side effects include vomiting, heartburn, dry mouth and stomach gas. Rarely, metoprolol has been linked to liver inflammation.
Although metoprolol succinate can benefit people with heart disease, it can also cause unwanted side effects involving the heart and circulatory system. July 2014 information from the manufacturer's prescribing information indicates the most negative effect is a slow heart rate, occurring in 1.5 percent of people taking the medication. Other possible side effects include low blood pressure, irregularities in the heart rhythm, chest pain, cold hands and feet, and worsening heart failure symptoms -- such as lower extremity swelling, severe fatigue and shortness of breath.
Beta-blockers such as metoprolol succinate can also cause side effects in the lungs. Less than 10 percent of people might experience shortness of breath during physical exertion, according to the manufacturer. A sudden tightening of the lung airways called bronchospasm is much less common, occurring is less than 1 percent of people on metoprolol. People with asthma and chronic obstructive pulmonary disease, or COPD, are more likely than others to experience this side effect. Although uncommon, metoprolol-related bronchospasm can lead to severe difficulty breathing and the need for emergency care. Symptoms of bronchospasm include chest tightness, severe shortness of breath and dizziness.
Rare but Significant Side Effects
Rare heart-related side effects of metoprolol include severe heart rhythm disturbances, which often occur due to the drug's interference with the electrical signaling system of the heart that stimulates the regular beating of the heart. Other possible rare side effects of metoprolol include:
-- Problems with sexual performance of loss of interest in sex.
-- Taste disturbance.
-- Increased sweating.
-- Blurred vision.
-- Hair loss.
-- Severe allergic reactions.
The U.S. Food and Drug Administration has classified metoprolol succinate as a pregnancy category C drug. This classification indicates that animal studies have shown there is a possible risk to the unborn baby, but there are no human studies. With a pregnancy category C drug, the decision to prescribe the medication is made on a case-by-case basis, weighing the potential benefits for the mother vs. the potential risks for the unborn baby. Because a small amount of metoprolol passes into breast milk, new mothers should talk with their doctor about whether breastfeeding is advisable.
Warnings and Precautions
You should not stop taking metoprolol or alter the dose without your doctor's approval. Severe changes in heart rate can occur that may result in death if metoprolol succinate is stopped abruptly or discontinued without tapering the dose. The FDA recommends that the drug be tapered off over a 1- to 2-week period with close monitoring by a healthcare practitioner.
Seek emergency medical care if you experience chest pain, swelling of the face or throat, shortness of breath or sudden fatigue while taking metoprolol or after a change in dosage.