Black box warnings are the strictest warnings issued by the U.S. Food and Drug Administration (FDA). Black box warnings are issued when there is significant evidence that a drug or product is associated with an adverse reaction that may lead to death or serious injury. Metoprolol, like other beta-blockers, comes with a black box warning that abrupt cessation of therapy can cause a worsening of angina and, in some cases, a heart attack. The warning states that patients with heart disease are at the biggest risk, but that people taking it only for high blood pressure (hypertension) should also avoid abruptly stopping treatment. According to the warning, patients stopping therapy should slowly reduce the amount they take over a 1-2-week period, based on the advice and under the close supervision of a physician. You should always take metoprolol exactly as instructed by your doctor.