beta-blocker or beta-adrenergic blocking agent, drug that reduces the symptoms connected with hypertension, cardiac arrhythmias, angina pectoris, migraine headaches, and other disorders related to the sympathetic nervous system. Beta-blockers also are sometimes given after heart attacks to stabilize the heartbeat. Within the sympathetic nervous system, beta-adrenergic receptors are located mainly in the heart, lungs, kidneys, and blood vessels. Beta-blockers compete with the nerve-stimulating hormone epinephrine for these receptor sites and thus interfere with the action of epinephrine, lowering blood pressure and heart rate, stopping arrhythmias, and preventing migraine headaches. Because it is also epinephrine that prepares the body for "fight or flight" in stressful or fearful situations, beta-blockers are sometimes used as antianxiety drugs, especially for stage fright and the like. People taking a beta-blocker must avoid caffeine, alcohol, and salty foods, because the interaction of those substances and the drug can raise the heart rate and blood pressure. Propranolol (Inderal) is a commonly used beta-blocker.

in full beta-adrenergic blocking agent

Any of a class of synthetic drugs used to treat a wide range of diseases and conditions of the sympathetic nervous system (see autonomic nervous system). Stimulation by epinephrine of beta-adrenergic receptors, which are predominately found in the heart but are also present in vascular and other smooth muscle, results in excitation of the sympathetic nervous system. By preventing that excitation, beta-blockers are useful in controlling anxiety, hypertension, and a variety of heart conditions (see heart disease). They reduce the risk of a second heart attack.

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