Beta blocker: A class of drugs that block beta-adrenergic substances such as adrenaline (epinephrine) in the "sympathetic" portion of the autonomic (involuntary) nervous system. By blocking the action of the sympathetic nervous system on the heart, beta blockers relieve stress on the heart; they slow the heart beat, lessen the force with which the heart muscle contracts, and reduce blood vessel contraction in the heart, brain, and throughout the body. Beta blockers may be used to treat abnormal heart rhythms (cardiac arrhythmias) and prevent abnormally fast heart rates (tachycardias) or irregular heart rhythms such as premature ventricular beats. Since beta blockers reduce the demand of the heart muscle for oxygen and the chest pain of angina pectoris occurs when the oxygen demand of the heart exceeds the supply, beta blockers can be useful in treating angina. They have also become an important drug in improving survival after a person has had a heart attack. Thanks to their effect on blood vessels, beta blockers can lower the blood pressure and be of value in the treatment of hypertension. Other uses for beta blockers include the prevention of migraine headaches and the treatment of certain types of tremors (familial or hereditary essential tremors).

The beta blockers (with brand names) include:

• acebutolol (Sectral),
• atenolol (Tenormin),
• bisoprolol (Zebeta),
• metoprol (Lopressor, Lopressor LA, Toprol XL),
• nadolol (Corgard), and
• timolol (Blocadren).

Beta blockers are also available in combination with a diuretic as, for example, with bisoprolol and hydrochlorothiazide (Ziac).

Beta blockers reduce the pressure within the eye (the intraocular pressure), probably by reducing the production of the liquid (aqueous humor) within the eye, and so are used to lessen the risk of damage to the optic nerve and loss of vision in glaucoma. Beta blocker preparations for this purpose include timolol ophthalmic solution (Timoptic) and betaxolol hydrochloride (Betopic, Betopic S).