Beta blocker

A beta blocker is a drug that occupies beta-adrenergic receptors without switching them on, so the stress hormones epinephrine (adrenaline) and norepinephrine (noradrenaline) cannot act there; it is an antagonist of the fight-or-flight sympathetic nervous system. Beta-1 receptors sit mainly in the heart and in kidney cells that release renin, while beta-2 receptors sit mainly in the smooth muscle of the airways and blood vessels. Most have generic names ending in -olol, such as propranolol, atenolol and metoprolol.

Blocking beta-1 receptors slows the heart, weakens each contraction and cuts renin release, so the heart needs less oxygen and blood pressure falls. Beta blockers are therefore used for high blood pressure, angina, abnormal heart rhythms, after a heart attack and in long-term heart failure. They also help prevent migraine, ease tremor and the physical signs of anxiety, control symptoms of an overactive thyroid and, as eye drops, treat glaucoma. Cardioselective drugs act mostly on beta-1 receptors, while nonselective ones block beta-2 as well.

Common side effects are tiredness, cold hands and a slow pulse. Blocking beta-2 receptors can narrow the airways, so these drugs need care in asthma, and they can hide the warning signs of low blood sugar. James Black developed propranolol, the first beta blocker in wide use, in the 1960s and shared a Nobel Prize in 1988.