Adrenergic blockers bind to the adrenergic receptors and prevent the action of adrenergic drugs. They may block alpha or beta receptors or both. Alpha 1 blockade results in a fall in blood pressure. Alpha 2 blockades enhance the release of noradrenaline resulting in hypertension. Effects of alpha blockade include—postural hypotension, palpitation, nasal stuffiness, miosis, impaired ejaculation and impotence. Prazosin is a potent, highly selective alpha 1 blocker with 1,000 time’s greater affinity for alpha 1 receptors. Alpha blockers are used in hypertension, pheochromocytoma, peripheral vascular diseases, congestive cardiac failure and benign prostatic hypertrophy. Beta blockers block the actions of catecholamine that are mediated through the beta receptors. Beta blockers decrease the heart rate, force of contraction and cardiac output; they also increase airway resistance—hence contraindicated in asthmatics. Cardio selective beta blockers like atenolol, metoprolol and esmolol selectively block beta 1 receptors and bronchospasm is negligible. Beta blockers are used in hypertension, angina pectoris, cardiac arrhythmias, myocardial infarction, congestive cardiac failure, obstructive cardiomyopathy, pheochromocytoma, thyrotoxicosis, glaucoma, prophylaxis of migraine and anxiety. Labetalol blocks both alpha 1 and beta 1 receptors.