Used primarily in the management of pheochromocytoma, a tumor of the adrenal gland that causes excessive release of catecholamines. It helps control high blood pressure and other symptoms before surgery by blocking alpha-adrenergic receptors, preventing the action of adrenaline and noradrenaline. Also used off-label in certain cases of resistant hypertension and in the treatment of symptoms related to severe autonomic hyperreflexia. Due to its long-lasting effect, it provides sustained blockade even after plasma levels drop. Not typically used for routine hypertension because of its potent and irreversible action.