<p>Labetalol is a competitive antagonist at b1&nbsp;and b2&nbsp;adrenoreceptors and has some intrinsic activity at b2&nbsp;adrenoreceptors. Labetalol has, in addition to its b-blocking action, a competitive antagonist action at postsynaptic a-adrenoreceptors. In isolated tissues Labetalol is four to eight times more potent at b than a-adrenoreceptors.</p>