Labetalol is a medication used to treat high blood pressure and in long term management of angina.

[4] Common side effects include low blood pressure with standing, dizziness, feeling tired, and nausea.

[4] Serious side effects may include low blood pressure, liver problems, heart failure, and bronchospasm.

[10] Labetalol is useful in the treatment of acute cardiovascular toxicity (e.g. in overdose) caused by sympathomimetics like amphetamine, methamphetamine, cocaine, ephedrine, and pseudoephedrine.

[16] Labetalol acts by blocking α- and β-adrenergic receptors, resulting in decreased peripheral vascular resistance without significant alteration of heart rate or cardiac output.

[19] The amount of α to β blockade depends on whether labetalol is administered orally or intravenously (IV).

[19][18] Labetalol's dual α- and β-adrenergic antagonism has different physiological effects in short- and long-term situations.

[23] During long-term use, labetalol can reduce heart rate during exercise while maintaining cardiac output by an increase in stroke volume.

[2] Similar to local anesthetics and sodium channel blocking antiarrhythmics, labetalol also has membrane stabilizing activity.

When labetalol is given in acute situations, it decreases the peripheral vascular resistance and systemic blood pressure while having little effect on the heart rate, cardiac output and stroke volume, despite its α1-, β1- and β2-adrenergic receptor blocking mechanism.

Thus, labetalol is able to reduce heart rate during exercise while maintaining cardiac output by the increase in stroke volume.

[31][3][32][33][34][2] In any case, labetalol, in animals including rats, rabbits, and dogs, was found to cross into the brain in negligible amounts, probably for reasons other than low lipophilicity.

[1] The minimum requirement for adrenergic agents is a primary or secondary amine separated from a substituted benzene ring by one or two carbons.

As the size of the substituent attached to the amine becomes greater, particularly with respect to a t-butyl group, then the molecule typically is found to have receptor affinity without intrinsic activity, and is, therefore, an antagonist.

[36] Labetalol, with its 1-methyl-3-phenylpropyl substituted amine, is greater in size relative to a t-butyl group and therefore acts predominantly as an antagonist.

[38] It is chemically designated in International Union of Pure and Applied Chemistry (IUPAC) nomenclature as 2-hydroxy-5-[1-hydroxy-2-[(1-methyl-3-phenylpropyl)amino]ethyl]benzamide monohydrochloride.