Phenylephrine [fen-ill-EF-rin] is a direct-acting, synthetic adrenergic drug that binds primarily to α receptors and favors α1 receptors over α2 receptors. It is not a catechol derivative and, therefore, not a substrate for COMT. Phenylephrine is a vasoconstrictor that raises both systolic and diastolic blood pressures. It has no effect on the heart itself but rather induces reflex bradycardia when given parenterally. It is often used topically on the nasal mucous membranes and in ophthalmic solutions for mydriasis. Phenylephrine acts as a nasal decongestant and produces prolonged vasoconstriction. The drug is used to raise blood pressure and to terminate episodes of supraventricular tachycardia (rapid heart action arising both from the atrioventricular junction and atria). Large doses can cause hypertensive headache and cardiac irregularities.