Purity >98%. L-Phenylephrine is an adrenergic Alpha1A receptor agonist (Ki = 1.4 μM) that demonstrates selectivity against the Alpha1B and Alpha1C receptor subtypes (Ki s = 23.9 and 47.8 μM, respectively). By stimulating adrenergic Alpha1 receptors, L-phenylephrine can induce aortic smooth muscle contractions, although reported relative affinity and potency values in rabbit are 5-fold weaker compared to that of L-norepinephrine. This compound is frequently used to precontract smooth muscle in preparations designed to study the properties of various vasodilator agents. Because L-phenylephrine acts on adrenergic Alpha1 receptors in the arterioles of the nasal mucosa to produce constriction, it has been examined clinically as an oral decongestant.