by ButterflyEffect

Now we turn to phenylephrine. As you can see, that's a somewhat different structure - there's a phenol on the aryl ring, and there's no longer a chiral methyl group bretween the hydroxy and the N-methyl. It also has adrenergic effects, but different (and often weaker) ones than either ephedrine or pseudoephedrine. Its main effect seems to be raising blood pressure, and it has medical uses in that area as an addition to anaesthesia agents. But what it does not do well is act as a decongestant. There have been several controlled studies that show that it is indistinguishable from placebo in conditions like allergic rhinitis. Pseudoephedrine, however, is very clearly distinguished from placebo and in most people has very noticeable decongestant effects that last for several hours.