a powerful vasoconstrictor used to dilate the pupils and relieve nasal congestion

Phenylephrine is a chemical used as a drug that constricts blood vessels. It is given by injection to increase blood pressure, in a nasal spray to relieve nasal congestion, and in eye drops to dilate the pupils.

Phenylephrine or neosynephrine is an α-adrenergic receptor agonist used primarily as a decongestant, as an agent to dilate the pupil and, rarely, to increase blood pressure. As an oral decongestant, 6 out of 8 non-drug company sponsored FDA studies have shown phenylephrine to be no more effective than a placebo, as it is not effectively absorbed by the bloodstream prior to breakdown in the liver.