Phenylephrine is a selective α1-adrenergic receptor

Alpha-1 adrenergic receptor

The alpha-1 adrenergic receptor is a G protein-coupled receptor associated with the Gq heterotrimeric G-protein. It consists of three highly homologous subtypes, including α1A-, α1B-, and α1D-adrenergic...

 agonist

Agonist

An agonist is a chemical that binds to a receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance...

 used primarily as a decongestant

Decongestant

A decongestant or nasal decongestant is a type of drug that is used to relieve nasal congestion.-Pharmacology:The vast majority of decongestants act via enhancing norepinephrine and epinephrine or adrenergic activity by stimulating the α-adrenergic receptors...

, as an agent to dilate the pupil

Pupil

The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...

, and to increase blood pressure

Blood pressure

Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

. Phenylephrine has recently been marketed as a substitute for pseudoephedrine

Pseudoephedrine

Pseudoephedrine is a sympathomimetic drug of the phenethylamine and amphetamine chemical classes. It is used as a nasal/sinus decongestant and stimulant, or as a wakefulness-promoting agent....

 (e.g.,Sudafed

Sudafed

Sudafed is a brand name and registered trademark for over the counter decongestants manufactured by McNeil Laboratories for sale in Australia, New Zealand, Canada, Ireland, the United Kingdom, and the United States...

 (Original Formulation)), but there are claims that oral phenylephrine may be no more effective as a decongestant than a placebo

Placebo

A placebo is a simulated or otherwise medically ineffectual treatment for a disease or other medical condition intended to deceive the recipient...

 (see questions about effectiveness below).
Phenylephrine is used as a decongestant sold as an oral medicine, as a nasal spray

Nasal spray

Nasal sprays come in a variety of forms. Medicated such as Astelin, Afrin and Nasonex and natural such as Sinusoothe and Sterimar. Although delivery methods vary, most nasal sprays function by instilling a fine mist into the nostril by action of a hand-operated pump mechanism.-Antihistamine nasal...

, or as eye drops.