Phenylephrine, one of the most common nasal decongestants, is included in a variety of topical preparations to relieve the symptoms of hay fever and head colds. It is also included in some tablets for the relief of cold and flu symptoms.
In small doses, the drug can reduce the pain of conjunctivitis by constricting blood vessels in the lining of the eye. It is also used to dilate the pupil during eye examinations and eye surgery.
Care should be taken not to exceed the recommended dose because this may produce congestion and swelling in the nasal passages or cause increased eye irritation (eye drops). High or prolonged doses of phenylephrine are liable to cause a rebound of nasal stuffiness and a rise in blood pressure and heart rate, and should therefore be avoided by people who have heart trouble or high blood pressure.