Decongestants are a type of medication capable of relieving many of the symptoms associated with common colds, the flu and allergies (e.g., sneezing, coughing, runny nose). They work by reducing congestion of the nose and sinuses. The two main types of decongestants used to treat these conditions are pseudoephedrine and phenylephrine.

Decongestants treat the symptoms associated with allergic rhinitis (hay fever), non-allergic rhinitis (colds and the flu), sinusitis and allergic conjunctivitis (eye allergies). They do not treat the underlying cause of the symptoms.

Decongestants work by affecting small blood vessels in the nose. These blood vessels often fill with blood and swell during bouts with a cold or the flu. This narrows the nasal passages and makes it difficult for a person to breathe. Decongestants cause constriction of the blood vessels, which forces blood out of the vessels and opens up the breathing passageways. Decongestants also allow the tissue in the inner eyelid to shrink, which reduces eye irritation.

Although decongestants are available in over-the-counter formulations, some no longer appear on store shelves. In January 2006, federal legislation took effect that mandated that all drug products containing the drug pseudoephedrine be kept behind the pharmacy counter. Pseudoephedrine is a major ingredient in making methamphetamine, a highly addictive illegal substance. The goal of this legislation is to make it more difficult for people to obtain pseudoephedrine to make methamphetamine.

In addition, in 2000, the U.S. Food and Drug Administration (FDA) determined that the ingredient phenylpropanolamine, which has been used as a decongestant in various prescription and over-the-counter cough medications, is not safe for use. Research indicated that its use is associated with an increased risk of hemorrhagic stroke (bleeding in the brain). 

To purchase decongestants with pseudoephedrine, a person needs to speak to a pharmacist, show a form of identification and sign a logbook. People are limited to purchasing 3.6 grams in a single day and 9 grams per month at a retail store.