Decongestants are medicines used to relieve nasal congestion (stuffy nose), a common symptom of colds and allergies. Congestion results when membranes lining the nose become swollen. Decongestants relieve this swelling by narrowing blood vessels that supply the nose. This reduces blood supply to the swollen membranes, causing them to shrink.

These medicines do not cure colds or reverse the effects of histamines—chemicals released as part of the allergic reaction. They relieve only the stuffiness. When considering whether to use a decongestant for cold symptoms, keep in mind that most colds go away with or without treatment and that taking medicine is not the only way to relieve a stuffy nose. Drinking hot tea or broth or eating chicken soup may help.

Decongestants are sold in many forms, including tablets, capsules, caplets, gelcaps, liqui-caps, liquids, nasal sprays, and nose drops. These drugs are sometimes combined with other...