decongestant

A decongestant clears a stuffy nose by shrinking the swollen blood vessels in the lining. A blocked nose comes mostly from engorged vessels and swollen tissue; a decongestant tightens those vessels so the passages open and air flows again.

Decongestants are sympathomimetics that activate alpha-adrenoceptors on nasal blood vessels, causing them to constrict and reducing mucosal swelling. They come as sprays or drops (oxymetazoline, xylometazoline) that act locally and quickly, and as oral tablets (pseudoephedrine, phenylephrine) that act more broadly. By narrowing vessels they reduce the congestion of colds and allergic rhinitis.

Topical sprays carry a well-known trap: used for more than a few days they can cause rebound congestion (rhinitis medicamentosa), so the stuffiness returns worse when stopped — hence the short-course rule. Oral decongestants can raise blood pressure and heart rate and cause restlessness or insomnia, making them risky in hypertension, heart disease and certain other conditions, and pseudoephedrine is restricted in many places because it can be misused to make illicit drugs.