A decongestant or nasal decongestant is a type of drug which is used to relieve nasal congestion.

The vast majority of decongestants act via enhancing norepinephrine (noradrenaline) and epinephrine (adrenaline) or adrenergic activity by stimulating the α-adrenergic receptors. This induces vasoconstriction of the blood vessels in the nose, throat, and paranasal sinuses, which results in reduced inflammation (swelling) and mucus formation in these areas.

The active ingredients in most ingested decongestants are pseudoephedrine or phenylephrine. Decongestant nasal sprays and eye drops often contain oxymetazoline and are used for topical decongestion. Pseudoephedrine acts indirectly on the adrenergic receptor system while phenylephrine and oxymetazoline are direct agonists. The effects are not limited to the nose and these medicines may cause hypertension (high blood pressure) through vasoconstriction, but most decongestants are not pronounced stimulants due to lack of response from the other adrenoreceptors. Besides hypertension, common side effects include sleeplessness, anxiety, dizziness, excitability, and nervousness.

Decongestants are normally paired with antihistamines to lessen this effect, but the combination of both classes of drugs do not necessarily cancel the side effects of each other.

Topical nasal or ophthalmic decongestants quickly develop tachyphylaxis (a rapid decrease in the response to a drug after repeated doses over a short period of time). Long-term use is not recommended since these agents lose effectiveness after a few days.

Common decongestants include:

• Ephedrine
• Levo-methamphetamine
• Naphazoline
• Oxymetazoline
• Phenylephrine
• Phenylpropanolamine
• Propylhexedrine
• Pseudoephedrine
• Synephrine
• Tetrahydrozoline

Uncommon and/or discontinued decongestants include:

• Cyclopentamine
• Epinephrine
• Fenoxazoline
• Levonordefrin
• Mephentermine
• Metizoline
• Norepinephrine
• Tramazoline
• Tuaminoheptane
• Tymazoline