A decongestant (or nasal decongestant) is a type of pharmaceutical drug that is used to relieve nasal congestion in the upper respiratory tract. The active ingredient in most decongestants is either pseudoephedrine or phenylephrine (the latter of which has disputed efficacy).
These are alpha-agonists which on topical application as dilute solution (0.05-0.1%) produce local vasoconstriction. Regular use of these agents for long periods should be avoided because mucosal ciliary function is impaired: atrophic rhinitis and anosmia can occur due to persistent vasoconstriction.
Decongestants can be absorbed from the nose via an inhaler and produce systemic effects, mainly CNS stimulation and rise in blood pressure. These drugs should be used cautiously in hypertensives and in those receiving MAO inhibitors.
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.
Decongestant nasal sprays and eye drops often contain oxymetazoline and are used for topical decongestion. Pseudoephedrine acts indirectly on the adrenergic receptor system, whereas 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. Most decongestants, however, 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.
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: