Decongestants are agents used to provide relief from the congestion that may occur when a person suffers from a cold, the flu, hay fever or sinusitis.

The inside of the nose is lined with small blood vessels. These vessels can become swollen if they are irritated in cases of infection or allergy, for example. The body’ immune response is to increase blood flow to these vessels. The swollen vessels can then obstruct the nasal airway, preventing nasal inhalation. In addition, affected areas in the nose become inflamed and the mucus glands secrete more mucus to trap pathogens, which can also block the nose and cause a sensation of “stuffiness.”
 

Nasal decongestants can relieve this blockage by reducing the swelling in the nasal airways, opening them up and allowing a person to breathe more easily. However, these agents can only provide short-term relief from congestion and do not cure the underlying cause of the condition.

These decongestants work by enhancing the action of adrenaline and noradrenalin through stimulation of the α-adrenergic receptors. This leads to constriction of the blood vessels in the nose, throat and paranasal sinuses. The drugs also inhibit the release of inflammatory mediators and reduce mucus formation in these areas.

The decongestants commonly contain either pseudoephedrine or phenylephrine and nasal sprays or eye drops often contain oxymetazoline. Pseudoephedrine has indirect effects on the adrenergic receptors, while phenylephrine and oxymetazoline activate the receptors directly.

Due to the widespread action of some decongestants, various side effects can occur such as high blood pressure due to blood vessel constriction, loss of sleep, anxiety, dizziness, nervousness, and excitability.

The body’s response to decongestants is quickly reduced with repeated use over a short time – an effect called tachyphylaxis – and the medications are not recommended for use in the long-term. In addition, using the agents for more than seven days can cause rebound congestion and block the nose even more once they are no longer used.

Decongestants are not to be used to treat children under twelve years of age, breastfeeding women or people with high blood pressure.