Their effectiveness by themselves in the common cold appears to have a small benefit in adults.
[1] Topical decongestants should only be used by patients for a maximum of 5–7 days in a row, because rebound congestion may occur in the form of rhinitis medicamentosa.
When used in adults for a short period of time side effects appear to be few.
[1] Topical decongestants are vasoconstrictors, and work by constricting the blood vessels within the nasal cavity.
This drug article relating to the respiratory system is a stub.