Decongestants are used to relieve congestions (constricting the blood vessel) developed during an allergic reaction (for example nasal Decongestantsblockage), often prescribed along with antihistamines. They can be used in various forms such as systemic as pills ( Pseudoephedrine –Sudafed tablets or liquids -for nasal decongestion),  local as sprays, drops and liquid; nasal decongestant as (xylometazoline, oxymetazoline) ocular decongestants( nephazoline, oxymetazoline, tetrahydrozoline for removal redness from eye) etc. Combinations of decongestants and antihistamines: such as Allegra-D or Zyrtec-D. 

Long term uses in particular local decongestants has potential side effects therefore, only for a few days at a time should be used. For instances, using of nasal sprays more than 7 days may damage the tissues of the nose and cause worsening of symptoms, a condition called ‘rhinitis medicamentosa’. However, systemic decongestants may be taken longer.