Antihistamines: Overview

Antihistamines are drugs that are used to treat a number of allergic health conditions by blocking the effects of a protein called histamine.

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Antihistamines are available in tablet or capsule (oral) form, as creams, lotions and gels (topical form), and as a nasal spray.


Antihistamines work by preventing the actions of histamine, which is a protein produced by the body as part of its natural defences.  Although histamine is generally useful, it is sometimes necessary to use antihistamines to block its effects.  For example, when there is an excessive allergic reaction to harmless substances such as pollen.


Serious drowsiness can be caused by so-called 'first-generation' antihistamines such as diphenhydramine and chlorphenamine.  People who regularly take first-generation antihistamines are more likely to be involved in serious accidents.  Second-generation antihistamines in general do not cause drowsiness; examples of these include loratadine and cetirizine.

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Antihistamines can help with the following:


Allergic Rhinitis / Hay Fever

Antihistamines, commonly available as sprays or tablets, stop the release of the chemical histamine released by the immune system.  They usually effectively relieve symptoms of runny nose, itching, and sneezing.

Eyes / Ocular

Allergic Conjunctivitis

Antihistamine drops are placed directly into the eye.


Meniere's Disease

While originally developed to treat allergy symptoms, most Meniere's disease patients are now prescribed antihistamines to treat vertigo.  Antihistamines are believed to suppress vertigo symptoms by blocking certain chemical pathways in the brain.  However, not all antihistamines are effective in suppressing vertigo: Antihistamines that do not have a sedative effect do not cross the blood-brain barrier and, therefore, cannot penetrate the inner ear or balance centers enough to be helpful.



Antihistamines can relieve itching and break the 'itch-scratch-itch' cycle which many eczema sufferers say is the worst symptom.  Although scratching relieves an itch, it also worsens inflammation and itching by causing more inflammatory substances to be released in the skin.

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