Related Terms

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Brand Names

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Background

• Antihistamines, also called H1 blockers, are medicines that help alleviate allergy symptoms such as itchy eyes, sneezing, runny nose, and occasional itchy rashes (especially hives).
• An allergy or hypersensitivity reaction occurs when the body's immune system overreacts to a substance that is normally harmless (allergen), such as mold, pollen, animal dander, or dust mites. The white blood cells of an allergic individual produce an antibody called immunoglobulin E (IgE), which attaches to the allergen. This triggers the release of histamine and other chemicals that cause allergic symptoms, such as runny nose, watery eyes, and hives. Histamine may also cause the airway passages to close making it difficult to breathe.
• Antihistamines block histamine-1 receptors in the gastrointestinal tract, respiratory tract and blood vessels of an allergic individual. This prevents the release of histamine in response to an allergen. As a result, allergy symptoms are minimized.
• Antihistamines are available as short-lasting or long-lasting medications. The type of medication used depends on how frequent allergy symptoms arise. Some antihistamines are available over-the-counter, while others, especially long-lasting antihistamines, are only available by prescription. The most common side effect associated with antihistamines is drowsiness. However, prescription antihistamines generally do not cause drowsiness.
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Short-Acting Antihistamines

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Long-Acting Antihistamines

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Additional Uses

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Side Effects

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Pregnancy and Breastfeeding

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Children

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Older Adults

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Possible Interactions

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Integrative Therapies

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Author Information

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References

Natural Standard developed the above evidence-based information based on a thorough systematic review of the available scientific articles. For comprehensive information about alternative and complementary therapies on the professional level, go to www.naturalstandard.com. Selected references are listed below.

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