(ăn″tĭ-hĭs′tă-mēn)
[Pronunciation]
(-mĭn)

A drug that opposes the action of histamine.
Although there are two classes of histamine-blocking drugs, the term antihistamine is typically used to describe agents that block the action of histamines on H₁ receptors. These agents are used to treat allergies, hives, and other local and systemic hypersensitivity (allergic) reactions. Side effects of first-generation antihistamines (e.g, chlorpheniramine) include sedation, drying of mucous membranes, and urinary retention. Some first-generation antihistamines can also be used to treat insomnia, motion sickness, or vertigo. Second-generation agents (e.g., loratadine) tend to be less sedating, but still have beneficial effects in the treatment of allergies.

SYN: histamine blocking agent
See: histamine Poisons and Poisoning Appendix