A medication that blocks the action of histamine, a chemical released during allergic reactions. Used to treat symptoms like sneezing, itching, runny nose, and hives.
From Greek 'anti' meaning against and 'histamine' from Greek 'histos' (tissue) and 'amine' (containing nitrogen). Histamine was discovered in 1910, and antihistamines were developed in the 1940s when scientists learned how to block its effects.
Antihistamines don't just treat allergies - many cause drowsiness because histamine is also a neurotransmitter that keeps you awake! That's why Benadryl makes you sleepy, and why newer 'non-drowsy' antihistamines were specifically designed not to cross into the brain where they'd affect your sleep-wake cycle.
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