A member asked:

Can you tell me how anti-histamines make people drowsy ?

9 doctors weighed in across 2 answers
Dr. Alan Ali answered

Specializes in Psychiatry

Anti-histamines: They can be h1-receptor antagonists such as Benadryl (diphenhydramine) or periactin or loratadine. Or, h2-receptor antagonists such as tagamet or ranitidine. Or, h3/h4 receptor antagonists (experimental) such as thioperamide. Or, atypical antihistamines such as catechin. Or, others such as cromolyn.

Answered 4/2/2015

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Dr. John Chiu answered

Specializes in Allergy and Immunology

Yes: Histamine's action on the brain's histamine receptors keeps you alert. When the antihistamine enters the brain , it counteracts this stimulatory effect thereby making you drowsy. Since the 2nd generation antihistamines do not enter the brain , they are not expected to cause drowsiness.

Answered 5/17/2015

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