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Antihistamines are a class of substances that inhibit the action of histamine. Antihistamines are commonly used to relieve allergies and to promote sleep. Recreationally, very high doses can be used to induce delirium and achieve a hallucinogenic effect in which the user sees and hears fully-formed, extremely convincing hallucinations. However, this experience is typically considered highly unpleasant by most users.
The toxicity of recreational antihistamine use is poorly understood, although there is some evidence that abuse may cause cognitive deficits and other health issues.
Most antihistamines act as inverse agonists on histamine receptors, meaning they inhibit the action of histamine by preventing it from binding to them. They may also inhibit the enzymatic activity of histidine decarboxylase which catalyzes the transformation of histidine into histamine.
Antihistamines are found throughout organic chemistry and include psychoactive and anti-allergenic compounds.
- Emanuel, M. B. (1999). Histamine and the antiallergic antihistamines: a history of their discoveries. Clinical & Experimental Allergy, 29(S3), 1-11. https://doi.org/10.1046/j.1365-2222.1999.00004.x-i1
- Sicherer, Scott H. M.D., Understanding and Managing Your Child's Food Allergy. Baltimore: The Johns Hopkins University Press, 2006 ISBN 0-8018-8492-6.