Benadryl is a brand name allergy medicine manufactured by Johnson & Johnson subsidiary McNeil Healthcare (UK) Limited (prior to 2006, it was a Pfizer product). Benadryl is used as an antihistamine for the temporary relief of seasonal and perennial allergy symptoms. It will also help with normal symptoms of insect stings even if there is no allergic reaction. Benadryl is available for oral or topical use.
In the United States and Canada, Benadryl products contain the 1st generation antihistamine Diphenhydramine. Diphenhydramine is used as an allergy treatment in various forms around the world. Diphenhydramine is an H-1 receptor antagonist. Antagonism is achieved through blocking the effect of histamine more than blocking its production or release. Diphenhydramine inhibits most responses of smooth muscle to histamine and acts as a vasoconstrictor by inhibiting the vasodilator effects of histamine. The antagonism may also produce anticholinergic effects, antiemetic effects, and significant sedative side effects.
In the United Kingdom, Benadryl products contain either the 2nd generation antihistamine acrivastine (sold as Benadryl Allergy Relief, with a suggested efficacy duration of eight hours) or the antihistamine cetirizine (sold as Benadryl Once a Day). Cetirizine is indicated for the relief of symptoms associated with allergy and hives. Cetirizine is an orally active and selective H1-receptor antagonist.