Diphenhydramine (benadryl) has been on the market for a really long time, having been first approved in the 1940s. It’s also extremely cheap compared to many alternatives, but it’s extremely sedating and that’s just a characteristic nature of that compound
In contrast, some of the more modern antihistamines (Zyrtec, Allegra, Claritin, etc) were only approved for OTC use around the 2000s, with patent expiry on the name brands occuring around the end of that decade.
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