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Comment by linsomniac | Hacker News Reader

That seems to be only for first generation, drowsy-making, tablets. Second gen formulas don't cross over the blood/brain barrier.

https://www.myalzteam.com/resources/zyrtec-and-alzheimers-me...

There IS one year-old finding that suddenly stopping Zyrtec after daily 3-month use may lead to nasty itching, and if that happens you can re-start and then taper off. https://www.fda.gov/drugs/drug-safety-communications/fda-req...

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Zyrtec/cetirizine is a weird one. Everyone seems to agree that it is a second-generation antihistamine. The FDA seems to play along. But there is no particular shortage of anecdotal evidence of people who find it quite sedating (hi there!), there are some papers questioning its status [0], and the FAA puts it in a category with diphenhydramine, not with loratadine and fexofenadine [1].

[0] https://pmc.ncbi.nlm.nih.gov/articles/PMC1118461/

[1] https://www.faa.gov/ame_guide/media/AllergyAntihistamineImmu...

Ceterizine does cross the BBB to some extent, just less so than a lot of furst gen ones. So it can still have some hypnotic effects, sure.

But that's not the important difference here. The important difference is that ceterizine has negligible antimuscarinic effects, unlike DPH, meclizine, cyclizine et al. Antimuscarinics are nasty drugs, and the antimuscarinic activity(and sometimes other non-histaminergic activity as well) is why a lot of first generation antihistamines are so bad for your brain.

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