Daily allergy tablets are associated with huge increases in early onset Alzheimer’s. Glad you found something that works, but might be good to get some of the allergen injections :)
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...
[0] https://pmc.ncbi.nlm.nih.gov/articles/PMC1118461/
[1] https://www.faa.gov/ame_guide/media/AllergyAntihistamineImmu...
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.
All I can find is about 1st gen antihistamines (i.e. Benadryl, which I doubt many people take daily, because of the drowsiness).
Even for those, evidence seems to be mixed at best. "Huge increases" seems like hyperbole.
Only first-generation antihistamines with anticholinergic effects are associated with cognitive decline in elderly patients.
Yet here we are, warning each other about the dangers of LLM hallucinations. Humans "hallucinate" (provide random authoritative-looking information without anything to back it up) pretty often too.
I think this post is a decent summary, the answer is a soft maybe: https://www.health.harvard.edu/mind-and-mood/should-i-worry-...
Second-gen tablets might increase dementia risk by a small-to-medium amount (there's almost certainly still a small degree of CNS activity, and we don't know what causes dementia in the first place), but researching it will be difficult. Dementia is hard to research because of how long it takes to develop, and it's poor coding within health data, and antihistamines are hard to research because they're not often prescribed and aren't available in the health data.
If it's a large effect, those factors wouldn't matter, but smaller risks are harder to detect and more sensitive to bias. If you want to minimise dementia risk, then reducing antihistamine use might be warranted, but you're probably better off addressing the risk factors we do know about: https://www.dementia.org.au/brain-health/risk-factors-develo...
You didn't read it very closely, I posted it specifically BECAUSE it cites sources (14 of them by my count).
edit: I sit corrected, if I open it in Incognito mode the citations are removed. That's not very useful.
edit 2: Here is a gist with the citations: https://gist.github.com/linsomniac/6d2bdeb0f63cf504354b067e2...