As far as i know anti-histamines do not have Serotonin reuptake inhibition, the only exception to that would be Diphenhydramine but apparently it's really weak reuptake inhibition if there's even any at all at the usual dosages.
Personally i've never had nor noticed any issues at all taking anti-histamines with Aya, i take heavy Harmala dosages daily and have for years, i've never avoided anti-histamines if i needed them, i've taken Cetirizine, Diphenhydramine, Loratadine, and i think a couple others. The only thing about Diphenhydramine and Loratadine is that they are metabolized by CYP2D6 (and to some extent by CYP1A2 as well for Diphenhydramine), which CYP2D6 (as well as CYP1A2) is potently inhibited by Harmalas, which can simply require cutting the dosage of the 2D6 (or 1A2) substrate in half, possibly down to a quarter, which i do with my night med Tizanidine as well (which is metabolized by CYP1A2) and as such i only require 2 to 4mgs of Tizanidine for the same effect i'd get from 8 to 10mgs by potentiating it with the 1A2 inhibition.
The only side-effect/adverse effect i've noticed with any of the anti-histamines i've tried would be the time Diphenhydramine gave me Exploding Head Syndrome twice in one night only to never happen again, but that was likely because i was taking 50mgs of Diphenhydramine at bed time around 6 to 8 hours into the Harmalas when the CYP2D6/1A2 inhibition was most potent and thus i was likely taking more along the lines of like 100 to 150mgs of Diphenhydramine, and plus it has a long duration which can even be stretched out by CYP inhibition and so it likely caught up to me as the nights followed and i continued taking it, which i took it for a week straight and the last night of that week was when i experienced the EHS, which most likely was related to too much of an anti-cholinergic (not anti-histaminergic) effect. After that i learned to lower the Diphenhydramine dosage if taking it during active CYP inhibition, or taking it outside of the CYP inhibition at it's usual dosage, and all has been fine since.
Never had any issues with Cetirizine or Loratadine though, but again Loratadine should be reduced in dosage if taken during active CYP inhibition, but doesn't have to be reduced in dosage if taken outside of active CYP inhibition, and Cetirizine can be taken at the usual dosage because it's not metabolized by CYP's.
But yeah it's worth mentioning though that even if Diphenhydramine's potential Serotonin reuptake inhibition was noticeable, it's said to be weak inhibition, and the THH naturally found in Caapi vine is itself a weak Serotonin reuptake inhibitor and yet goes just fine with the reversible MAO-A inhibition of Harmalas. And ime THH is much more of a Serotonin reuptake inhibitor, than anything i've felt from Diphenhydramine, even with the Diphenhydramine was potentiated i don't think i really felt much in the way of any Serotonergic effects, in comparison i've felt way more Serotonin reuptake inhibition from THH. Theoretically if one were to take both THH and another weak Serotonin reuptake inhibitor, it could possibly potentiate it a little, but it just depends on how strong or weak an inhibitor is, but in Diphenhydramine's case, wouldn't be any issue with THH ime.
Also best to look at the properties of things via wikipedia and pubmed, rather than getting one's info from any Aya retreat sites.