I think everyone is right here! Antihistamines can dry out mucous membranes, so that can include the GU tract, but as has also been said here, antihistamines are sometimes recommended for the management of interstitial cystitis. A very good BMS registered gynae who's fully aware of the problems of GSM & the various prescription treatments for it also recommended following a low histamine/histamine reducing diet for my longstanding IC & supplements with antihistamine properties such as quercetin. I think for women who suffer both bladder & vaginal symptoms it's a question of knowing a range of options we can experiment with, either individually or in combination, to find what works for our particular needs. Personally, to manage GSM & IC flares, as well as systemic HRT I use Vagifem with the weaker of the 2 estriol creams (0.01%) externally, as well as taking care with diet to limit those foods & drinks thought most likely to be problematic for bladder inflammation. I'm also currently trialling Sea Buckthorn, which I've not found very helpful in the past but I have some to use up in the fridge & a recent IC flare means I've needed all the help I can get!
Wx