Question: My seasonal allergies are intolerable, but antihistamines dry me out. Why?
Answer: Many patients may still have symptoms despite antihistamine use, even when it's causing dryness. Dryness is one of the more common side effects of the antihistamines.
And the other thing to remember is that antihistamines don't work for all the symptoms of allergies. So for congestion, in particular, if you're on an antihistamine that's drying you out, you may still be congested and still be suffering from allergies.