Hello! Great question, with a mixed answer! Antihistamines are indeed quite useful in controlling the symptoms of an allergic reaction. Sadly to say, however, every antihistamine on the planet causes dry mouth (or makes it worse if you already have dry mouth). Overall, I would advise that the benefits of antihistamines in your situation outweighs the disadvantages. You can always use lozenges, drink plenty of water, or suck on ice chips to help with the dry mouth. You should not hesitate to go to the A & E if your symptoms should worsen. Too much mouth or throat swelling can cause serious breathing difficulties. For now, be sure to avoid amaranth exposure. Stay indoors if necessary. Again, drink plenty of water, and avoid strenuous activity until you are feeling better. I wish you the best, and a speedy recovery...