I take maintenance allergy shots once a month and have to take an antihistamine before that. This is the only time I use an antihistamine because it dries me out so much that I am unable to clear mucus during airway clearance. My doctor said once on a webinar that mucus from a bronchiectasis patient is different from other people’s mucus. She also said that drinking more water, contrary to what you would think, does not help to thin that mucus. This is where the Guaifenesin comes in.