My horse started coughing once it got warm in my area. I tried AniHist for him, but it did absolutely nothing and the cough continued to worsen. After having my vet check him out and talking it over with her, I stopped the AniHist and switched to Cough Free and watering his hay. He stopped coughing almost entirely within 3 days
ETA: 99.9% sure it was allergies in my horse's case.