We usually use Vectra 3D on our other dog, but the vet we are currently using doesn't have Vectra. However, Midge has never had a reaction to any flea product. We put the Frontline on Captain yesterday evening, and this morning he has diarrhea. I can't find any side effects listed besides irritation at application point. He is eating, and I gave him half a cup of pumpkin with his kibble. I feel bad, because I have him in the playpen in the kitchen, instead of out in the rest of the house (cream colored carpet!).