I tried the topical flea treatment on my 10 lb Chihuahua/Jack Russell mix. For a day she seemed fine, but suddenly she became very ill. She was vomiting and having diarrhea. My housemate noticed blood in her stool, which was when I hurried her to a vet. They tested her stool to rule out parasites or bacterial infection, and the vet agreed it is most likely that the flea treatment made her ill. I was scared out of my mind; I’m lucky that she will be okay, but the medical bills and stress of my dog being sick was awful.