I needed to say something in hopes it helps someone out there that has no idea what is wrong with their dog....take the serestos flea collar off immediately! Two healthy dogs of my in-laws have just died because of this. The first was older and my in-laws thought she died due to old age. So they decided to put the serestos flea collar on their other dog because it was expensive and they had just gotten it. Well, immediately, this dog was getting sick, lethargic, no appetite...went to the vet numerous times (who also said the serestos flea collar was ok to use). The vet tried different things but could never really figure it out. They had no reason to think it was the dog collar. Well, it's too late now, but all the symptoms between the two dogs were exactly the same and both started when the collar was put on. We also researched it on amazon. For most dogs, the collar works perfectly fine....but not all. there is review after review on how this collar makes their dog sick (wish we would have researched it earlier). I am sick to my stomach that this happened, and am disgusted there is no warning on these collars. When I tried a search for serestos on this website, I was surprised to see nothing came up. (actually tried again and edited..it's seresto, not serestos). But if your dog is sick and you use one of these, its worth a try to take it off and see if that helps.