After our pets had skin reactions to the flea collars we switched to the drops. Within minutes both dogs were running through the house acting like they were on fire. We immediately took them outside and thoroughly washed the areas with dawn dish soap. Thinking it was again a skin reaction we gave them both Benadryl. One dog seem ok, the other became lethargic. When we picked him up he whined like he was in pain and was limp. We rushed him to the vet and were told that this was not uncommon at all. He was nearing organ failure. Thankfully after days at the vet he was able to come home. The vet told us drops are a terrible treatment and to avoid all Harts products.