My 5 year old cat was given Hartz. Soon after, we took him to the vet because of weight loss and hair loss. They had no explanation for it. They said it was probably an allergic reaction and sent him home. Now it has been about a week or two and he’s gone into seizures and is vomiting frequently. My mother called the vet and they asked about medication or flea poison given to him in the past month. We told them we used Hartz and they said that is what has been causing it all along. I am so scared right now. He is the oldest cat we have and I hate to lose him. If anyone is thinking about getting Hartz, think twice. Talk to a vet to find out what kind of flea medication you need that won’t kill your pet. We will NEVER use Hartz products agan.