I ran out of Advantage flea preventative, so I tried Hartz 4-in-1. Since it was available in a pet store, I didn’t think it would be a problem. After applying to both of my cats according to the instructions, both cats experienced severe irritation at the site of application (neck). Within a few hours they were visibly mentally impaired. One of my cats could not even jump up on the sink. We had to take them to the vet, where they said they had experienced this problem before with Hartz products. They thoroughly washed both of our cats. Hopefully, this will remedy the problem, but I worry about what the long-term effects might be. This is a terrible product.