From the knowledge I’ve recieved working in the veterinary field, most flea & tick topicals should be used with caution on our pets. But, I have to say, I’m going on 5 years in this field and I’ve never seen one product alone cause sooo much harm and sometimes death as this product. When a person comes in with a pet with tremors and says the only thing that they have done different that day was apply a flea topical, they always look at us in amazement when we say, “Did you use Hartz by any chance?”. Please use the flea and tick control your vet recommends. Yes, I know it costs more, but from what I’ve seen, its worth every penny. I would never use Hartz on my 2 cats. I don’t know anyone in the vet hospital I work at that would either.