I am currently in college studying Veterinary Medicine. Hartz products are DANGEROUS. we specifically discussed that in class. They are known for making animals ill, and unfortunately–killing cats. Dogs can tolerate pesticides better than cats (even though it is dangerous for both). Harts flea and tick control products contain pesticides, Deadly for cats, dangerous for dogs. PERIOD. Hartz have many lawsuits against them, and they do need to be shut down. If you have any signs of adverse effects (which seems to always occur with EVERY Hartz products) discontinue use IMMEDIATELY. As a matter of fact, DO NOT USE IT AT ALL. Things that can occur are rash, itching, blisters, bumps, seizures,loss of appetite, fever, vomitting, etc. and even, unfortunately, death. If you need flea and tick control, for your pets sake, please use Frontline. It is the safest product, and Veterinareans number one choice for a reason.