I bought Hartz Ultraguard for My cat who is about 10 months old, I’ve only had him for five days. It seemed like a good deal because frontline and advantage looked so expensive. After trying to make sure he didn’t lick until it was dry(he did a little), he started to scratch a lot. I thought it was just the fleas dying or Hartz doing its job. Then he threw up in the living room and had diarrhea, thankfully in the litter box. I called the emergency vet and was told how horrible Hartz is and to wash it off immediately and that I would still need to watch him throughout the night because it’s known to cause death in cats. It was only on him for a few hours and I’m really hoping that I got it off in time.