Our indoor cat all of a sudden had fleas, since it was a weekend and our vet would not be open until Monday(to buy advantage) we decided to go to the local pet store and get something for the fleas. We got her the Hartz flea colar. Within an hour of wearing it she became lathargic, unresponsive and developed a twitch. We immediately took her to emergency. The first thing the tech did when we got there was take off the colar and throw it away. She said she had seen several cats in there who had organ failure after using the colar or the drops. So after spending $320 for tests and antibiotics we are home now. Momo still isn’t the same a day later…she barely eats and sleeps all the time. They say it should get better but god only knows….This company should be put out of business!! We bought stuff for our puppy too from Hartz….its now in the garbage can unused.