My beloved 9 year-old poodle, Tootsie, had Hartz put on her neck, by me, to get rid of fleas. Within a couple of hours, she was throwing up and didn’t even feel like getting up from the floor to walk around. Also, when I put it on her, she twitched a lot at first. She was sick for about 24 hours after putting on the flea treatment. NEVER AGAIN.