I used the Hartz Advanced Care 4+ treatment on my 5 year old Siamese on Thursday night. On Friday morning, he was twitching and shaking. I called my vet, told her what I had used, and acted immediately to give my cat a full body bath with something strong like Dawn dish detergent. My vet said the reaction to Hartz was very common and that they had seen much worse than my Beau was experiencing. In one case, they had to sedate a cat for a few days until the tremors wore off. Beau couldn’t sleep for 48 hours because of the tremors and was obviously in a lot of pain, but he didn’t stop eating snacks from my hand or taking small drinks of water. But I felt awful! I do everything for my cats but I was so ignorant about Hartz. Never again!