I also had an issue with hartz ultra guard. I thankfully purchased the collar and was able to take it off of her right after I noticed her acting weird. I put the collar on my 6 month old shih tzu an hour before dinner. I fed her dinner and she threw all of it up. I talked to my mom and did some research and I am throwing this collar away now! Only thing is my puppy still has stiches in from getting spayed and Im not sure if the groomer can apply a flea and tic treatment. I hope taking the collar off solves the problem and she is back to her normal self.