My vet stopped selling the flea medication my dogs took orally so I purchased the Hartz medication over the counter until I could order her medicine online. Upon administering the proper dosage on her she started acting strangly.. She walks around in circles and it looks like she is hallucinating. She jerks her head and wines while she is losing strength in her rear legs.. The vet said she is having seizures. He said she is having a bad reaction to the Hartz flea medication.. If it dosen’t stop within a week, she needs to see a specialist. I’m afraid she will die, especially after reading some of these horror stories. Something needs to be done about this.. It’s terrible when you are trying to protect your dogs from fleas and you end up maybe killing your dog. I can’t beleive there isn’t a class action suit against Hartz.