“My dog was on Frontline for years, it stopped working suddenly and we switched to this product and it worked great and there were no immediate signs of a reaction. My dog is 15+ now and has had tremors for about the past 8 years, so it could have come from the Frontline, hard to say but she now has a strange batting/squinting of her eyes and crouching her head anytime anything comes near her, even a fly or a bug. Could be from years of being on these flea meds but what can we do? Her quality of life is fine, she seems very happy just has some neurological issues but at her age, that could be age too. She is a 17 lb mixed terrier. I had another mixed terrier that was always on heartworm/flea meds and lived to be almost 20 and didn't have any of these particular symptoms so no telling”