I have a lot of friends that live out in "tickville", and their dogs have been on it since it came out, and they have all lived to be quite old, and what they died from was the usual heart/stroke/cancer that they died from back when they dipped them with some much nastier stuff. I don't have any real fears about it. I wish it had been available when I lived in Las Vegas, the ticks were amazingly bad out there, and my dogs would have to be dipped constantly. Flea collars were a joke, they just made the ticks move back away from their heads. I tried putting one on their tails too, just to see what would happen, and you can probably guess, the ticks just moved to the middle!