Vet Blog has an explanation of why Hartz, Sargeant’s, and other cheap over the counter flea and tick prevention products are extremely dangerous. An excerpt:
Most veterinary products are designed act on nerve cells that only fleas or other arthropods possess. They therefore are very toxic to fleas and very non-toxic to mammals (although individual dogs and cats can react to the active or inert ingredients in any of the products).
Most cheap over-the-counter products contain pyrethrins or pyrethroids. These pesticides are toxic to just about every creature. Fleas and other arthropods are most sensitive. Cats are next. Then come dogs. Their margin of safety is poor. It is my opinion that these products are dangerous, period. …
The U.S. Environmental Protection Agency is pursuing a series of actions to increase the safety of spot-on pesticide products for flea and tick control for cats and dogs. Immediately, EPA will begin reviewing labels and determining which ones need stronger and clearer labeling statements. EPA will also develop more stringent testing and evaluation requirements for both existing and new products. EPA expects these steps will help prevent adverse reactions from pet spot-on products. EPA is coordinating with Health Canada and with the Food and Drug Administration’s Center for Veterinary Medicine on these actions.
EPA doesn’t name names, but I will. HARTZ and SARGEANT’S!
I wish EPA would ban these products. Sadly, that doesn’t seem likely. I urge you, in the strongest terms possible, never to use these products.