The manufacturers try to restrict the sale to only veterinarians, however, these are insecticides and are not under the FDA control. If Meriel, the manufacturer of Frontline finds a veterinarian reselling in bulk, they shut down the supply, however, they have not been successful overall. I don't know how it is being diverted, but it is. Almost all product sold by outside sources is branded for sale in the US. In the past, there was a lot of imported product that didn't have the EPA registration numbers on it like the US product. There has also been a lot of talk of counterfeit product, but I have never heard of any first hand, and I am in the trade....... Junk......