Buyer Beware
Not every online pharmacy recieves their medication from qualified vendors. Without knowing it, you may wind-up giving your pet medication that is counterfeit or that comes from unkown sources. In the event of a bad reaction to these products, consumers are left without the protection of the vendors and pharmaceutical companies and are stranded by the online pharmacy.
The FDA statement for online pharmacies can be found here.
According to the Environmental Protection Agency, these products are packaged to look like the brand name product, but they are NOT approved by the EPA for use in cats and dogs. They are frequently missing the required package inserts that contain important product disclosure information. Many do not have child-safety seals and often what is advertised on the box is NOT what is in the box.