No conterfiet is not the problem in my case. Read this.
After a 20 month investigation in collaboration with (and initiated by) Bayer Animal Health,the EPA has "ordered retailers and distributors in a number of states to stop selling counterfeit Advantage products which falsely contain EPA registration numbers and labeling for Advantage." (Bayer Press Release) Merial, manufacturer of Frontline, has also been victimized, and is cooperating with the EPA investigation.
None of the material published by the EPA, Merial, or Bayer has indicated that the actual product inside the counterfeit packaging is counterfeit. However, the labeling may differ enough, and packaging may omit cautionary material, so that the wrong dosage may actually be used. It would appear that these counterfeit products have been repackaged in countries outside the U.S., relabeled to appear to be the genuine article, and then illegally imported back into the U.S. for sale to unsuspecting buyers. The relabelling (and often mislabelling) appears to be the real problem