There can be quite a dilemma when comparing products based on their labeling alone. While it seems that the active ingredients are similar or even the same (Frontline vs other products containing fipronil) I have found most of the time the inactive ingredients or carriers for the product are where problems arise. I have tried many of the OTC topicals and skin irritation or problem residues are consistent issues with "knockoff" products. Also there are frequent examples of OTC products that actually have higher risks for side effects and toxicity than presecription products, the example being the many high dose permethrin fleas and tick products available OTC. For oral flea and tick products the OTC offerings are not even the same active ingredients. As a veterinarian I use products for my pets and recommend products for my clients that I am confident about safety, efficacy and ease of use. As examples I cam currently using ivermectin based heartworm products and Bravecto for my dogs and Frontline for my cats.