I just wanted to make anyone using "zodiac spot on" aware of the difference between that and "frontline" or "frontline plus". The ads claim same active ingredient as frontline. Although it does contain methoprene, it is not at all like frontline. Methoprene: Methoprene is an IGR that does not directly kill adult insects but works on certain pests in their immature (egg, larvae) stages, thus breaking the cycle of infestations and preventing re-infestations. Immature pests exposed to this IGR simply cannot mature because they are over-loaded with a juvenile hormone mimic. If a flea larvae (for example) cannot reach adulthood, it cannot reproduce. Instead, the larvae simply dies in its immature stage. This is the active ingredient that both topicals share....... but, Zodiac also has permethrin at 45%..... This causes many more reactions than fipronal which is what frontline contains. Both these ingredients kill fleas......but permethrin is not as safe..... IMHO. Compare the ingredients: Zodiac:Active ingredients: permethrin 45%, s-methoprene 3%. Other ingredients: 52%. Do not use on puppies less than 6 months of age. Consult your veterinarian before using this product on debilitated, aged, medicated, pregnant, nursing dogs. Do not use on cats. Frontline Plus:Active Ingredients: fipronil 9.8%, (S)-methoprene 8.8%. Frontline Plus for Dogs is a monthly Topical Spot On treatment for fleas and ticks for dogs and puppies 8 weeks or older. I just want to make the point......... even though the Zodiac says.... "same active ingredient as frontline plus" You are not getting the same product....it is NOT the generic form of frontline plus..... the "other" active ingredients are DIFFERENT. And in my opinion it is worth spending the money to buy frontline plus instead of "zodiac spot on". Just something to think about......... Thanks, Julie.