My Golden Ret. (Jazzy and Jeter) are both on interceptor and now Mayzie is too. I live in PA and I have killed a mosquito in the house here during the winter so I don't take chances. We are on it all year round. It's expensive for my GR because one is 97 lbs and his sister is 87 - I split a box between the 2 every 3 months. The cost for theirs is 40 bucks a box. I am glad Mayzie's will be for 6 months and the smallest dose so I'm sure it will be cheaper. It is just not worth skimping on preventatives! If anybody finds a good place to buy interceptor online, I would be interested in knowing about it. I am not even sure if you can purchase it anywhere other than a vet--does anyone know?