I don't like the idea of it at all, personally. I'm not a fan of any injection that messes up your hormones. I can see it causing more problems in the long run. I would hope that a special tattoo would come with the injection, considering you'd have no way to really tell if the dog was spayed or neutered otherwise. Can you imagine if a dog got a double dose of this injection? Anyways, I feel that an injection powerful enough to render something impotent or infertile is a bit scary.