The evidence of tape worms is very clear, or at least I've always found that it is. You will see small white pieces of the worm, which are it's back segments, moving as they come out of the anus or you may see them on the cat's fur. You will also find grains of what looked like dried rice in areas where your cats lie. I wouldn't medicate a cat for something that it shows no evidence of having. Also, tape worms don't pass from cat to cat so you only have to medicate the cat that has them (if any of them ever do).

I use Revolution because it works on ear-mites also.