I make catnip toys for our local Humane Society with homegrown catnip. Many of the commercial cat toys have so little catnip in them it is pitiful, mostly sawdust, I think. Ours is so good we call it Kitty Krack. Indeed, not all cats are sensitive to it, and they don't usually start to react to it until they are at least 6 months old. The active ingredient in catnip is very close to the pheromone a female cat puts out, which is why it is so attractive to cats (even females). Incidentally, the only other animal which reacts to catnip is the skunk. When I grow it, I have to put tomato cages around the plants or they would be flattened from every cat in the neighborhood rolling and sleeping on it. I make fleece cat beds for the Humane Society as well, and sprinkle a little dried catnip inside before I sew it up. That way the cat learns to love the fleece mat (we call them "cat hair catchers!"), and even after it is washed and the catnip pretty much dissipates, the cat is used to the mat and continues to sleep on it.