Is the high similar to heroin/morphine etc in humans? Because if it is, then is catnip not addictive to a cat? What if a cat discovers whole fields of the stuff and decided to revel in it until death? It's unlikely but it could happen
Edit: twas a joke, guys...
Also, from the article: "Big or small, the felines surrendered to the substance, rubbing their heads and bodies in the patches for an average of 10 minutes"