I suppose the key difference is that cats don't actually respond to ingestion or imbibing of catnip - the smell is the stimulant, and other plants like honeysuckle and valerian have similar effects. I suppose it's more comparable to aromatherapy than drug use - lavender is known to have a soothing effect on humans, while citrus smells are reviving and stimulating, as is ginger. We can of course eat some of these plants, but they are not drugs in terms of their aroma or digestion, they are simply substances that produce a (non-narcotic, non-psychoactive) emotional or behavioural response, though that response varies with each individual.
