Scientifically, nomenclature of the catnip plant is Nepeta cataria and it has an active ingredient known as Nepetalactone. Cats are known to have an extremely strong attraction towards this chemical, which is contained in the leaves and stems of the catnip plant. So if your cat happens to smell the herb, you will notice it exhibiting a variety of behavior which may be considered unusual at that point of time. These include growling, running, sniffing, chewing on the plant, licking the plant, rolling its head and rubbing its body against you. It is also common to notice your pet to shake its head, chin and cheek and drooling after it is exposed to the catnip plant. The plant may also have a sedative effect on some cats.
It has been observed that 2 hours post an exposure to the plant, the cat will become sensitive to another dose. However, not all cats get affected by the smell of the catnip plant. This is due to the fact that, the attraction which felines have for this herb, is genetic by nature. Meaning, 10-30% of the cat population does not show any kind of change in behavior even after being exposed to the catnip plant. Only felines who have inherited the genes, will be affected by the smell of this herb. Although your cat might exhibit all the above symptoms, it is to known that the catnip plant is completely non-toxic and harmless to felines. It might happen that your cat has consumed a large amount of the plant and is suffering from vomiting or diarrhea. But these conditions are rare and self resolving. Still, in cases of vomiting and the like, it is better to withhold the plant.