Cats love catnip because of the essential oil it contains: nepetalactone. This essential oil is found in catnip's leaves, stems and seeds. Catnip is an herb and a member of the mint family.
It's not completely understood why catnip stimulates cats, but researchers think that catnip acts as a happy pheromone while stimulating the receptors in a cat's brain that respond to those pheromones.
When cats come into contact with catnip, whether by sniffing or eating it, their entire personality changes for about 10 minutes. Cats on a catnip buzz roll on the floor, flip over objects, rub their faces in the catnip, meow and growl. Some cats become hyperactive and run around as if their tails were on fire, while others get aggressive and overly protective of their toys.
Researchers have found that the effect of catnip on cats varies based on how the cat is exposed to the herb. Cats that sniff catnip tend to demonstrate hyperactive effects, while cats that eat it tend to have the opposite effect and mellow out.
The effects of catnip usually last about 10 minutes. After that time, cats get bored with their toys and the catnip itself, and return to their normal behaviors. It takes up to two hours for cats to become sensitive to catnip again.