Catnip (nepeta cataria) is a perennial herb belonging to the mint family. There is a chemical present in its stems and leaves, nepetalactone, which causes a euphoric-type response in some adult cats, while young kittens are generally not affected.

"Approximately 30 percent of adult cats show zero or minimal response to the plant, and nearly all kittens under 2 months of age show no reaction to catnip and often actively avoid it," said Arnold Plotnick, DVM, owner of the Manhattan Cat Specialists clinic in New York.