Catnip's primary active ingredient, nepetalactone, is similar to hallucinogens. However, it causes no harm to cats and does not turn felines into addicts. Some speculate that it triggers a sexual response; others believe the behavior more closely matches a cat's predatory reactions. Whatever the cause, the "catnip response" tends to last from 5 to 15 minutes. After the session is over, most cats won't respond to catnip again for at least another hour. Reproductive age cats tend to respond more than older or younger cats, and young kittens may actually avoid the plant.
For more information, please click on Why Cats are Crazy for Catnip.