Why do cats go crazy over catnip?
by KittyKondo.com

Many cats love catnip and will go "crazy" whenever they are near it. This is because catnip, also known as "nepeta cataria" or cat mint, contains the chemical called "nepetalactone". Nepetalactone is a mild, hallucinogenic substance that causes excitatory short-lived reactions in cats. Although catnip is a hallucinogen it is non-addictive and harmless to cats and kittens.
   Cats will become actively playful, roll over and chew when exposed to catnip; however its important to know that not all cats and kittens will have this reaction. About 50% of cats actually don't respond to catnip and kittens who are under 8 weeks of age cannot respond.