"Catnip" is the common name for a perennial herb of the mint family. It is native to Europe and is an import to the United States and other countries. The catnip plant is now a widespread weed in North America. Given to the right cat, catnip can cause an amazing reaction! The cat will rub it, roll over it, kick at it, and generally go nuts for several minutes. Then the cat will lose interest and walk away. Two hours later, the cat may come back and have exactly the same response. Because there really isn't any scent that causes this sort of reaction in humans, catnip is hard for us to understand. However, it is not an uncommon behavior in animals that rely heavily on their noses. For example, there are many scents that will trigger intense hunting behavior in dogs, and other scents will cause dogs to stop in their tracks and roll all over the scent. Although no one knows exactly what happens in the cat's brain, it is known that the chemical nepetalactone in catnip is the thing that triggers the response. Apparently, it somehow kicks off a stereotypical pattern in cats that are sensitive to the chemical. The catnip reaction is inherited, and some cats are totally unaffected by it. Large cats like tigers can be sensitive to it as well. The reaction to catnip only lasts a few minutes. Then the cat acclimates to it, and it can take an hour or two away from catnip for the cat to "reset." Then, the same reaction can occur again. Very young kittens and older cats seem less likely to have a reaction to catnip. http://science.howstuffworks.com/question303.htm

Catnip is completely safe, (it's a herb not a drug) and an excellent way of getting a lazy cat to exercise! Catnip tends to make the cat frisky & more active. Obesity is a serious problem in cats and cat nip is a great tool to use to fight against obesity. Some cats are never effected by catnip, even when full grown; however most cats, by the time they are 6 months old, can be effected by catnip. (Contrary to popular belief, catnip is nothing like marijuana nor is it anything like tobacco.) When not in use you should always keep catnip and catnip toys in air tight containers otherwise the catnip will go stale and will reduce/eliminate it's effectiveness.

Catnip (Nepeta cataria) is a perennial herb of the mint family. Although originally native to Europe, it has been successfully imported to many countries of the world where it is often considered to be a weed! The plant can grow as high as 3 feet, has lots of branches and can be recognised by its clusters of small white purple-spotted flowers at the ends of its stems.

Catnip contains various aromatic oils including one called nepetalactone, a mild hallucinogen, which is the main cause of the clinical signs. The receptor for nepetalactone is in the vomeronasal organ (also known as Jacobson's organ) at the back of the cat's nose and catnip needs to be inhaled to cause its effect. Indeed it is a great chance to see a cat exhibit what is known as the Flehmen response where it pulls its gums back from its teeth and almost looks as if it is smiling (see picture below, right). By doing this, the cat presses its tongue against the roof of its mouth forcing air through the vomeronasal organ. This concentrates the smell and allows the cat to concentrate the scent: to smell-taste, rather than just smell it.

 

When exposed to catnip some cats will rub (often with the chin and cheek areas), sniff, lick and eat the plant, sometimes followed by rolling over the plant. Following this contact with the catnip, behavioural changes are often seen. Most commonly reported signs of ‘intoxication' include having a ‘wild' or ‘drunken' appearance, vocalisation, rolling around in ecstasy and showing signs similar to sexual arousal. Affected cats look like they are having a really good time!! The effects usually last for a few minutes. Cats will then not react to catnip for at least an hour. In some cats, aggression can be seen with exposure to catnip. In these cats, it is probably best to avoid giving catnip treats or toys.

 

http://www.fabcats.org/behaviour/other/catnip.html