Have you ever seen a cat play with a toy filled with catnip? If you have, you've probably seen some really funny feline antics.

Catnip is a fragrant plant from the mint family. Its scientific name is Nepeta cataria, and it's sometimes called "catmint" or "catswort."

Native to Africa, Europe and Asia, catnip can now be found all over North America, too. There are more than 250 species of catnip around the world today.

Catnip grows two to three feet tall and has sturdy stems with heart-shaped leaves. The tips of the plant's stems will sprout blue, white, pink or purple flowers.

Although catnip can have its effect when grown as a fresh plant, most catnip toys contain catnip that has been dried and ground into tiny pieces.

The leaves and stems of the catnip plant contain an oil called "nepetalactone." When cats smell nepetalactone, it stimulates special receptors that sense chemicals called "pheromones."

The result is a kind of chemical reaction that gives the cat a sense of euphoria or overwhelming happiness. The effect has been compared to that of a hallucinogenic drug on humans.

When cats smell catnip, they will often paw at it, rub it, roll over it, lick it and even chew it. Cats who have particularly strong reactions to catnip may also get frisky, meow, growl, purr, drool and generally act crazy for several minutes!

After a few minutes, though, the effect of the catnip wears off, and cats will ignore it. After about two hours, cats may encounter catnip again and have the same reaction.

Not all cats respond this way to catnip, though. Experts estimate about 50 to 75 percent of cats are affected by catnip. Young kittens and older cats are less likely to be affected.

Whether a cat reacts to catnip is believed to be hereditary, which means cats inherit this trait from their parents. For example, most Australian cats aren't affected by catnip.

Catnip has been shown to affect more than just house cats. Big cats, such as lions, tigers and leopards, react similarly to house cats when exposed to catnip.

Nepetalactone drives some cats crazy, but it can also drive mosquitoes, flies, cockroaches and termites away. Researchers have found that nepetalactone by itself is 10 times more effective than DEET, the ingredient in most insect repellents. Unfortunately, nepetalactone loses its repellent qualities when applied to the skin.

Catnip also has a long history of use by humans as a medicine. When consumed as a tea or infusion, it has soothing and numbing effects that act like a mild sedative. Humans have also used it from time to time to treat nausea, headaches and toothaches.

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