How old does a cat have to be to give them cat nip?

Answers:
not sure but it doesnt have the same effect on all cats.

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It can be given to a cat of any age, but usually only adult cats respond to it.

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Hmm, I dont know. I never introduced new born kittens to it...I have a older cat and he doesn't even notice catnip. So don't do what I did and go out to buy a giant tub of it : /

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Ok, instead of some boring read of an answer- i'm going to tell you the truth. 6 weeks is old enough to start. But let me ask you.. do you REALLY need/want... a really HIGH kitten ? Claws...teeth...insanity in and instant.
That... is something to think about.

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Because catnip is a natural plant, it doesn't have any bad effects on cats, no matter what age they are. I wouldn't give them a whole bunch at once though.

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Any age but some cats don't get high on it.