Catnip is completely safe for kittens, but they do not usually respond to it until at least three months of age due to their genetics, according to WebMD. Sensitivity to catnip is an inherited trait which typically starts to show between 3 and 6 months of age. However, some cats never receive any effect from the herb.
Catnip is an herb in the mint family, and it has an active ingredient in the leaves, seeds and stem called nepetalactone. Catnip causes cats to enter a state of euphoria, and they are often seen rolling around crazily, playing wildly or lounging lazily. These effects typically only last about ten minutes, and it may be several hours before additional uses of catnip will trigger a similar response. Despite how cats react to it, catnip is non-addictive and safe for them to eat.
For those cats predisposed to catnip sensitivities, it is a powerful training tool. Rubbing catnip on scratching posts or toys, deters a cat from scratching on unwanted items and encourages her to focus on items containing the catnip.