I have found that with my cat Dashiel that some cat nip is hit and miss with him. Whereas I have bought expensive brands and sprinkled it all over his scratching post and it has had no effect some cheap toy from the market with some in will have him in ecstasy for hours.
Although I like dried catnip and Dashiel seems to prefer it for convenience sake I find that catnip spray to be much easier not to mention cleaner to use with the only down side being that the effect doesn't last as long as with the dried stuff.

Like with the effectivity of the dried catnip some sprays are better than others and the Kong catnip spray is one of the better ones in my experience. It contains pure catnip oil and distilled water and is supposed to be all safe and natural.
The price for a bottle of the spray is £3.49 in my local pet shop and I find that the little spray bottle will last me a good couple of months before I have to buy a new one.

To use the Kong catnip all you need to do is spray a small amount on a toy, scratching post etc and then wait for your cat to catch the smell.
Dashiel gets excited as soon as he sees that I have the bottle in my hand and he jumps around my feet until I spray his toy or his bed and as soon as I have sprayed it he loses all interest in me completely and gives his undivided attention to whatever it is that I have sprayed.

His reaction to this catnip is slightly different to the dried catnip I also use. With the dried he goes a little wild but with this one his reaction is more calm and he seems to just enjoy rolling over it and giving it a little chew.
The only problem that I have with this catnip spray is that it just doesn't last that long. Dashiel will be having the time of his life but only for about half an hour before the scent must fade and he loses interest.

Because Dashiel enjoys this spray so much I have to give it quite a high score but I am deducting a star due to its longevity or lack off.