Heres a pretty good article on Wiki about catnip

http://en.wikipedia.org/wiki/Catnip

-- it says theres about 250 different kinds of species of catnip (if i read it correctly), so I guess it makes sense that some will be stronger or different than others. I remember smelling some european catmint in a plant store and thinking that it didn't smell anything like the stuff I had at home.

I lucked out this year, and found a huge cache of catnip growing on the lakeshore near my house, so i cut and bundled it all up, hung it upside down in the garage to dry out -- i have 4 very large ziplock bags very tightly packed with catnip in the freezer right now, just waiting to be made into cat toys

The best part? Once you learn to identify the growing plant, you see it everywhere. Its the kind of plant that can grow almost anywhere, but you can usually find a lot of them in fields, ditches, etc. Since catnip is in the same family with the other Mints, it follows along the same lines -- all mints have a square stem with leaves evenly spaced on opposite sides up the stem (too one too many courses in wild edible plants *lol*).

Did you know too, that catnip is good for cramps if used as a tea? Its a mild muscle relaxant amongst other things. I've tried drinking catnip tea before, but its pretty strong. Not terrible if mixed with other mints though.