Choc, I know you mean well, but I think I have more experience with cats. Catnip may have a similar effect, but it doesn't cause brain damage or any kind of injury like human drugs do, especially when used properly.
What I suggested is the standard use of catnip, and it's completely safe, many people choose to grow catnip in their homes and let their felines nibble it as they please, which is not only healthy for the cat because it aids in digestion, but gives them a nice treat as well.
Like I mentioned before, I have owned a cat for 15 years, and she was very healthy all her life, catnip use and all.
5 bettas: Шостакович Shostakovich, Dimitri, Blood, Fancy Pants & Miss Priss; 1 cat: Rajah