This is Why Cats go Crazy for Catnip!
There is a chemical in catnip which your cat's brain detects and produces endorphins in their brain which are the bodies natural "feel-good" hormon...
The Plant that is an Alternative to Catnip!
I remember having cats in the past who just were not "into" catnip like some others were. You might have a cat who is the same... turns out as man...