Catnip sensitivity is genetically linked. Very few cats in Australia have the gene for it (appx 30%), for example, because it didn’t grow wild there. No selective pressure for the gene.
Fun short list of things that can trigger the same reaction (and are perfectly safe) if they don't respond to catnip:
- Dried carrot
- Valerian root (in pouch)
- Silvervine
- Chlorine on swimwear/towels (try wet or dry)