How Catnip works
Science of catnip
Catnip contains nepetalactone. Some cats are born with a catnip gene which makes them go bonkers when they are exposed to the plant. Other cats do not have the gene, so they have no reaction. Some cats are born with two of the genes, which makes them go nuts with several types of mint plants, not just catnip.
The chemical does not cause any effect by injection or ingestion, but rather works its magic by scent. When a cat chews or claws at the plant, an odor is released. This odor triggers a chemical reaction in the brain producing a "high" that can last up to 40 minutes. After the reaction is complete, the brain chemical is depleted for 1 hour. In this time, the nepetalactone will not have any effect.
Catnip is completely safe and non-addicting. It actually aides in digestion and anxiety in cats and many other mammals, including humans.