When cats come into contact with catnip, they will release a chemical called nepetalactone, which can stimulate the cat's olfactory system and change the activities in many areas of the brain, thus making cats excited and hallucinating. This reaction usually disappears after 5 to 15 minutes, and will not cause any substantial harm to the health of cats.
Therefore, although catnip can make cats have an addiction-like reaction, this reaction will not cause harm to cats, nor will it really make cats addicted.