Many cats experience a euphoric sensation from breathing in the chemicals released by catnip, but dogs don't experience any effect. The herb contains a chemical compound called nepetalactone, which creates pleasant sensations for the majority of cats who inhale it. Whether they smell the air around catnip or eat it, though, a dog will not enjoy the experience like a cat does -- the nepetalactone has no effect on canines.
For Cats Only
Dogs aren't the only animals who don't experience an effect from catnip. Rabbits, mice and other species simply don't react to the herb like cats do. In fact, some creatures strongly dislike the nepetalactone found in catnip -- pests like mosquitoes and cockroaches are repelled by it. Dogs are simply unaffected by and indifferent to the herb, so you can let your cat enjoy it without worrying about harming or repelling your pooch.