“Unlike dogs who tend to overindulge, cats will usually self-limit their play with catnip,” explains Dr. Whittenburg. “The only exception to this is typically catnip found in treats, which some cats will eat too many of if given a chance. With overindulgence of oral catnip, a cat may experience gastrointestinal issues such as vomiting or diarrhea.” You should seek veterinary help if vomiting lasts more than 12 hours or diarrhea lasts more than 24 hours.