•In Shrek 2, guards capture Shrek and friends and one finds a bag of catnip on Puss In Boots' person. Puss denies that it's his. • The joke is repeated in Puss in Boots. Puss claims it's for his glaucoma.
A scene in Cats & Dogs 2: The Revenge of Kitty Galore has the heroes visit the house of a Crazy Cat Lady. Turns out a) cat ladies are such enablers for catnip addiction, b) cats on catnip act like comedic-variant stoners.
Catwoman has a scene where the titular character reacts very... strangely to catnip.
Played straight in the 'Fionna and Cake' episode of Adventure Time. Cake is handed a bag of catnip, and she sniffs it, after which her pupils dilate and she remarks, "SWEET BABIES..."