Warning: can make you dance like a lemon. Depletes your ceretonin levels and can leave you depressed for a few days afterward. Try things like banannas and 5HTP supplements (with proper inhibitors to prevent ceretonin production in the liver) to ease the effects, or if your lucky enough to be Dutch, "After E" available from smart shops. Can dehydrate you too, keep some water handy. And be sure of your source, there can be some nasty chemicals used in the production if the correct chemicals are in short supply. Best to get them before you go clubbing so you can check them out.
Many many clubbers out there