IRN-BRU Zero Sugar (or Sugar Free/Xtra) contains Carbonated Water, Citric Acid, Flavourings (with Caffeine, Ammonium Ferric Citrate, Quinine), Sweeteners (Aspartame, Acesulfame K), Preservative (E211/Sodium Benzoate), and Colours (Sunset Yellow FCF, Ponceau 4R), making it sugar-free, low-calorie, but with warnings about potential effects on children and containing a source of Phenylalanine.