The stuff in tea and coffee that wakes you up is caffeine; caffeinated is the describing word. A caffeinated drink contains that stimulant. In ordinary talk it is the opposite of decaf: “Is this caffeinated or decaf?” Though actually it does not mean extra-strong — an ordinary cup of coffee is already caffeinated; it only tells you the caffeine is in there, not how much. Informally, of a person, caffeinated can mean buzzing, jittery, or comically lively from coffee. There is a verb too, to caffeinate. Packet English and café English use the adjective constantly; careful science writing may prefer “containing caffeine.”