Watch the buzz in energy drinks. While they may tout "natural" ingredients like amino acids, or B vitamins and exotic extracts like guarana and ginseng, the "energy" in most energy drinks, scientists suspect, comes from a very familiar source: caffeine—sometimes in doses twice as high as you'll find in a regular cola. While brands vary widely—and so do people's tolerances for caffeine—know that you're likely getting a java-like jolt in every sip you take.
