Caffeine is a widely used stimulant found naturally in coffee and tea and added to everything from energy drinks and sweets to medications. People turn to it for energy and focus, from shift workers, long-haul drivers, and doctors to office administrators and those with attention problems like ADHD. But because it's unregulated and so common, many of us have forgotten that caffeine is a drug, and like all drugs, it affects our health whether we realize it or not.