Caffeine is a drug that we all experiment with from time to time. All thought we never think of it that way most people in America do have a caffeine addiction. Caffeine builds up in your system and makes you tolerant to it. You have to have it so the amount that is built up always stays the same. Considering that 80% to 90% of American adults consume caffeine daily and their daily caffeine intake exceeds 200 mg/day. With these facts it can be surmised that most of the U.S. adult population is completely tolerant and addicted to to most of the effects of caffeine.