Caffeine is the most widely used drug in the world.
It takes coffee or tea about 15 to 30 minutes to have an effect on the brain, and about one hour to reach maximum blood levels. According to a recent study performed at Stanford University Medical School, anyone who consumes more than 500 mg. of caffeine per day may have a dependency problem. To give an idea of how easy it is to become dependent on caffeine, consider the following statistics. Loose black tea, brewed 5 minutes, contains about 150 mg. of caffeine, while a 10 oz. Green tea, frequently touted as an alternative to caffeine rich black teas, actually contains very nearly the same amount of caffeine as black teas.