Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Caffeine is a stimulant which is frequently consumed by humans and is found in popular beverages, foods and medicine. Moreover, it is the world's most popular psychoactive drug, used to improve mental alertness. Medics argue that moderate caffeine consumption has positive health effects, however, the addictive substance has also been linked to the development of various diseases. Learn more about the health effects of caffeine consumption in this book.