Caffeine is a naturally occurring stimulant found in over 60 different plant species from cocoa and coffee beans to cola nuts and tea leaves. With billions of cups of coffee, tea and soda consumed each year, the world is wired on caffeine. Early civilizations discovered that plants containing caffeine had stimulating effects. Some considered these plants as sacred. Massive trade in tea and coffee over the centuries led to the global demand for caffeine. Whether it is harmful, helpful, or both is a subject of great debate.