How much coffee is too much coffee?
Legend holds that kaffa, or coffee, was discovered in western Ethiopia by a man who noticed that his goats were more active after eating coffee beans. Today, caffeine is the most widely used brain stimulant in the world. Caffeine works by blocking another chemical in your brain, called adenosine, from bonding to receptors on your neurons. Adenosine is an inhibitor that keeps many brain regions in check, including one called reticular activating system, which basically amplifies brain activity. When adenosine is blocked, this region goes into overdrive, sending a wake-up call to the rest of your brain. So actually, coffee doesn't stimulate your brain. It just suppresses the part that makes you drowsy.
Is caffeine addictive? Some scientists think so. But it's not as bad as other drugs, because it doesn't strongly affect the dopamine pathways related to addiction. Your brain does learn to balance the caffeine though, which is why stopping cold can be a real headache.
And while the equivalent of a hundred cups of coffee can kill you, studies have found that in moderation, it may help protect against Alzheimer's and Parkinson's disease. So perhaps our craving for coffee isn't all that bad.