YouTube: Over 100,000 metric tons of caffeine are consumed around the world every year. That’s equivalent to the weight of 14 Eiffel Towers! Caffeine helps us feel alert, focused, and energetic, even if we haven’t had enough sleep — but it can also raise our blood pressure and make us feel anxious. So how does it keep us awake? Hanan Qasim shares the science behind the world’s most widely used drug.