Something like 90% of Americans consume caffeine in one form or another every single day. More than half of all American adults consume more than 300 milligrams (mg) of caffeine every day, making it America's most popular drug by far. The caffeine comes in from things like coffee, tea, cola, chocolate, etc.

Have you ever wondered what it is that makes caffeine so popular? What does this drug do that causes its use to be so widespread? In this edition of HowStuffWorks, you will learn all about caffeine.