Caffeine addiction is something from which more people 'suffer' than would probably care to admit, because really we don't see it as an addiction. Nicotine dependence gives you cancer and emphysema; alcoholism gives you liver disease and driving bans; meth could result in a face different to the one you were born with.
Caffeine is humankind's favourite drug. It's estimated to be consumed by 80% of people worldwide, and most of us consume several doses a day. This popularity would appear to be explained in large part by caffeine's psychostimulant effect - starting the day with tea or coffee helps us wake up, and later on rescues us when our energy begins to decline.