Is coffee/caffeine addictive? I've heard that people get addicted. In other words, if someone has coffee regularly and they skip a day, then on that day they feel "low" or perform worse than they used to when they weren't a coffee drinker. Put another way, coffee no longer gives them a "boost"; rather, they need it to perform on par with when they weren't a coffee drinker. Is this true? What is your experience?

Any advice is appreciated. :)
Short answer is, yes.

This topic has been discussed a few times and mostly related to caffeine. Please see this previous question:


Can decaf coffee be addictive?


And, about being low after quitting coffee after a while... This is mostly relevant to caffeine withdrawal and discussed on this question: 


Why do I feel lousy, low, out of energy after the high coffee gives?