I'm a huge fan of tea. I got this gluten free, vegan hippie chick at work that's all about the herbs. She hooks it up with the Kava tea. 
haahhaa..'
For the longest time, we didn't know WHY people drank tea/ coffee, but now we do know.. They're actually getting a short duration high.
It's not intense enough to haywire a person like a hardcore drug, but the long term effects are quite similar.
That being, Shortening natural attention span, higher probability of depression, lower inhibition, larger emotional swings.
Now i know why the English are so cynical...
Hahaha....
If we look at the natural progress in terms of individual motivation. Our system always chases the high, be it from food, sex, or something extreme like drugs.
All of those things in large enough quantity results in distortion of the person's mental balance and (drive) circuit.
Food, obesity, food addiction
Sex, sex addiction
Drugs, alcohol....
They're all different paths that operate the same optimizing function.
Why the problem occurs is because we're SO DAMN GOOD at being HAPPY due to modern technology.
Yet, our biological brain is INCAPABLE, and not equipped to handle how happy more specifically how (quickly happy) we can make ourselves