http://www.caffeined...dependence.html
Look here, it is possible to become dependant, but it´s rare and kind of contoversal still. If you start taking heroin(yes it´s different to caffeine and may sound hard, but it´s sort of model drug) you will become addicted to it in 100% and there is no way you wouldn´t, it´s just the way it works. All really addictive substances cause massive release od dopamine in brain, which cases that good feel, same works for food for example, BUT... Heroin does this so much more than common impetus like food, it is contraproductive and is causing harm to the brain tissue, so body tries to avoid this dammage by reducing number of dopamine receptors. This sure helps to prevent this "toxic" effect of dopamine, but it leads to lack of good feelings coming from those normal things like I mentioned before and that´s the reason why really addicted subjects need to take that drug, nothing else is strong enough and even the starting those is not enough for someone who has been on it for months or years. For someone who hasn´t tried it before, 300mg can be lethal, for experienced drug abuser is possible doing over 1000mg/day. Take him his dose and he may actually die in horrible pains, that´s why you can´t really stop taking without help of weaker opiates like metadon, you can´t take that pain. With caffeine, this doesn´t really happen, sure, you can feel weak, tired and not focused, but that´s about it, those two cannot even be compared.
And to add my personal experience as well, I have tried maybe 20 pre-workout supplements, all of them contained some form of caffeine in dosages much higher than cup of coffee and most of them contained some even more potent stimulans like geranium etc. I usually cycle usage of them and I can say I don´t feel any need to take any caffeine in this off window, not even one single coffee and I don´t feel any worse without them.