Too much caffeine will also put you at risk for caffeine-withdrawal headaches when you stop it. Many of us who work in high-frenzy professions do or used to drink coffee constantly, all day long. I used to do that. But then I found that I was experiencing horrendous migraine-like headaches on the weekends. We finally connected the dots, realizing that I drank coffee all day during the week, but not on the weekends. When I reduced my workday caffeine intake, the weekend headaches went away.
Years later, while I was still drinking coffee at this "reduced" level, I began to experience consistent twitching muscles around one eye. I saw my ophthalmologist and asked him what causes the twitch. He said that they really don't know what causes it, but that many of his patients who experience such a twitch had found that if they stop caffeine, the twitch went away. I tried this - totally stopping caffeine. My twitch went away. It has been about 10 years now, and I do allow myself small amounts of caffeine now and then (like one glass of cola), and no more twitching.
These are just anecdotes, but I think they demonstrate that caffeine, in excess, can cause a lot of strange things to go on. Probably each of us has their own "threshold" so that they can tolerate some caffeine without effect, but if they go beyond that, something goes wonky.
