You can overdose on caffeine.
Englishmen drink more tea than any person of any other nation (over twenty times more than Americans)
Chocolate is lower in caffeine than tea, coffee and coca cola. A one ounce bar of chocolate contains about 6mg of caffeine, whereas a five ounce cup of regular coffee contains over 40mg.
It has been shown that caffeine causes headaches when stopped suddenly and can cause morning headaches that are relieved by a dose of caffeine.