Caffeine is made of carbon, hydrogen, nitrogen, and oxygen. Interestingly the same is true of cocaine and heroin.
More than 80% of the world’s population consumes caffeine in some capacity every day. This occurs generally via coffee, tea, or soda of some sort.

Milk chocolate has more than 150% of the caffeine in one serving of Coca Cola.
A lethal dose of caffeine is difficult to precisely quantify for each individual. Suffice to say it is about 50 espressos.
Birch control pills can extend the half life of caffeine, thus placing more importance on monitoring intake if using birth control pills.

Ferocious debates swirl around the benefits versus risks of caffeine and coffee, tea, and soft drinks. One can often find conflicting signals. Here is some recent research discussed in the NY Times.

Check out an informative post on interesting facts about Coca Cola here.