Caffeine

Caffeine is an odorless alkaloid. It is a natural ingredient that is found in the green coffee bean. It is also found in a number of other plants, including tea, cocoa, kola, guarana, and yerba mate. Caffeine, used by people is the largest psychoactive stimulant, which speeds up the central nervous system.
Caffeine affects all of us differently. Where some might be able to fall asleep soon after drinking coffee, some might not.
Recent international studies have shown that caffeine has demonstrated protective effects against Parkinson’s disease and Alzheimer’s disease when consumed in moderation.
Caffeine enters your blood stream through the lining of your mouth, throat, and stomach. Your stomach contents can account for different effects of caffeine. It can take up to forty-five minutes for the majority of caffeine to be absorbed and the effects can last up to three hours.
A cup of coffee contains 98.6% water, which means 1.4% of that cup is dissolved coffee solids.  Caffeine is 1.2% of that 1.4% coffee.

Incidentally,  the US, drinks the most coffee, 400 million cups per day.