Coffee contains caffeine, a mild stimulant. Drinking coffee results in an increase of the heart rate of the drinker, increased blood flow to the muscles, and an increase in blood pressure and it causes a decrease in blood flow to the skin and to the inner organs. Most importantly for many drinkers, the level of dopamine in the brain increases.
The tea bush originated in the area where India, China and Myanmar meet, in the hot wet mountainous regions of the Eastern Himalayas. It was originally eaten and drunk by tribal groups in this area. Over two thousand years ago it was used as a medicine and aid to concentration in China, being helped by the expansion of Buddhism from India.