Caffeine, also known as theine is an alkaloid wich comes in coffee-beans, tea and guarana for example. In the alkaloid-group are also cocaine and morfine.
Caffeine is a white powder with a bitter taste. That's why some energyshots and coffee taste bitter.
Caffeine is a stimulating substance. Caffeine is used in many products like Coca Cola and Red Bull, but also in painkillers. It is also used in fatburners, like the famous Stacker.
Caffeine raises the heartbeat and respiration. Caffeine raises the awareness, and stimulates the short-term. Learning and remembering is easier with some caffeine in your blood.
When you use caffeine often, you'll get used to it. You'll need more caffeine to achieve the same effect. You can get addicted to caffeine, and a sudden stop of taking caffeine can give you a headache and more withdrawal symptoms.
