Pharmacology
Inside the body caffeine acts through several mechanisms, but its most important effect is to counteract a substance called adenosine that naturally circulates at high levels throughout the body, and especially in the nervous system. In the brain, adenosine plays a generally protective role, part of which is to reduce neural activity levels – for example, there is some evidence that adenosine helps to induce torpor in animals that seasonally hibernate.
Read more about this topic: Caffeine