Summary Caffeine: physiological and pharmacologic aspects Ugeskr Læger 2004;166:2138-2142 Caffeine is the most widely used stimulant in the world. This is due not only to the fact that it is found in a great number of food products and is therefore readily available, but also because caffeine intake results in such positive effects as elation, pleasantness and better reactivity and because abstinence from caffeine can result in a withdrawal syndrome including headache, tiredness, restlessness and heart palpitations. Caffeine is also used in sports, as caffeine in moderate doses (3-6 mg/kg) can increase the endurance of athletes engaged in running, bicycling, swimming and other endurance sports. Caffeine is used both in training and in competitions, and the International Olympic Commitée (IOC) has included caffeine as a drug used for doping. There are several theories about caffeine's mechanism of action. The most likely and most recognized is the adenosine antagonist receptor theory, but it is also possible that caffeine exerts its effects through a different mechanism.
Ugeskrift for Læger, 2005, Vol 166, Issue 22, p. 2138-2142