ffeine is allowed in moderate amounts. Caffeine is one of three different xanthine derivatives. The other two, theobromine and theophylline, are found in cocoa and tea, respectively. All three drugs produce similar physiologic effects (11:435-436).
Upon consumption, xanthine derivatives are completely absorbed from the gastrointestinal tract. They then diffuse throughout the entire organism; their distribution correlates closely with that of body water. In particular, the compounds achieve their highest concentrations within skeletal muscle (9:215-219). In addition, the xanthine derivatives are highly lipid soluble, and readily cross the blood-brain barrier. This is thought to occur both by diffusion and also by a saturable transport system (8:139-155). Peak blood levels usually occur within approximately 30 to 60 minutes (11:435-436). The brain concentration of caffeine may then remain stable for at least an hour (8:139-155).
Moderate doses of caffeine act as a "mild stimulant (8:139-155)." The drug is primarily used for the relief of minor fatigue. Moreover, while there are few adverse effects associated with caffeine, ingestion of excessive quantities can result in death. The lethal acute dose for an adult is between 5 and 10 grams (i.e., the amount found in about 75 cups of coffee) (8:139-155).
The use of caffeine to improve athletic performance was suggested during the 1950s. Although some studies have shown that the drug improves endurance, the hypotheses remain controversial. Despite the ongoing debate though, many athletes are convinced of caffeine's positive effects. Therefore, urine caffeine concentrations are currently monitored and controlled. The maximal concentration allowed by the International Olympic Committee is 12 micrograms per milliliter (10:225). For any given steady state caffeine intake, there is considerable variability among different individuals as far as both urine and plasma conc...