1.2. Caffeine metabolism. In the human body, caffeine is rapidly absorbed from the small intestine after oral administration into the body min and its average maximum value occurs min which directly depends on pH and can be prolonged by food intake. Its metabolic half-life - and it easily penetrates the blood-brain, caffeine and performance theses. Progressive delivery is highly recommended for your order. This additional service allows you to follow the writing process for large orders since the document will be sent to you for approval in partial drafts before the final deadline. A personal order manager. You can learn more about this service here or, Caffeine 1,3,7-trimethylxanthine is one of the most common substances used by athletes to improve their performance during competition. Evidence suggests that the performance-enhancing properties of caffeine can be achieved using several forms of administration, namely capsules, tablets, caffeinated energy drinks and,