This scientific text explores the molecular pharmacology of caffeine in the human body, detailing how this widely consumed substance impacts physiological and neurological functions. It explains caffeine's absorption and metabolism, highlighting the role of the CYP1A2 enzyme and the formation of active metabolites like paraxanthine, theobromine, and theophylline, while also discussing individual metabolic variability. The primary mechanism of caffeine, adenosine receptor antagonism, is thoroughly described, including its structural mimicry of adenosine and subsequent effects on neurotransmitters like dopamine and norepinephrine. Finally, the document examines secondary molecular mechanisms that occur at higher caffeine concentrations, such as phosphodiesterase inhibition and intracellular calcium mobilization, alongside the molecular adaptations the body undergoes with chronic caffeine consumption, leading to tolerance and withdrawal.