Caffeine's use apparently dates back thousands of years - tea in China to 5000 years ago, Coffee beans in Africa to 1500 years ago, Coffee in Arabia to 800 years ago. Theophylline and Theobromine are also Xanthines. It occurs naturally in some plants nuts, seeds or leaves. This contains mainly theobromine. Natural usage of Caffeine need not be on the label.e.g.
Caffeine induces significant increases in cortisol, but no meaningful change in prolactin.
Caffeine's ability to antagonize adenosine receptors in the brain probably accounts for the most important of the drug's behavioral effects. Adenosine is an important CNS neuromodulator, possessing sedative, anxiolytic, and anticonvulsant properties. Adenosine also dilates blood vessels in cerebral and coronary circulatory networks. Caffeine competes with adenosine for binding at its high-affinity receptor sites, preventing adenosine's normal tranquilizing or sedating effects. Thus, caffeine's stimulant or anxiety-inducing actions appear to be secondary effects of adenosine antagonism.