Caffeine

It is the only alkaloid used in the production of some foodstuffs. Caffeine is found in coffee and its metabolites: theobromine in tea and theophylline in guarana.
Caffeine causes an increase in secretion of, among others adrenaline, which stimulates the cerebral cortex, thought processes, shortens reaction time, increases concentration and eliminates fatigue.
By causing vasodilation, it improves heart function and increases vulnerability to physical exertion.
Caffeine is used primarily as a flavouring and energy additive in refreshing drinks.