Simply put, caffeine is an alkaloid. These have several biochemical effects (eg, are easily oxidized to uric acid) and are found in common plant sources in different ratios.
Caffeine is present in coffee, tea, maté, cola nuts, and guarana plants, roughly to an extent of 4%. Caffeine stimulates the heart and respiratory systems while another alkaloid, theobromine (also found in tea) relaxes the smooth muscles.
Nowadays, caffeine is a common ingredient in several of the products we consume daily – from coffee and colas to chocolates and energy drinks. Scientists opine that caffeine in limited amounts is okay. But there is a flipside too – its psychoactive stimulant properties can lead to caffeine addiction which is as detrimental to health as other addictions can be.