Caffeine is a naturally occurring alkaloid and a central nervous system stimulant found in coffee, tea, cocoa, and several other plants. Chemically, it belongs to the xanthine class and acts by blocking adenosine receptors, which promotes alertness and reduces fatigue. The use of caffeine-containing beverages dates back thousands of years: tea was consumed in China around 2737 BCE, and coffee use became popular in the Arab world in the 15th century, eventually spreading to Europe by the 17th century. Isolated for the first time in 1819 by the German chemist Friedrich Ferdinand Runge, caffeine has since become one of the most widely consumed psychoactive substances in the world, used not only in beverages but also in medicines, energy drinks, and food products. Its historical and cultural significance, along with its physiological effects, has made caffeine a subject of both scientific research and daily human consumption.
