what is caffein
Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class of psychoactive drugs. It is the world's most widely consumed psychoactive drug, but unlike many other psychoactive substances, it is legal and unregulated in nearly all parts of the world.he world's primary source of caffeine is the coffee bean (which is the seed of the coffee plant), from which coffee is brewed. Caffeine content in coffee varies widely depending on the type of coffee bean and the method of preparation used; even beans within a given bush can show variations in concentration.