Caffeine Caffeine is the psychoactive substance most consumed by humans worldwide (Reid, 2005). This report details its natural origins, chemical structure (as well as that of similar substances), methods, and dosages in which it is rendered into its usable form. Additionally, this report will detail caffeine's various biological pathways within the human body, including access to the brain and various neurotransmitter pathways. Caffeine is a chemical that occurs naturally in over 100 plant species worldwide (Steffen, 2000). Perhaps the best known of these plants is the coffee plant, whose small seed (commonly called a “bean”) is roasted and then crushed into a fine powder (Weinberg and Bealer, 2001). Caffeine is also found naturally in cocoa beans, tea leaves, kola nuts, gurana seeds and mate. Some of these plants, such as tea, actually contain a distinct, but similar chemical to caffeine (i.e. theophylline); these chemicals will be discussed further in the chemistry section (Steffen, 2000). Caffeine is chemically known by two names. The first is 1,3,7-trimethylxanthine; the second is 3,7,-Dihydro-1,3,7-trimethyl-1H-purine-2,6-dione. Historically, in addition to caffeine, caffeine has also been called methyltheobromine (Weinberg and Bealer, 2001). The chemical formula of caffeine is C8 H10 N4 O2. The molecular weight of this chemical is 194.19 atomic units. Its composition is as follows: 49.5% carbon, 5.2% hydrogen, 28.9% nitrogen and 16.5% oxygen. Caffeine dissolves from a solid hexagonal crystal at 238 degrees Celsius (Karch, 1993)....... center of the article...... Parliament, C.Ho and P.Schieberle(eds) , Caffeinated Beverages: Health Benefits, Physiological Effects, and Chemistry (p.46-53). Washington, DC: AmericanChemical Society.Spiller, G. (1998). Basic metabolism and physiological effects of methylxanthines. In G. Spiller (ed.), Caffeine (p.225-231). New York: CRC Press. Steffen, D. (2000). Chemistry and health benefits of caffeinated beverages: Symposium overview. In H. Parliament, C. Ho and P. Schieberle (eds.), Caffeinated beverages: health benefits, physiological effects and chemistry (p.2-8). Washington, DC: American Chemical Society. Reid, T. (2005 ). Caffeine: what's the problem? Why we love caffeine. National Geographic, 207, 1, p.2-33. Weinberg, B., & Bealer, B. (2001). The world of caffeine: the science and culture of the most widespread drug in the world. New York: Routledge.