Science, Tech, Math › Science Caffeine Chemistry What Is Caffeine and How Does It Work? Share Flipboard Email Print Caffeine is the most widely consumed psychoactive drug in the world. INDIGO MOLECULAR IMAGES LTD / Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated June 02, 2019 Caffeine (C8H10N4O2) is the common name for trimethylxanthine (systematic name is 1,3,7-trimethylxanthine or 3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione). The chemical is also known as coffeine, theine, mateine, guaranine, or methyltheobromine. Caffeine is naturally produced by several plants, including coffee beans, guarana, yerba maté, cacao beans, and tea. Key Takeaways: Caffeine Caffeine is methylxanthine that naturally occurs in several plants. It is related to theobromine in chocolate and the purine guanine.Caffeine is a stimulant. It acts by reversibly blocking adenosine from binding a receptor that causes drowsiness.In pure form, caffeine is a bitter, white, crystalline powder.Plants produce caffeine to deter pests and to prevent nearby seeds from germinating.Caffeine is the most widely used drug in the world. Here is a collection of interesting facts about caffeine: The molecule was first isolated by the German chemist Friedrich Ferdinand Runge in 1819. In plants, caffeine acts as a natural pesticide. It paralyzes and kills insects that attempt to feed on the plants. Caffeine also limits germination of seeds near the plant that could grow to compete for resources.When purified, caffeine is an intensely bitter white crystalline powder. It is added to colas and other soft drinks to impart a pleasing bitter note.Caffeine is also an addictive stimulant. In humans, it stimulates the central nervous system, heart rate, and respiration, has psychotropic (mood altering) properties, and acts as a mild diuretic.A normal dose of caffeine is generally considered to be 100 mg, which is roughly the amount found in a cup of coffee or tea. However, more than half of all American adults consume more than 300 mg of caffeine every day, which makes it America's most popular drug. Caffeine is generally consumed in coffee, cola, chocolate, and tea, although it is also available over-the-counter as a stimulant.Tea leaves actually contain more caffeine per weight than coffee beans. However, brewed coffee and steeped tea have approximately the same amount of caffeine. Black tea typically has more caffeine than oolong, green, or white tea.Caffeine is believed to aid wakefulness by blocking adenosine receptors in the brain and other organs. This reduces the ability of adenosine to bind to the receptors, which would slow down cellular activity. The stimulated nerve cells release the hormone epinephrine (adrenaline), which increases heart rate, blood pressure, and blood flow to muscles, decreases blood flow to the skin and organs, and causes the liver to release glucose. Caffeine also increases levels of the neurotransmitter dopamine.Caffeine is quickly and completely removed from the brain. Its effects are short-lived and it tends not to negatively affect concentration or higher brain functions. However, continued exposure to caffeine leads to developing a tolerance to it. Tolerance causes the body to become sensitized to to adenosine, so withdrawal causes blood pressure to drop, which can result in a headache and other symptoms. Too much caffeine can result in caffeine intoxication, which is characterized by nervousness, excitement, increased urination, insomnia, flushed face, cold hands/feet, intestinal complaints, and sometimes hallucinations. Some people experience the symptoms of caffeine intoxication after ingesting as little as 250 mg per day.The lethal ingested dose for an adult person is estimated to be 13-19 grams. In other words, a person would need to drink between 50 and 100 cups of coffee to reach the lethal dose. However, a tablespoon-sized amount of pure caffeine would be deadly. While generally considered safe for people, caffeine can be very toxic to household pets, such as dogs, horses, or parrots.Caffeine intake has been demonstrated to reduce the risk of type II diabetes mellitus.In addition to use as a stimulant and flavoring agent, caffeine is included in many over-the-counter headache remedies. Selected References Carpenter M (2015). Caffeinated: How Our Daily Habit Helps, Hurts, and Hooks Us. Plume. ISBN 978-0142181805Introduction to Pharmacology (3rd ed.). Abingdon: CRC Press. 2007. pp. 222–223.Juliano LM, Griffiths RR (October 2004). "A critical review of caffeine withdrawal: empirical validation of symptoms and signs, incidence, severity, and associated features" (PDF). Psychopharmacology. 176 (1): 1–29.Nehlig A, Daval JL, Debry G (1992). "Caffeine and the central nervous system: mechanisms of action, biochemical, metabolic and psychostimulant effects". Brain Research Reviews. 17 (2): 139–70.