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Caffeine, contained in coffee and other drinks, is a mild stimulant and "is the most widely used psychoactive drug in the world."[1] It is a member of the class of methylxanthines, also containing theophylline, theobromine, and aminophylline, which have similar but not identical actions (e.g., relatively more or less stimulation and bronchodilation).

Cessation of caffeine intake can lead to withdrawal symptoms.[2]


Caffeine competitively antagonizes adenosine receptors. This antagonism prevents adenosine's inhibition of intracellular cyclic AMP. Cyclic AMP is a second messenger that increases sympathetic stimulation and increases norepinephrine and dopamine release[1]


  1. 1.0 1.1 O'Brien, Charles (2006). “Chapter 23. Drug Addiction and Drug Abuse”, Keith Parker; Laurence Brunton; Goodman, Louis Sanford; Lazo, John S.; Gilman, Alfred: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 11th. New York: McGraw-Hill. ISBN 9780071422802. 
  2. Silverman K, Evans SM, Strain EC, Griffiths RR (October 1992). "Withdrawal syndrome after the double-blind cessation of caffeine consumption". The New England journal of medicine 327 (16): 1109–14. PMID 1528206[e]