From Citizendium - Reading time: 1 min
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]