Caffeine is a bitter white alkaloid that acts as a psychoactive stimulant drug and a mild diuretic (speeds up urine production).

Caffeine was discovered by a German chemist, Friedrich Ferdinand Runge, in 1819. He coined the term "kaffein", a chemical compound in coffee, which in English became caffeine.

Caffeine is also called guaranine when found in guarana, mateine when found in mate, and theine when found in tea; all of these names are synonyms for the same chemical compound.

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