QUENCH WARFARE

Caffeine—a mild stimulant typically ingested in the form of coffee or tea but also consumed in caffeinated energy drinks and soft drinks such as Coca-Cola—is the world’s most popular mood-altering drug. Billions of people rely on it daily to boost energy and mental alertness and fend off drowsiness. It is also considered one of the world’s most benign drugs.

Unlike alcohol and tobacco, caffeine does not kill—at least not short of extreme doses equivalent to 60 to 90 strong cups of coffee for a 200-pound adult. Nevertheless, the drug has been complicit in plenty of killing. Caffeine has kept armies awake and alert, energized empires and rebellions, and otherwise helped to mobilize the world’s militaries. “When there is fatigue and the food is diminished,” U.S. Army brigadier general Michael Ryan Morgan observed in 1896, “such a stimulant is indispensable, and must be an ingredient of every reserve and emergency ration.”

Caffeine was first isolated in 1819 by German chemist Friedlieb Ferdinand Runge. Caffeine is certainly not unique to tea leaves and coffee beans— more than 100 other plants contain the alkaloid, including the guarana climbing vine, the kola nut, the yerba mate tree, and the guayusa holly tree—but