Caffeine: The Most Popular Psychoactive Drug

Caffeine blocks adenosine receptors, staving off the brain chemical that signals sleep. A cup of coffee delivers about 95 milligrams, absorbed within 45 minutes. Plants lace their leaves and seeds with caffeine as a natural insecticide. The compound was isolated in 1819 and now flavors energy drinks, fuels workouts, and anchors morning rituals worldwide..

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