Caffeine has been used by athletes for a long time as a performance-enhancing drug. Studies have shown that taking caffeine before exercise improves performance.

Caffeine is a stimulant and the most commonly used drug on the planet. What used to be a chemical only associated with coffee is now in chocolate, ice cream, weight-loss pills, energy and alcoholic drinks, mints, study aids, marshmallows, and non-prescription painkillers. Despite its universal acceptance and widespread availability, overdose is lethal — consumption of as little as a few grams can result in death.

Global population distribution:

Source: 1000 Genome Project. Global averages for both sexes