Caffeine 101 | National Geographic

(light liquid pouring) (gentle sipping)

[Narrator] For morning coffee to afternoon tea, caffeine is so thoroughly entrenched in our daily routines and has become the world's most widely used psychoactive substance. Caffeine is a chemical compound that stimulates the central nervous system. It accomplishes this by attaching itself to adenosine receptors in the brain. In doing so, it blocks adenosine molecules, which are responsible for slowing down the central nervous system before we sleep.

The result? Adenosine cannot regulate and neurons start firing. This results in a person's reduced fatigue and increased alertness and cognitive performance. Side effects many seek by consuming caffeine. Caffeine occurs naturally in coffee beans, tea leaves, cacao beans and some tree nuts. People have been consuming it for centuries.

But daily consumption took off sporadically at different times in different places around the world. Coffee became popular in the 15th and 16th centuries. But cacao was used among early Mesoamerican civilizations hundreds of years earlier. Tea became popular by the 14th century in China during the Ming dynasty, but didn't catch on in Britain until almost 400 years later.

Today, caffeine can be found nearly everywhere and more and more caffeine-infused products are hitting the shelves every day. In the United States, nearly 90% of the population has at least one caffeinated beverage every day. Up to 400 milligrams of caffeine per day, or about four cups of coffee, is considered safe for an adult.

Too much caffeine for any one person can cause side effects, such as migraines, insomnia, nervousness and muscle tremors. One tablespoon of pure caffeine, equivalent to drinking 75 cups of coffee at once, can have lethal consequences. Due to this risk of caffeine overdoses, in 2018, the United States Food and Drug Administration banned the bulk sale of products containing pure or highly concentrated caffeine.

While caffeine may provide great benefits, such as increased focus, alertness and energy, it comes with considerable risks just like any other substance.