What Is Caffeine?

Caffeine (English: caffeine) is a xanthine alkaloid commonly found in the seeds and leaves of various plants, most notably in the coffee plant, tea plant, yerba mate (from the Paraguayan holly), and guarana. It also exists in smaller amounts in the cacao tree, kola nuts, and certain species of ilex used as herbal tea. When present in guarana, caffeine is sometimes referred to as guaranine, in yerba mate as mateine, and in tea as theine. Overall, caffeine acts as a natural insecticide in more than 60 plant species, paralyzing insects that feed on these plants.

Effects on the Human Body

Caffeine is a central nervous system stimulant that temporarily wards off drowsiness and restores alertness. People often consume caffeine during mental tasks such as studying, reading, or attending meetings to stay focused. Products containing caffeine—like coffee, tea, soft drinks, and energy drinks—are extremely popular, partly due to caffeine’s mildly addictive properties (sometimes referred to as “coffee addiction”). Caffeine is considered the most widely consumed psychoactive substance worldwide; in North America, 90% of adults consume caffeine daily.

Primary Sources of Caffeine

The world’s main source of caffeine is the coffee bean—the seed of the coffee plant—which also serves as the raw material for brewed coffee. The exact caffeine content of coffee depends largely on the coffee variety (species) and brewing method. Even beans from the same tree can vary significantly in caffeine levels. Generally, a cup of coffee can contain anywhere from 40 mg of caffeine (in an Arabica espresso) to 100 mg or more (in a strong espresso).

Dark Roast vs. Light Roast

Dark-roasted coffees typically contain less caffeine than lighter roasts because the roasting process reduces the bean’s caffeine content. Arabica beans also tend to have lower caffeine levels compared to Robusta beans.

Other Compounds in Caffeine Sources

Although coffee contains small amounts of theophylline, it does not contain theobromine. Many natural sources of caffeine also include other xanthine alkaloids, such as theophylline and theobromine—both of which can act as cardiac stimulants—as well as additional compounds like tannic acid.