Caffeine is a stimulant found in many plant species. The most common natural sources of caffeine are coffee, tea, and cocoa, although the last one contains very low amounts in comparison.

Although the amount of caffeine varies according to brand and method of preparation, coffee is, without a doubt, one of the most popular natural sources of caffeine. A six-ounce cup of instant coffee contains about 60 milligrams of caffeine, while the same amount of automatic-drip coffee contains around 140 milligrams (mg). Tea, another of the most popular natural sources of caffeine, can also have varying amounts of the substance. Green tea is the lowest, with only 35 milligrams per six-ounce cup; black tea can contain up to 75 milligrams, depending on brand and country of origin.

Cocoa is one of the healthiest natural sources of caffeine. One ounce of baking chocolate contains about 25 mg of caffeine, but a glass of chocolate milk barely reaches five mg.

Natural sources of caffeine also include yerba mate and guarana, two South American plants that have only recently become known around the world. Guarana is a popular soft drink in Brazil, but in the rest of the world, it is basically used as an add-on to energy drinks. Guarana contains more milligrams of caffeine per ounce than coffee does. A typical energy drink made with guarana can contain as much as 259 mg of caffeine.

Yerba mate is one of the most popular natural sources of caffeine in subtropical South America, especially Argentina and Paraguay. Yerba mate leaves can be used to make an infusion that resembles green tea, although much stronger. Yerba mate has about 50 mg of caffeine per six-ounce cup.

The kola nut, a native to tropical Africa, is one of the popular natural sources of caffeine among West African cultures. The kola nut is usually chewed or roasted for use in some traditional drinks.

Excessive caffeine ingestion can cause insomnia, anxiety, gastritis, and an irregular heartbeat. All artificial and natural sources of caffeine should be reduced during pregnancy. Withdrawal symptoms are common among people who have been consuming large amounts of caffeine and decide to stop abruptly.