Caffeine is a chemical found in the beans, seeds, leaves, or bark of many plants. Caffeine is considered a chemical stimulant of the nervous system. A chemical stimulant speeds things up both mentally and physically, increasing alertness, interfering with sleep, and raising heart rate and blood pressure.

Foods and beverages made from caffeine-containing substances are widely available in and accepted by most contemporary societies. In North America, the most common food sources of caffeine include coffee, tea, and chocolate. More than 80 percent of adults in North America consume caffeine regularly. Average per capita (per person) caffeine intake in the United States has been estimated at 211 milligrams per day, in Canada at 238 milligrams, in Sweden at 425 milligrams, and in the United Kingdom at 444 milligrams per day. The world's per capita caffeine consumption is about 70 milligrams per day.

A model of caffeine as produced by a computer. Drinking caffeinated beverages...