The caffeine content of coffee beans varies according to the species of the coffee plant. Caffeine is also found in tea. In North America, the caffeine content of a cup of coffee averages about 75 mg, but varies widely according to cup size, the method of preparation, and the amount of coffee used. A cup of hot chocolate contains about 4 mg caffeine, and a 50-gram chocolate bar between 5 and 60 mg, increasing with the quality of the chocolate.
Caffeine is the world's most popular drug.
The white, bitter-tasting, crystalline substance was first isolated from coffee in 1820. The origins of the words reflect the spread of the beverage into Europe via Arabia and Turkey from north-east Africa, where coffee trees were cultivated in the 6th century. Coffee began to be popular in Europe in the 17th century. By the 18th century plantations had been established in Indonesia and the West Indies. Annual world consumption of caffeine is about 120,000 tons - equivalent to 70 mg of the drug a day for each inhabitant.