Guaranine is simply caffeine - called guaranine when found in guarana, mateine when found in mate, and theine when found in tea. A xanthine alkaloid found in the leaves and beans of the coffee tree, in tea, yerba mate, guarana berries, and in small quantities in cocoa, the kola nut and the Yaupon holly.

The world’s primary source of caffeine is the coffee bean (the seed of the coffee plant), from which coffee is brewed. Caffeine content in coffee varies widely depending on the variety of coffee bean and the method of preparation used, but in general one serving of coffee ranges from about 40 mg for a single shot (30mL) of arabica variety espresso to about 100 mg for strong drip coffee. Generally, dark roast coffee has less caffeine than lighter roasts since the roasting process reduces caffeine content of the bean. Arabica coffee normally contains less caffeine content than the Robusta variety.

Tea is another common source of caffeine in many cultures. Tea generally contains somewhat less caffeine per serving than coffee, usually about half as much, depending on the strength of the brew, though certain types of tea, such as black and oolong, contain somewhat more caffeine than most other teas. Tea contains small amounts of theobromine and slightly higher levels of theophylline than coffee.

Caffeine is also a common ingredient of soft drinks such as cola, originally prepared from kola nuts. Soft drinks typically contain about 10 mg to 50 mg of caffeine per serving. By contrast, energy drinks such as Red Bull contain as much as 80 mg of caffeine per serving. The caffeine in these drinks either originates from the ingredients used or is an additive derived from the product of decaffeination or from chemical synthesis. Guarana PMID 16533867, a prime ingredient of energy drinks, contains large amounts of caffeine with small amounts of theobromine and theophylline in a naturally occurring slow-release excipient.