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Caffeine belongs to a group of lipid-soluble compounds called methylxanthines. Together, caffeine and related substances such as theophylline and theobromine are naturally found in coffee beans, tea leaves, chocolate, cocoa beans, and cola nuts. Depending on the preparation technique, a serving of brewed coffee usually contains between 60 to 150 mg of caffeine, while instant coffee typically has about 60 to 100 mg of caffeine. Teas usually provide around 20 to 70 mg, and soft drinks typically have approximately 35 to 55 mg of caffeine. ^87,88