Chocolate contains caffeine and theobromine, between 0.6% (milk chocolate) and 1% (bittersweet chocolate), mainly in the form of theobromine (caffeine by itself would be approximately 0.1% and 0.15%). Caffeine, theobromine, and theophylline (in tea) are chemical compounds with closely related structures and similar pharmacological properties. All are members of a class of compounds known as methylxanthines, which occur in many common food plants such as coffee, tea, cocoa, and mate (a South American drink). Unlike caffeine, theobromine does not have a strong stimulating effect. The ratio of caffeine to theobromine in cocoa products is about 1 to 8. The caffeine and theobromine content of cocoa powder ranges between 1.5% and 2%.