Abstract: The present invention provides a composition for causing a simultaneous and synergistic increase in central nervous system activity and thermogenesis in a mammal, comprising Yerba Mate as a source of caffeine, hordenine and naringin. The present invention further provides a composition for causing a simultaneous and synergistic increase in central nervous system activity and thermogenesis in a mammal, comprising from 0.0001 g to 0.25 g of caffeine from Yerba Mate leaves, from 0.00001 g to 0.75 g of hordenine from barley and from 0.00001 g to 0.75 g of naringin sourced from grapefruit. The present invention finally provides a method for causing a simultaneous and synergistic increase in central nervous system activity and thermogenesis in an mammal prior to physical exercise, said method comprising providing a composition comprising a source of caffeine, hordenine and naringin and administering the composition to an mammal prior to physical exercise.