Cocoa / chocolate is derived from the seeds of the theobroma cacao tree (cocoa beans). Chocolate contains caffeine, but higher amounts of theobromine, an alkaloid in the xanthine family. Theobromine is classified as a mild central nervous system stimulant and has physiological effects similar to those of caffeine, but seemingly weaker. The average cup of hot cocoa contains about 10 mg of caffeine and over 200 mg of theobromine. A 3 1/2 ounce (100 g) semi sweet dark chocolate bar contains about 12 mg of caffeine and 155 mg of theobromine.