There is a persistent urban legend that chocolate contains caffeine. It would seem that this rumor is based primarily on a confusion between two similar alkaloids: caffeine and theobromine. Theobromine is the active ingredient in chocolate and it occurs only in cacao. The two stimulants are related and have a similar structures, but are very different chemicals with different properties, effects and origins. There are of course, some chocolate products that have added caffeine, but it does not occur naturally in chocolate.