Theobromine
Also known as 3,7-Dimethylxanthine. Theobromine is structurally related to caffeine, and is one of the metabolites formed when caffeine is metabolized in the body. Theobromine is the primary alkaloid in chocolate/cocoa and also has stimulant effects, but is less potent than caffeine.
See “The Chemistry of Theobromine” for more information.