Theobromine is a major compound contributing to chocolate’s characteristic bitterness.
It is a naturally occurring alkaloid found in cacao beans and is chemically related to caffeine. Theobromine is present in cocoa solids, so dark chocolate generally contains more of it than white chocolate, which contains cocoa butter but no cocoa solids in the usual formulation.
The compound’s name comes from Theobroma, the cacao tree’s scientific genus; the name means “food of the gods” in Greek. Despite the similarity, theobromine is not the same chemical as caffeine, and their amounts and effects differ.
Theobromine is also important in veterinary safety. Dogs and some other animals metabolize methylxanthines more slowly than humans, so cocoa and chocolate products can be dangerous for them. That is why chocolate should not be treated as a pet food.