Dark chocolate has higher % of cacao , the bean from which chocolate is made.
It's less sweet, doesn't have the milk of milk choc which has more fat and sugar
, in general. Cacao has theobromine and phenylethylamine /pea which have CNS enhancing or stimulant
effects, theobromine is like caffeine
. Pea ("love chemical") probably gets deactivated in the gut. Cacao has antioxidants , too.