According to a 2004 study in the UK, the amount of theobromine in a typical 2.5 oz dark chocolate bar works better than codeine to suppress the vagus nerve activity that triggers coughing.
In the study, participants were able to ingest significantly more capsaicin (the chemical that gives spicy chilies their kick) before coughing after they had taken 1,000 mg theobromine, when compared to those given a placebo.
Theobromine is one of the nervous system stimulants in chocolate. It dilates blood vessels, reduces blood pressure, increases heart rate and has a mild diuretic effect on humans*.
And apparently it’s also a cough suppressant! Sweet.
* Theobromine does not have such a pleasant effect on dogs. Be careful never to leave your chocolate out around dogs.