Drewnowski found that eating chocolate causes the brain to produce natural opiates, which dulI pain and increase a feeling of well-being. If the receptors in the brain that signal the presence of opioids were blocked, chocolate bingeing decreased. It was not shown, however, if this was caused by the high fat or sugar content of chocolate candy. A little background information may help make this more understandable. A receptor is a structure on the surface of a cell that interacts with certain chemicals.
Receptors have different shapes, and thus interact with specific molecules.
Cannabinoids are substances that act like cannabis, also known as marijuana . There are chemicals in chocolate that act like THC, resulting in production of dopamine, a neurotransmitter. However, there is no THC in chocolate, so you aren't breaking the law by eating chocolate. One of the compounds in chocolate is anandamide, which is already produced in your brain. Well, anandamide is broken down quickly, so it isn't around long in your brain to make you smile.