Several more obscure chocolate ingredients seem to act by affecting the brain's own neurotransmitter network.

Neurotransmitters are the chemical messengers of the brain. They work by transporting electrical signals between nerve cells. These signals cause changes in the sensations and emotions that we experience.

Love drug?
Chocolate contains a natural 'love drug'. Tryptophan is a chemical that the brain uses to make a neurotransmitter called serotonin. High levels of serotonin can produce feelings of elation, even ecstasy - hence the name of the designer drug that also works by increasing serotonin levels.




http://www.bbc.co.uk/science/hottopics/chocolate/addictive2.shtml