It is claimed that chocolate has the capacity to improve mood, and make people feel good. Chocolate is made from cocoa, butter and sugar. Milk chocolate contains extra milk solids and fats, white chocolate is akin to milk chocolate without the cocoa. That’s why white chocolate to my opinion is not chocolate. Attempts have been made to identify any psychoactive substance in chocolate. Several candidates were identified but their concentrations are too low to have a significant psychoactive effect and they are also present in higher concentrations in non-craved foods. Milk chocolate is the most preferred but if psychoactive substances were involved dark chocolate should be the most preferred. At least I prefer the dark chocolate.
Interaction between chocolate and neurotransmitter systems that contribute to appetite, reward and mood regulation were studied but no antidepressant mechanism of chocolate was found.
Chocolate can be the quality of chocolate graving, only chocolate will satisfy that craving. When experiencing an aversive mood state any carbohydrate will suffice in an attempt to achieve relief. This last form of behavior is also called emotional eating, food preference can be altered across a range of mood states. It is useful to distinguish between these two separate phenomena: chocolate craving and carbohydrate craving. The two phenomena can, however, co-exist in the same individual by virtue of the dual status of chocolate as being specifically desired and being more generally craved as a carbohydrate at times of emotional eating.
For most people chocolate is a substance of pleasure and extravagance. When taken in response to a dysphoric state as an emotional eating strategy it may provide a transient comforting role but it is more likely prolonging this state. It is not an antidepressant.
For an excellent review please read: Mood state effects of chocolate.
Parker G, Parker I, Brotchie H. J Affect Disord. 2006 Jun;92(2-3):149-59.