A study of 13,000 people at University College London found that those that consume this food on a day to day have fewer depressive symptoms. It should be noted that this only happens with dark chocolate (the one that contains 75% or more of cocoa), not with any kind of chocolate.
According to research, chocolate contains psychoactive substances that produce a euphoria almost like that provided by cannabis use. Also, dark chocolate has phenylethylamine, which helps regulate mood. It also stimulates the assembly of oxytocin.