I've just been reading online about anandamide and other endogenous cannabinoids, which are brain chemicals, naturally produced, that govern feelings of bliss and other sensations associated with cannabinoids.
That is to say, our brain produces anandamide and other endogenous (internal) cannabinoids all the time--it's a natural part of our biology.
Recently, chocolate has been found to contain chemicals that stimulate the anandamide and endogenous cannabinoid systems in the brain.
Here's a website providing more information about this:
http://antoine.frostburg.edu/chem/senese/101/features/anandamide.shtml
Here are a few citations about chocolate:
Brain cannabinoids in chocolate
E. di Tomaso, M. Beltramo, D. Piomelli, Nature, 382, 677-8 (1996). Coming: Drug therapy for chocoholics?
Science News, 147, 374 (1996). Chocolate may mimic marijuana in brain.
Chemical and Engineering News 74, 31 (1996).