Endorphin

Endorphins are endogenous opioid biochemical compounds (peptides), substances produced by the body that resemble the opiates in their abilities to produce analgesia and a sense of well-being.

The term "endorphin" is used generally to refer to all of the endogenous opioid compounds and implies a pharmacological activity (analogous to the activity of the corticosteroid category of biochemicals) as opposed to a specific chemical formulation.

Endorphins have so far been found to be present only in vertebrate animals.

One theory of why some people find BDSM activities pleasurable is that these activities stimulate endorphins in a controlled way.