Endorphin molecules binding to receptors, illustration - stock illustration

Endorphin molecules binding to receptors, illustration. Endorphin molecules (red) binding to the delta opioid receptor (purple) on a cell membrane (blue). The endorphin shown here is met-enkephalin, also known as opioid growth factor (OGF). The opioid receptors play a role in modulating pain perception. Opioid agonists are potent analgesics that are produced mainly in the brain and spinal cord. The endogenous (produced in the human body) opioid types are enkephalin, dynorphin, endorphin and nociceptin.