Opioid receptors and opioid agonists are widespread throughout nature. Endogenous
opioids mediate complex functions in animals and in humans. The opioid system in humans
plays a central role in pain control and is a key mediator of hedonic homeostasis, mood, and
well-being. This system also regulates responses to stress and several peripheral
physiologic functions, including respiratory, gastrointestinal, endocrine, and immune
systems. The use of opioid medicine in the management of chronic pain has become …