TABLE 1.

Opioid receptor families, their major functions, and associated endogenous agonists (52, 53).

Receptor family	Mu	Kappa	Delta
Functions	Analgesia Euphoria Physical dependence Respiratory depression Reduced gastric motility	Analgesia Dysphoria Reduced gastric motility	Analgesia Tolerance Anxiolytic
Endogenous agonists	Endorphins	Dynorphins	Endorphins