1. Introduction
Clinically, opioids are still the first choice for the treatment of
moderate to severe pain, the prescription of opioids for chronic pain
has increased in recent years. Despite their high efficacy in the
context of acute pain, opioids are associated with several troubling
side effects, including respiratory depression, reduced gastric
motility, and dependence/addiction. As a result, one of the
main goals of pain research is to identify compounds with similar
efficacy but fewer side effects.