ABSTRACT
The term “opioid” describes a wide range of compounds, encompassing the natural and semisynthetic opiates; essentially variations on a single structural theme as well as fully synthetic opioids with minimal structural homology to the natural alkaloids [1]. The defining characteristic of this class of drugs is their morphine-like antinociceptive activity stemming from interaction with opioid receptors, which play a major role in pain perception [2-5]. Other compounds that can be somewhat loosely referred to as “opioids” include receptor antagonists and mixed agonist/antagonists, as well as other opium-derived alkaloids such as papaverine that are not known to bind opioid receptors [6].
