“…6,9,12 DOP receptor agonists may evoke physical dependence and convulsions, 6,13 whereas KOP receptor agonists are associated with dysphoria, sedation, diuresis, and hallucinations. 6 Based on their chemical structure, clinically used opioid analgesics belong to one of six main chemotypes, namely the morphinans (e.g., morphine (1), hydromorphone (3), hydrocodone (4), oxycodone (5), oxymorphone (6), codeine (7), nalbuphine (8), and butorphanol ( 9)), the orvinols (e.g., buprenorphine (10a), etorphine (10b), and diprenorphine (10c)) (Figure 3), the piperidines and anilinopiperidines (e.g., pethidine (11), loperamide (12), fentanyl (13), alfentanil (14), sufentanil (15), and remifentanil ( 16)) (Figure 4), the open-chains (e.g., methadone (17)), the benzenoids (tramadol (18) and tapentadol (19)), and oliceridine (20) (Figure 5). 7 Although opioid antagonists are also used clinically and in research studies, they are outside the scope of this Perspective.…”