Fentanyl Analogs, Other Synthetic Opioids, and Research Opioids
"Opioids are a group of drugs comprising a range of substances, including opiates and their synthetic analogues. Opiates are the naturally occurring alkaloids found in the opium poppy and include morphine, codeine and thebaine. Their semi-synthetic derivatives include heroin, hydrocodone, oxycodone and buprenorphine. Opioids also include a range of synthetic or pharmaceutical opioids, such as methadone, pethidine, tramadol and fentanyl.119
"The group also comprises a diverse group of chemicals – opioid receptor agonists – that were initially developed by pharmaceutical companies with the aim of producing more effective opioids for pain management, but were later discarded or considered unsuitable for further development.120 Many of those substances, also known as research opioids, novel synthetic opioids or NPS opioids, are considered to be more potent than morphine; synthetic opioids that are analogues of fentanyl are considered to be 50–100 times more potent than morphine.121, 122, 123 Research or NPS opioids such as U-47700, AH-7921, fentanyl analogues (acrylfentanyl, butyrylfentanyl), the new class of benzimidazole (isotonitazene)124 and the more recent brorphine,125 to name but a few, have added to the ever-increasing complexity of opioids, both in terms of controlling the misuse of these substances and their public health implications. Many of the research opioids, such as U-47700 or butyrylfentanyl, have been put under international control in recent years, however. Moreover, some of the substances, such as W-15 and W-18, were initially introduced as potent opioids but were later found to have no activity on the opioid receptors, although they were put under national control in some countries.126 Nevertheless, research opioids are among the fastest increasing group among the wider new psychoactive substances identified or reported each year.127, 128"
United Nations Office on Drugs and Crime. World Drug Report 2021. Booklet Three: Drug Market Trends: Cannabis, Opioids. United Nations publication, Sales No. E.21.XI.8.