Fentanyl is perhaps the most well-known of the synthetic opioids, since it has been extensively researched and is approved for prescription use. It was discovered in the 1960’s and was only used for surgery, but its clinical use expanded in the 90’s when an extended release skin patch was developed as treatment for chronic pain.
Fentanyl patches used to treat pain
Fentanyl patches used to treat pain. (Photo by Nils Wommelsdorf, CC BY 2.0)

Fentanyl analogues have been designed to mimic fentanyl but have a slightly different chemical structure so they may have different effects. Following the discovery of fentanyl, some of its analogues were developed and brought to market for medical use. Recently many related compounds have been appearing on the illicit market that have no prior use in medicine. These new drugs fall into the category of novel psychoactive substances (NPS). Unfortunately, not much is known about the effects of numerous fentanyl analogues and more research is needed.