Synthetic opioids refer to a category of novel psychoactive substances (NPS) that are either known to be opiates or have opiate-like effects. These are not naturally occurring substances, although they have effects related to the naturally occurring drugs from several species of the opium poppy plant. These plants have been cultivated and used by humans for medicinal and recreational purposes over thousands of years, from which well-known opiates like morphine and heroin are derived.

Fentanyl

Fentanyl is perhaps the most well-known of the synthetic opioids, since it has been extensively researched and is one of the only substances approved for prescription use. Discovered in the 1960’s, fentanyl 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)

Following the discovery of fentanyl, some of its analogues were developed and brought to market for medical use. But recently many related compounds have been appearing on the illicit market that have no prior use in medicine. 

Unfortunately, not much is known about the effects of numerous fentanyl analogues like acetyl, butyl, or furanyl fentanyl, and other opiate-like NPS that have begun to appear. Currently, synthetic opioids are being produced in clandestine labs and are often used as cutting agents to heroin or other drugs. Many of these substances are known only by their chemical shorthand, such as W-18, U-47700 and AH-7921. Potency and effects can vary widely among these substances, and short and long term health risks are not always clearly known.