Furanylfentanyl (Fu-F) is an opioid analgesic that is an analog of fentanyl[1] and has been sold as a designer drug.

Fentanyl analogs have killed hundreds of people throughout Europe and the former Soviet republics since the most recent resurgence in use began in Estonia in the early 2000s, and novel derivatives continue to appear.

[9][10][11] Furanylfentanyl may be measured in blood or urine to monitor for use, confirm a diagnosis of poisoning, or assist in a medicolegal death investigation.

Commercially available immunoassays are often used as initial screening tests, but chromatographic techniques are generally used for confirmation and quantitation.

[15] The United States Drug Enforcement Administration (DEA) proposed a temporary placement of furanylfentanyl into Schedule I of the Controlled Substances Act on 27 September 2016.