World Health Organization 2017:
4-Fluoroisobutyrfentanyl belongs to the 4-anilidopiperidine class of synthetic opioids which is the same class of opioids as internationally controlled fentanyl and its derivatives. 4-fluoroisobutyrfentanyl is one of the latest fentanyl derivatives to be sold and used in a similar manner as other licit and illicit opioids. 4-Fluoroisobutyrfentanyl can be found in trace amounts in illicitly manufactured material or mixed with heroin or other opioids making the detection very challenging for forensic laboratories and likely lead to the under reporting of the extent to which it appears on the market. Because abusers of 4-fluoroisobutyrfentanylare likely to obtain these substances through unregulated sources and in uncontrolled clandestine laboratories, the identity, purity, and quantity are uncertain and inconsistent, thus posing significant adverse health risks to the end user.

World Health Organization 4-FIBF (PDF 21 pages):
https://www.who.int/medicines/access/controlled-substances/CriticalReview_4FIBF.pdf

EMCDDA - Europol Joint Report 2017:

• 4-Fluoroisobutyrylfentanyl has been available in the European Union since at least July 2016.
• 4-Fluoroisobutyrylfentanyl is sold and used a substitute for illicit opioids and prescription opioids.
• Serious concerns exist that the substance could be supplied surreptitiously to a range of drug users.

European Monitoring Centre for Drugs and Drug Addtiction Joint Report (PDF 14 pages): http://www.emcdda.europa.eu/system/files/publications/5482/2017.4967_TDAS17007ENN_PDFWEB.pdf

4-Fluoroisobutyrfentanyl:

• An opioid analgesic
• An analog of butyrfentanyl
• Has been sold online as a designer drug
• Analgesic potency is almost ten times of that reported for morphine
• Side effects of fentanyl analogs are similar to those of fentanyl itself, which include itching, nausea and potentially serious respiratory depression, which can be life-threatening.