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Molar mass368.496 g·mol−1
3D model (JSmol)

4-Fluoroisobutyrylfentanyl (also known as 4-FIBF and p-FIBF) is an opioid analgesic that is an analog of butyrfentanyl and structural isomer of 4-Fluorobutyrfentanyl and has been sold online as a designer drug.[1][2][3][4] It is closely related to 4-fluorofentanyl, which has an EC50 value of 4.2 nM for the human μ-opioid receptor.[5]

Side effects[edit]

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. 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.[6]


4-Fluoroisobutyrylfentanyl is a Schedule I controlled substance in the United States.[7] In the UK, it is a Class A drug. In Canada, it is a Schedule I drug.

See also[edit]


  1. ^ "FIBF". Cayman Chemical.
  2. ^ Watanabe, Shimpei; Vikingsson, Svante; Roman, Markus; Green, Henrik; Kronstrand, Robert; Wohlfarth, Ariane (July 2017). "In Vitro and In Vivo Metabolite Identification Studies for the New Synthetic Opioids Acetylfentanyl, Acrylfentanyl, Furanylfentanyl, and 4-Fluoro-Isobutyrylfentanyl". The AAPS Journal. 19 (4): 1102–1122. doi:10.1208/s12248-017-0070-z. PMID 28382544.
  3. ^ Helander, Anders; Bäckberg, Matilda; Signell, Patrick; Beck, Olof (3 July 2017). "Intoxications involving acrylfentanyl and other novel designer fentanyls – results from the Swedish STRIDA project". Clinical Toxicology. 55 (6): 589–599. doi:10.1080/15563650.2017.1303141. ISSN 1556-3650. PMID 28349714.
  4. ^ Strayer, Kraig E.; Antonides, Heather M.; Juhascik, Matthew P.; Daniulaityte, Raminta; Sizemore, Ioana E. (2018). "LC-MS/MS-Based Method for the Multiplex Detection of 24 Fentanyl Analogues and Metabolites in Whole Blood at Sub ng mL–1 Concentrations". ACS Omega. 3 (1): 514–523. doi:10.1021/acsomega.7b01536. ISSN 2470-1343. PMC 5793031. PMID 29399650.
  5. ^ Ulens, Chris; Boven, Maurits Van; Daenens, Paul; Tytgat, Jan (1 September 2000). "Interaction of p-Fluorofentanyl on Cloned Human Opioid Receptors and Exploration of the Role of Trp-318 and His-319 in μ-Opioid Receptor Selectivity". Journal of Pharmacology and Experimental Therapeutics. 294 (3): 1024–1033. ISSN 1521-0103. PMID 10945855.
  6. ^ Mounteney, Jane; Giraudon, Isabelle; Denissov, Gleb; Griffiths, Paul (July 2015). "Fentanyls: Are we missing the signs? Highly potent and on the rise in Europe". International Journal of Drug Policy. 26 (7): 626–631. doi:10.1016/j.drugpo.2015.04.003. PMID 25976511.
  7. ^ "Controlled Substances by DEA Drug Code Number" (PDF). Drug Enforcement Agency.