4-chloroisobutyrylfentanyl 4-chloroisobutyrylfentanyl 4-chloroisobutyrylfentanyl (para-chloroisobutyrylfentanyl, 4-cl-ibf) is an opioid analgesic that is an analog of fentanyl, and has been sold online as a designer drug. 4-chloroisobutyrylfentanyllegal statuslegal status us: schedule i illegal in finland and sweden identifiers iupac name 2-methyl-n-(4-chlorophenyl)-n-propanamide cas number244195-34-4pubchem cid100974915unii6ds2gh6v2dchemical and physical dataformulac23h29cln2omolar mass384.95 g·mol−13d model (jsmol)interactive image smiles c3ccccc3ccn(cc1)ccc1n(c(=o)c(c)c)c(cc2)ccc2cl inchi inchi=inchi=1s/c23h29cln2o/c1-18(2)23(27)26(21-10-8-20(24)9-11-21)22-13-16-25(17-14-22)15-12-19-6-4-3-5-7-19/h3-11,18,22h,12-17h2,1-2h3key:ywhlygshoqkcjg-uhfffaoysa-n side effects 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. a new wave of fentanyl analogues and associated deaths began in around 2014 in the us, and have continued to grow in prevalence; especially since 2016 these drugs have been responsible for hundreds of overdose deaths every week. legal status para-chloroisobutyrylfentanyl has been a schedule i controlled drug in the united states since 1 february 2018. it was banned in finland in september 2017, and in sweden in october 2017.