isofentanyl isofentanyl isofentanyl (3-methyl-benzylfentanyl) is an opioid analgesic that is an analog (and structural isomer) of fentanyl first invented in 1973, and which has been sold as a designer drug. isofentanyllegal statuslegal status us: schedule i identifiers iupac name n-(1-benzyl-3-methylpiperidin-4-yl)-n-phenylpropanamide cas number79278-40-3 ypubchem cid10449690chemspider8625107uniibt57arh9qxcomptox dashboard (epa)dtxsid00747120 chemical and physical dataformulac22h28n2omolar mass336.479 g·mol−13d model (jsmol)interactive image smiles c2ccccc2n(c(=o)cc)c1ccn(cc1c)cc3ccccc3 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 as a structural isomer of fentanyl itself, isofentanyl is banned under drug analogue laws in many jurisdictions around the world. in the united states, fentanyl-related substances are schedule i controlled substances.