benzylfentanyl benzylfentanyl benzylfentanyl (r-4129) is a fentanyl analog. it was temporarily placed in the us schedule i by emergency scheduling in 1985 due to concerns about its potential for abuse as a designer drug, but this placement was allowed to expire and benzylfentanyl was formally removed from controlled substance listing in 2010, after the dea's testing determined it to be "essentially inactive" as an opioid. benzylfentanyl has a ki of 213 nm at the mu opioid receptor, binding around 1/200 as strong as fentanyl itself, though it is still slightly more potent than codeine. not to be confused with benzoylfentanyl. benzylfentanyl names preferred iupac name n-(1-benzylpiperidin-4-yl)-n-phenylpropanamide identifiers cas number 1474-02-8 y 3d model (jsmol) interactive image chemspider 220920 echa infocard 100.014.559 pubchem cid 252141 unii 9bv2d1a57h y comptox dashboard (epa) dtxsid00163705 inchi inchi=1s/c21h26n2o/c1-2-21(24)23(19-11-7-4-8-12-19)20-13-15-22(16-14-20)17-18-9-5-3-6-10-18/h3-12,20h,2,13-17h2,1h3key: poqdxifvwvzvml-uhfffaoysa-n smiles ccc(=o)n(c1ccn(cc1)cc2=cc=cc=c2)c3=cc=cc=c3 properties chemical formula c21h26n2o molar mass 322.452 g·mol−1 except where otherwise noted, data are given for materials in their standard state (at 25 °c , 100 kpa). infobox references 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. legal status benzylfentanyl is a list i chemical in the u.s.. benzylfentanyl is illegal in germany (anlage i)