4-methoxybutyrfentanyl 4-methoxybutyrfentanyl 4-methoxybutyrfentanyl (also known as 4-meo-bf) is an opioid analgesic that is an analog of butyrfentanyl and has been sold online as a designer drug. 4-methoxybutyrfentanylclinical dataother namespara-methoxybutyryl fentanyllegal statuslegal status ca: schedule i de: npsg (industrial and scientific use only) uk: class a us: schedule i illegal in sweden identifiers iupac name n-(4-methoxyphenyl)-n--butanamide cas number2088842-68-4pubchem cid118796493chemspider52085457uniiy72z69r7k3chemical and physical dataformulac24h32n2o2molar mass380.532 g·mol−13d model (jsmol)interactive image smiles cccc(=o)n(c1ccn(cc1)ccc2ccccc2)c3ccc(oc)cc3 inchi inchi=1s/c24h32n2o2/c1-3-7-24(27)26(21-10-12-23(28-2)13-11-21)22-15-18-25(19-16-22)17-14-20-8-5-4-6-9-20/h4-6,8-13,22h,3,7,14-19h2,1-2h3key:fnvseqcpmxwqkg-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. life-threatening adverse reactions have been observed. legal status 4-methoxybutyrfentanyl is illegal in sweden as of 26. january 2016. 4-methoxybutyrfentanyl is a schedule i controlled drug in the usa since 1. february 2018.