Butyrfentanyl or butyrylfentanyl is a potent short-acting synthetic opioid analgesic drug. It is an analog of fentanyl with around one quarter of its potency.
Butyrfentanyl has no current legitimate clinical applications; however, it is being sold as designer drug.
As of May 2016, butyrfentanyl is a Schedule I controlled substance in the United States.