Wikipedia
Acrylfentanyl
Acrylfentanyl (also known as acryloylfentanyl) is a highly potent opioid analgesic that is an analog of fentanyl and has been sold online as a designer drug. In animal studies the IC or half maximal inhibitory concentration for acrylfentanyl to displace naloxone is 1.4 nM, being slightly more potent than fentanyl itself (1.6 nM) as well as having a longer duration of action.