Parafluorofentanyl (4-Fluorofentanyl) is an opioid analgesic being an analogue of fentanyl developed by Janssen Pharmaceutica in the 1960s.
4-Fluorofentanyl was sold briefly on the US black market in the early 1980s, before the introduction of the Federal Analog Act which for the first time attempted to control entire families of drugs based on their structural similarity rather than scheduling each drug individually as they appeared.
In 2021, Para-fluorofentanyl and carfentanil have been linked to several deaths in Louisiana.
Para-fluorofentanyl is a scheduled I substance in the United States.