Fentanyl, also called N- (1-phenethyl-4-piperidyl) propionamide, a synthetic narcotic analgesic, is the most potent narcotic in clinical use (50 to 100 times more potent than morphine). The citrate salt, fentanyl citrate, is administered by injection, either intramuscularly or intravenously, sometimes in combination with a potent tranquilizer.

Fentanyl exerts its pain-relieving effects by acting on opioid receptors. Repeated activation of these receptors by narcotic drugs is suspected to play a role in drug addiction. In the second decade of the 21st century in the United States, fentanyl was one of the deadliest drugs of abuse.