-(1-phenethyl-4-piperidyl)propionanilide, synthetic narcotic analgesic drug, 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 tranquillizer. The duration of its pain-relieving action is short.