A sublingual preparation of a short-acting, synthetic anilidopiperidine opioid with analgesic activity. After rapid sublingual transmucosal absorption, the active ingredient fentanyl selectively binds to and activates mu-opioid receptors in the central nervous system (CNS), mimicking the effects of endogenous opiates. or A form of the drug fentanyl that is sprayed under the tongue and then absorbed into the blood. It is being studied in the treatment of breakthrough pain (pain that occurs even when pain-control medication is already being used) in cancer patients. Fentanyl is a type of opioid analgesic.