The citrate salt of fentanyl, a synthetic opioid related to the phenylpiperidines with analgesic and anesthetic properties. Fentanyl exerts its analgesic effect by selectively binding to the mu-opioid receptor in the central nervous system (CNS), thereby mimicking the effects of endogenous opiates. Additional pharmacological effects of fentanyl include anxiolysis, euphoria, feelings of relaxation, respiratory depression, constipation, miosis, and cough suppression. or A drug used to treat severe cancer pain that occurs even though the patient is already taking opioids. It is also used during anesthesia for surgery. Fentanyl citrate binds to opioid receptors in the central nervous system. It is a type of analgesic agent and a type of opioid.