Chemistry and Pharmacology: Fentanyl is about 100 times more potent than morphine as an analgesic. It is a µ-opioid receptor agonist with high lipid solubility and a rapid onset and short duration of effects. Fentanyl rapidly crosses the blood-brain barrier. It is similar to other -µopioid receptor agonists (like morphine or oxycodone) in its pharmacological effects and produces analgesia, sedation, respiratory depression, nausea, and vomiting. Fentanyl appears to produce muscle rigidity with greater frequency than other opioids.