Fentanyl skin patch is used to treat severe pain, including acute pain following surgery. Ionsys® is applied by your healthcare provider in a hospital setting after surgery for the short-term management of acute pain. Duragesic® is used for pain severe enough to require around-the-clock pain relief for a long period of time. Fentanyl is a strong narcotic analgesic (pain medicine). It acts on the central nervous system (CNS) to relieve pain.