Fentanyl citrate is an opioid pain medication. An opioid is sometimes called a narcotic. Fentanyl citrate treats "breakthrough" cancer pain that is not controlled by other medicines. This medication is not for treating pain that is not cancer-related, such as migraine headaches or pain after surgery. Fentanyl citrate is available only from a certified pharmacy under a special program called Actiq REMS Program. Fentanyl citrate may also be used for purposes not listed in this medication guide.