Fentanyl is an opioid analgesic with pharmacological effects similar to morphine. Fentanyl interacts predominately with the opioid µ-receptor. In clinical settings, fentanyl exerts its principal pharmacologic effects on the central nervous system. The fentanyl citrate oral transmucosal troche, Actiq (Cephalon, Inc.), is indicated only for the management of breakthrough cancer pain in patients with malignancies who are already receiving and who are tolerant to prior therapy for their underlying persistent cancer pain.