Fentanyl is a synthetic, lipophilic phenylpiperidine opioid agonist with analgesic and anesthetic properties. Fentanyl selectively binds to and activates the mu-receptor in the central nervous system (CNS) thereby mimicking the effects of endogenous opiates. Activation of the mu-subtype opioid receptor stimulates the exchange of GTP for GDP on the G-protein complex and subsequently inhibits adenylate cyclase. This causes a decrease in intracellular cAMP which inhibits cAMP-mediated calcium influx into the cell via the calcium channels and thereby results in hyperpolarization and reduced neuronal excitability.