The IONSYS transdermal system is composed of an electronic controller connected to a drug unit with two hydrogels. The controller has a digital display, a light window, and a recessed dose activation button. Each IONSYS system contains 9.7 mg of fentanyl and delivers 40 micrograms per dose, to a maximum of 80 doses (3.2 mg/24 hours). The maximum treatment duration is 72 hours, although the majority of patients should only need one system.