Various embodiments provide methods and systems for the biphasic iontophoretic transdermal delivery of therapeutic agents. An embodiment of a method for such delivery comprises positioning at least one electrode assembly in electrical communication with a patients skin. The assembly includes a solution comprising a therapeutic agent which passively diffuses into the skin. A dose of agent is delivered from the assembly into the skin during a first period using a first current having a characteristic e.g., polarity and magnitude, to repel the agent out of the assembly. During a second period, a second current having a characteristic to attract the agent is used to retain the agent in the assembly such that delivery of agent into skin is minimized. A dose of agent may be delivered on demand by an input from the patient. Embodiments may be used for delivery of agents which cause adverse effects from unwanted passive diffusion.
