Devices, systems and methods for controlling the application of current and/or voltage to deliver drug from patient contacts of an electrotransport drug delivery device by indirectly controlling and/or monitoring the applied current without directly measuring from the cathode of the patient terminal. In particular, described herein are electrotransport drug delivery systems including constant current delivery systems having a feedback current and/or voltage control module that is isolated from the patient contacts (e.g., anodes and cathodes). The feedback module may be isolated by a transistor from the patient contacts; feedback current and/or voltage control measurements may be performed at the transistor rather than at the patient contact (e.g., cathode).