An iontophoresis system includes a preloaded reservoir containing one or more doses of a therapeutic agent. As a result, the therapeutic agent does not have to be loaded into the reservoir prior to use. In such a system, the preloaded reservoir is generally disposable. Various components of the iontophoresis system can be combined with the reservoir in a disposable cartridge that is selectively connectable to other, reusable components of the iontophoresis system. In addition, the entire iontophoresis system can be formed from one or more disposable, one-time-use modules.