A system for administering a therapeutic agent to a subject; for administering a first pharmaceutically-acceptable taggant to the subject at least substantially concurrent with the therapeutic agent, the first pharmaceutically-acceptable taggant having a pharmacokinetic profile; and for administering a second pharmaceutically-acceptable taggant to the subject with the first pharmaceutically-acceptable taggant, the second pharmaceutically-acceptable taggant having a pharmacokinetic profile different from the pharmacokinetic profile of the first pharmaceutically-acceptable taggant.