The present invention provides novel methods for monitoring subject adherence in taking prescribed drugs by detecting markers in exhaled breath after a subject takes the prescribed drug. In particular, the present invention provides novel methods for making additives that are combined with the drug(s). Upon biological breakdown of the drug/additive formulation in a subject's body, markers resulting directly from the biological breakdown of the additives are detected in exhaled breath using sensor technology. In certain embodiments of the invention, the drug adherence monitoring systems and methods include a reporting system capable of tracking subject compliance (either remotely or proximately) and of providing necessary alerts to the subject, caregiver, healthcare provider, and the like.