•It has been clinically observed that unanticipated conversions between opioids going beyond common metabolic pathways may occur, and these can be detected by high-quality assays [Haddox 2005]. For
example, patients prescribed only codeine might test positive for
codeine and morphine, and also hydrocodone and hydromorphone. Patients taking only morphine might also test positive for hydrocodone and/or hydromorphone.