As far as I thought everything gets converted into codeine or morphine in the body. The only one's that go to codeine are, codeine & hydrocodone(vicodin), everything else gets converted to morphine(morphine, oxycodone, hydromorphone, herion, opium), but I also know fentanyl and methadone come up on a tox screen as different from the rest of the opiates so I'm not sure about those 2. Only the 15 panel tests for fentanyl it won't show up on the 12 panel. I'm so glad I got out when I did cause my "rock bottom" would have been ending up like this kid and that was probably not too far off. I love me some Fents but that is like dancing with death and I didn't give a fuck the past 3 years.