Long-term stability of morphine, codeine, and 6-acetylmorphine in real-life whole blood samples, stored at −20 °C

This study showed that in real life whole blood samples, the concentrations of morphine and codeine are relatively stable during long-term storage at −20 °C. 6-AM on the other hand, shows a considerable decrease in concentrations that is important to consider when interpreting results from reanalyses of forensic cases.