Determination of mitragynine concentrations in medicolegal death investigations at the Oklahoma Office of the Chief Medical Examiner from 2022 to 2023

The prevalence of mitragynine, the major psychoactive component in kratom, has increased in forensic toxicology casework due to its current legal status and ease of accessibility in local shops and the online community. This study presents 28 death investigation cases from 2022 to 2023 in Oklahoma including mitragynine concentrations alongside case demographics, pathological findings, and additional toxicological results. Quantitative results for mitragynine in heart blood, femoral blood, and liver were obtained by liquid chromatography/tandem mass spectrometry (LC/MS–MS) following supported liquid extraction. Postmortem heart blood concentrations ranged from 130 to 2600 ng/mL with a mean of 735 ng/mL and a median of 550 ng/mL. Postmortem femoral blood concentration ranged from 130 to 7500 ng/mL with a mean of 900 ng/mL and a median of 570 ng/mL. Postmortem redistribution ratios were determined for 25 cases that had paired central and peripheral samples (range 0.31–1.86) and for 20 cases that had paired peripheral and liver samples (range 0.86–9.70). Overall central to peripheral and liver to peripheral ratios suggest mitragynine exhibits minimal postmortem redistribution, although a few individual cases demonstrated variability. Twenty‐two cases listed mitragynine in the cause of death with 21 of those cases including at least one other drug detected and reported on the death certificate. The data presented shows the importance of quantifying mitragynine in medicolegal death investigations to aid in cause and manner of death determination.