Case-control study of mitragynine deaths in Florida.

Kratom use has increased in the USA, with its primary alkaloid, mitragynine, detected in postmortem toxicology, and implicated in reported fatalities. This study evaluated toxicologic concentrations and autopsy findings associated with deaths attributed to mitragynine. Autopsy and postmortem toxicology reports were obtained from the majority of Florida medical examiner districts over 5 years for decedents in whom mitragynine was listed as a cause of death (mitragynine-induced fatalities). A comparison group included cases from a single county in which mitragynine was detected but not deemed causal (mitragynine-associated deaths). Demographic, toxicologic, and autopsy data were abstracted using standardized instruments. Thirty-eight mitragynine-induced fatalities and 111 mitragynine-associated deaths were identified, with similar demographic characteristics between groups. Mitragynine-associated deaths all featured co-exposures, including fentanyl (n = 84), cocaine (n = 49), and ethanol (n = 29). Mitragynine-induced fatalities had no toxic levels of any other substance and demonstrated higher rates of pulmonary edema (55.6% vs 31.5%), hepatomegaly (47.4% vs 14.4%), minor facial trauma (18.4% vs 5.4%), and cardiomegaly (47.4% vs 11.8%). Mean blood mitragynine concentrations were substantially higher in mitragynine-induced fatalities (2486 µg/L; 95% CI 1607-2863) compared with mitragynine-associated deaths (179 µg/L; 95% CI 217-375), suggesting a concentration-dependent association with fatal toxicity. Mitragynine toxicity accounts for a notable number of deaths.