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Microbes, Metals, and Mitragynine in Commercial Kratom Products

Kratom is an herb derived from the leaves of the kratom tree (Mitragyna speciosa) indigenous to Southeast Asia. The leaves have traditionally been chewed as a stimulant to combat fatigue. In the United States in recent years, it has been sold as an “herbal supplement” with claims that it boosts mood and energy, and relieves pain.

Because it is classified as an herbal supplement, the Food and Drug Administration does not regulate the potency or purity of kratom. To explore the range of potency and impurities in commercially available kratom products, Prozialeck and colleagues legally purchased 8 different products from smoke shops in the western suburbs of Chicago and analyzed them using microbial culture techniques, mass spectrometry, and other techniques. Multiple species of bacteria were identified in 6 of the 8 products, but no Salmonella, in contrast with prior concerns over kratom contamination. The levels of mitragynine ranged from less than 4 mg/g to over 60 mg/g. Concerning amounts of toxic metals, including nickel and lead, were found in all but one product.

The presence of mitragynine in each sample indicates they are almost certainly from the kratom tree, the authors note, and natural products often contain multiple microbial species. The levels of heavy metals, especially lead, are the most concerning finding, they said, given that regular users may ingest 5 to 15 g of kratom per day.

“We have advocated for further research on the therapeutic potential of kratom,” the authors conclude, “and we stand by that position. However, we also find the present findings to be troubling. It is apparent that many of the kratom products being sold on the local level contain unknown levels of active agent (mitragynine) and are contaminated with metals, such as Pb and Ni, as well as microbes. This puts consumers at potential risk of adverse effects.”


1Prozialeck WC, Edwards JR, Lamar PC, et al. Evaluation of the mitragynine content, levels of toxic metals and the presence of microbes in kratom products purchased in the western suburbs of Chicago. Int J Environ Res Public Health. 2020;17(15):5512. doi:10.3390/ijerph17155512

Published date: Nov 20, 2020