From kratom to 7-hydroxymitragynine: evolution of a natural remedy into a public-health threat

Kratom (Mitragyna speciosa), native to Southeast Asia, has traditionally been consumed as fresh leaves or teas. Under those conditions, exposure to 7-hydroxymitragynine (7-OH)-a potent μ-opioid receptor agonist-is minimal, as it occurs only at trace levels in leaf material. By contrast, the U.S. market offers chemically enriched or semi-synthetic 7-OH products, often marketed as 'kratom' yet chemically distinct from botanical preparations.

'7-OH', '7-hydroxymitragynine', and 'kratom' were used as keywords; relevant literature was obtained from PubMed, Web of Science, and Google Scholar.

Pharmacological studies consistently identify 7-OH as a partial μ-opioid receptor agonist with nanomolar affinity, greater efficacy than mitragynine, and often exceeding the potency of morphine. Animal experiments demonstrate robust antinociceptive effects, respiratory depression, tolerance, dependence, and reinforcing properties characteristic of opioids. Human pharmacokinetic studies show systemic exposure after kratom ingestion, but concentrated 7-OH products bypass metabolic formation, producing markedly higher exposures. Regulatory surveillance, poison-center data, and marketplace audits confirm a rapid increase in availability and use of these products. State health departments have reported severe intoxications and fatalities. Clinical cases describe escalating use, medically managed withdrawal, and psychiatric destabilization, while forensic investigations document postmortem concentrations consistent with fatal opioid toxicity. Pediatric risk is amplified by developmental susceptibility, absence of age restrictions, and marketing in confectionary formats. Emerging analogues such as MGM-15 further extend this trajectory.

Collectively, the evidence demonstrates that concentrated 7-OH products are pharmacologically and toxicologically distinct from kratom leaf and pose significant risks of morbidity and mortality under typical conditions of use.