Kratom's reputed pain-relief benefits could come from one of its metabolites

Currently, kratom is legal and available in the U.S. as a gray-market product, but it has an uncertain regulatory future. In the meantime, scientists are investigating the substance's physiological effects. Some prior research attributed these effects to mitragynine, the major active alkaloid in kratom, and its binding to an opioid receptor. However, 7-hydroxymitragynine (7-OH), another alkaloid present in the leaf at far lower concentrations, also interacts with that receptor. To clear up the matter, Jonathan A. Javitch, Susruta Majumdar, Dalibor Sames and colleagues set out to probe the pharmacological and metabolic mechanisms behind kratom's analgesic effects.

Through studies in cells and mice, the researchers showed that most of the analgesic effect is from 7-OH rather than mitragynine. They also found that metabolism of mitragynine in mouse and human liver preparations actually produces much more 7-OH than is present naturally in kratom. The team says that the results shed light on some of the seemingly contradictory reports on kratom, but more studies are still needed to see whether their findings in mice extend to humans.