Mitragynine, an indole alkaloid, is the most abundant active alkaloid in the plant Mitragyna speciosa, commonly known as Kratom and "Biak-Biak". Mitragynine demonstrates opioid-like activity of which has been attributed to the presence of the indole alkaloids, mitragynine and 7-hydroxymitragynine. Mitragynine itself acts primarily via μ-opioid receptors, though its oxidation product mitragynine pseudoindoxyl, acts as an even more potent and selective μ-opioid agonist with less affinity for δ or κ receptors. Another alkaloid with a major contribution to the μ-opioid activity of the kratom plant is the related compound 7-hydroxymitragynine, which while present in the plant in much smaller quantities than mitragynine, is a much more potent μ-opioid agonist. It is structurally related to both the yohimbe alkaloids and, more distantly, voacangine. Chemically, mitragynine is 9-methoxy-corynantheidine.
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