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Mitragynine Pseudoindoxyl

MPI · CAS n/a

Pseudoindoxyl alkaloid

Formula

C₂₃H₂₈N₂O₅

Molecular Weight

412.48 g/mol

Abundance in Leaf

Not found in leaf

Last Reviewed

2026-03-12

What Is Mitragynine Pseudoindoxyl?

Mitragynine pseudoindoxyl (MPI) is a rearrangement product of 7-hydroxymitragynine, formed during chemical processing or metabolic conversion — it is not naturally present in kratom leaf. MPI is a potent mu-opioid receptor agonist with affinity comparable to 7-OH (Ki ~5.1 nM). Its most notable feature is near-zero beta-arrestin-2 recruitment at analgesic doses, making it one of the most G-protein-biased opioid agonists identified. In preclinical models it produces analgesia with minimal respiratory depression and constipation. MPI is a research compound and is not found in consumer kratom products.

Dose-Dependent Effects

Receptor Activity

Receptor	Ki (nM)	Activity Type	What This Means
Mu-opioid (MOR)	~5.1	Full agonist (G-protein biased)	Potent activation of pain-relief receptors with near-zero beta-arrestin recruitment, suggesting reduced respiratory depression liability.
Delta-opioid (DOR)	—	Antagonist	Blocks delta-opioid receptors, a profile shared with several other mitragynine-class compounds.

Safety & Adverse Effects

Research status

MPI is a research-only compound. All data comes from preclinical (in vitro and animal) studies. It is not present in commercial kratom products.

Source: Váradi et al. 2016

Drug Interactions

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COA Connection

Appears on Certificates of Analysis as: N/A. Graded under Not measured on COAs (Research compound).

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Cited Literature

[1]

Váradi A, Marrone GF, Palmer TC, et al. (2016). Mitragynine/corynantheidine pseudoindoxyls as opioid analgesics with mu agonism and delta antagonism, which do not recruit β-arrestin-2. J Am Chem Soc.

DOI: 10.1021/jacs.6b00360

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