Definition
7-hydroxymitragynine (abbreviated 7-OH-MG or 7-OH) is an indole alkaloid of kratom, structurally derived from mitragynine by hydroxylation at carbon C7. In the dry leaf it occurs in trace amounts - typically below 2 % of the total alkaloid content, corresponding to the order of tens to hundreds of milligrams per kilogram of raw powder.
Nevertheless, 7-OH-MG is described in the scientific literature as a pharmacologically significant component of kratom because of its high affinity for the μ-opioid receptor, many times greater than that of the parent mitragynine.
Relationship to mitragynine
7-OH-MG is formed by the oxidation of mitragynine - either enzymatically in the plant (the presence of cytochrome P450 in the leaves) or non-enzymatically during drying and storage of the raw material, especially on contact with atmospheric oxygen and UV radiation. In a fresh leaf the 7-OH-MG/mitragynine ratio tends to be lower than in older or improperly stored powder.
Structurally, the two compounds differ only in the presence of a hydroxyl group at carbon C7 of the indoline nucleus (C23H30N2O5, molar mass 414.5 g/mol). This small modification changes the molecule's conformation and its affinity for the target receptor.
A scientific view of potency
In vitro studies (Váradi et al. 2016) report that 7-OH-MG shows an affinity for the μ-opioid receptor of the order comparable to morphine and 10-17× higher than mitragynine. Functional assays (cAMP, [35S]GTPγS) show, as with mitragynine, partial agonism with a preference for the G-protein pathway over the β-arrestin pathway.
This description is purely scientific and serves to understand the pharmacological profile - none of the cited studies is a therapeutic recommendation.
Analytical detection
To determine 7-OH-MG in both plant material and biological matrices, the following are used as standard:
- HPLC-MS/MS (liquid chromatography with tandem mass detection) - the reference method in laboratories for determining the kratom alkaloid profile,
- UHPLC-DAD for screening,
- GC-MS after derivatisation (less common due to thermolability).
Typical limits of quantification (LOQ) are in the single-digit ng/ml range in plasma and single-digit μg/g in plant material. A validated method is described, for example, in Lu et al. (2009).
Frequently asked questions
Is 7-OH-MG formed during storage?
Yes. With access to oxygen and light, mitragynine is slowly oxidised to 7-OH-MG. For this reason, storage in opaque containers without access to air is recommended.
In what ratio to mitragynine is it usually present?
In a well-dried leaf, typically 0.1-2 % of the alkaloid profile, whereas mitragynine makes up 60-66 %. In terms of leaf weight, this is a few μg/g.
Why is it significant even in trace amounts?
Thanks to its order-of-magnitude higher affinity for the μ-opioid receptor, even a low concentration can contribute to the overall pharmacological profile of kratom. This is a recurring theme in scientific papers on kratom (Kruegel & Grundmann 2018).
Can 7-OH-MG be distinguished from mitragynine visually?
No. Both compounds are solid crystalline substances of similar colour. Reliable identification requires mass spectrometry or NMR.
References
- Takayama H. (2004). Chemistry and pharmacology of analgesic indole alkaloids from the Rubiaceous plant, Mitragyna speciosa. Chemical & Pharmaceutical Bulletin, 52(8), 916-928.
- Váradi A. et al. (2016). Mitragynine/Corynantheidine Pseudoindoxyls As Opioid Analgesics with Mu Agonism and Delta Antagonism, Which Do Not Recruit β-Arrestin-2. Journal of Medicinal Chemistry, 59(18), 8381-8397.
- Lu S. et al. (2009). Detection of mitragynine and its 9-hydroxy metabolite in human urine. Journal of Analytical Toxicology, 33(8), 418-422.
