The Science of Kratom
Independent, sourced, plain-language.
What the research actually says.
Last updated: March 2026 · All claims sourced from peer-reviewed literature
Alkaloid Encyclopedia
Plain-language profiles of every major compound in kratom. What each one does, at what dose, and what it means for you.
ExploreDrug Interaction Checker
Know before you combine. 0 documented interactions with medications, supplements, and substances — severity rated and sourced.
ExploreLiterature Database
98 peer-reviewed papers on kratom pharmacology, toxicology, and clinical observations. Searchable, filterable, with plain-language summaries.
ExploreTaper & Dosage Research
What the research says about dependence, withdrawal timelines, and reduction approaches.
ExploreHarm Reduction Guide
Evidence-based safer use information including how to read a COA, understand your product, and recognize adverse effects.
ExploreAdvanced: Receptor Binding Data
Compound library & affinity table from the original Pharmacological Dossier
Compound Library
7-Hydroxymitragynine
Mechanism of Action
Partial agonist at mu-opioid receptors (MOR). Exhibits ~13x higher potency than morphine in antinociceptive assays. Metabolically derived from mitragynine via hepatic CYP3A4 oxidation.
Receptor Binding Summary
High MOR affinity (Ki ~7.8 nM). Moderate delta-opioid receptor (DOR) affinity. Low kappa-opioid receptor (KOR) interaction.
Biased Agonism Note
Demonstrates significant G-protein bias over beta-arrestin-2 recruitment. This profile is associated with reduced respiratory depression and constipation liability relative to classical opioids.
Mitragynine Pseudoindoxyl
Mechanism of Action
Rearrangement product of 7-hydroxymitragynine. MOR agonist with potency comparable to 7-OH. Does not recruit beta-arrestin-2 at analgesic doses in rodent models.
Receptor Binding Summary
High MOR affinity (Ki ~5.1 nM). DOR antagonist activity. Minimal KOR engagement.
Biased Agonism Note
Among the most G-protein-biased opioid agonists identified. Beta-arrestin-2 recruitment is near-zero at therapeutic concentrations, yielding a favorable side-effect profile in preclinical models.
MGM-15
Mechanism of Action
Synthetic analog of mitragynine. Designed to enhance G-protein signaling while maintaining low beta-arrestin recruitment. MOR partial agonist.
Receptor Binding Summary
Moderate MOR affinity (Ki ~35 nM). Low DOR affinity. Negligible KOR activity.
Biased Agonism Note
Engineered for maximal G-protein bias. Preclinical data shows antinociception without significant respiratory depression at equianalgesic doses.
MGM-16
Mechanism of Action
Structural isomer of MGM-15. Enhanced metabolic stability. MOR partial agonist with extended duration of action in rodent models.
Receptor Binding Summary
High MOR affinity (Ki ~12 nM). Moderate DOR affinity (Ki ~180 nM). Low KOR affinity.
Biased Agonism Note
Strong G-protein bias. Beta-arrestin-2 recruitment is moderate at supratherapeutic concentrations but minimal at analgesic doses. Ceiling effect observed at higher doses.
SR-17018
Mechanism of Action
Non-indole-based MOR agonist. Structurally distinct from mitragynine-class compounds. Designed as a tool compound to study G-protein-biased signaling.
Receptor Binding Summary
High MOR affinity (Ki ~8.5 nM). Low DOR affinity. Very low KOR affinity.
Biased Agonism Note
One of the most biased MOR agonists in published literature (>100x G-protein preference over beta-arrestin). However, some studies suggest bias may be assay-dependent.
Receptor Affinity Table
Binding affinity values (Ki, nM) from published radioligand displacement assays. Lower Ki = higher affinity. G-protein bias score represents log(tau/KA) differential between G-protein and beta-arrestin-2 pathways. "ant." = antagonist activity at that receptor.
| Compound | Mu-Opioid (MOR) | Delta-Opioid (DOR) | Kappa-Opioid (KOR) | Signaling Bias | ||||
|---|---|---|---|---|---|---|---|---|
| Ki (nM) | Profile | Ki (nM) | Profile | Ki (nM) | Profile | Beta-Arr. | G-Bias | |
| 7-Hydroxymitragynine | 7.8 | moderate | 156 | favorable | >1000 | favorable | low | 3.2 |
| Mitragynine Pseudoindoxyl | 5.1 | moderate | 82 (ant.) | favorable | >1000 | favorable | low | 4.8 |
| MGM-15 | 35 | favorable | >500 | favorable | >1000 | favorable | low | 3.5 |
| MGM-16 | 12 | moderate | 180 | favorable | >500 | favorable | moderate | 2.8 |
| SR-17018 | 8.5 | moderate | >500 | favorable | >1000 | favorable | low | 5.1 |