Medically reviewed
Reviewed for clinical accuracy by Brian Trappler, MD — Board-Certified Psychiatrist (ABPN), Associate Professor in Clinical Psychiatry (retired), SUNY Downstate Medical Center. Last reviewed: May 3, 2026.
Kratom is routinely marketed — and discussed — as if it were a single-compound product. In practice, Mitragyna speciosa leaf contains over 40 naturally occurring alkaloids with distinct receptor targets, varying abundances, and partially overlapping pharmacological activities.[1] Understanding the full alkaloid picture matters for two practical reasons: it explains why kratom’s effects are not fully predictable from mitragynine percentage alone, and it clarifies the safety considerations that any informed user should know.
What are alkaloids and why does kratom contain them?
Alkaloids are nitrogen-containing organic compounds produced by plants as secondary metabolites — they serve defensive, competitive, or ecological functions in the plant’s natural environment. Caffeine in coffee, morphine in opium poppies, quinine in cinchona bark, and nicotine in tobacco are all alkaloids.
Kratom’s alkaloids are concentrated in the leaf and belong primarily to the indole alkaloid family — specifically the monoterpenoid indole alkaloid class, which is also found in medically significant plants across the Rubiaceae and Apocynaceae families.[2] The two most studied kratom alkaloids, mitragynine and 7-hydroxymitragynine, interact with opioid receptors and adrenergic receptors, giving kratom its characteristic dose-dependent pharmacological profile.[1]
For broader botanical context, see: What Is Kratom?
What is mitragynine and how does it work?
Mitragynine (chemical formula C₂₃H₃₀N₂O₄) is the most abundant alkaloid in kratom leaf, typically comprising 60–70% of the total alkaloid content across commercial products, though this figure varies with strain and processing.[1]
Mitragynine is a partial agonist at mu-opioid receptors (MOR), the same receptor class targeted by morphine and codeine — though with important pharmacological differences.[4] Research by Kruegel et al. demonstrated that mitragynine shows “biased agonism” — it activates the G-protein signaling pathway but recruits beta-arrestin-2 less than classical opioids, a profile associated with potentially reduced respiratory depression risk compared to full mu-opioid agonists.[1] Mitragynine also interacts with delta-opioid receptors, adrenergic receptors, and serotonin receptors, contributing to its stimulant effects at lower doses.[4] Obeng et al. (2022) in the Journal of Pharmacology and Experimental Therapeutics evaluated this mu-opioid and alpha-2 adrenergic dual activity head-to-head in rats and showed that mitragynine and 7-HMG produce distinct interactive profiles across these two receptor systems — the pharmacological substrate for why low-dose kratom reads as stimulant and high-dose kratom reads as opioid-like in user reports.[10]
Mitragynine undergoes hepatic metabolism primarily via CYP3A4, with a plasma half-life of approximately 9 hours in humans.[5] This metabolism pathway matters clinically: CYP3A4 is responsible for metabolizing many prescription medications, and mitragynine inhibits this enzyme, creating meaningful drug interaction potential.[6]
Key pharmacological facts about mitragynine:
- Partial MOR agonist with biased agonism profile (reduced beta-arrestin-2 recruitment)[1]
- Also active at delta-opioid, alpha-2 adrenergic, and 5-HT₂A receptors[4]
- Metabolized in vivo to 7-hydroxymitragynine by hepatic CYP3A4[3]
- Plasma half-life ~9 hours; primarily hepatic clearance[5]
- CYP3A4 and CYP2D6 inhibitor — drug interaction risk with co-administered medications[6]
What is 7-hydroxymitragynine?
7-Hydroxymitragynine (7-HMG) is an oxygenated metabolite of mitragynine present naturally in kratom leaf at under 2% of total alkaloids — but it is pharmacologically important far beyond its abundance.[3]
Kruegel et al. (2019) demonstrated that 7-HMG is generated in vivo by hepatic CYP3A4 metabolism of mitragynine, and may be a primary mediator of kratom’s analgesic effects.[3] In animal models, 7-HMG showed approximately 13 times greater potency than morphine at mu-opioid receptors and crossed the blood-brain barrier more readily than the parent compound mitragynine.[1]
This prodrug relationship — mitragynine partially converting to the more potent 7-HMG in the liver — has practical implications:
- Individual variability in CYP3A4 activity (genetics, other drugs, liver function) affects how much 7-HMG a person generates
- Products deliberately enriched with 7-HMG (documented in adulteration cases) are meaningfully more potent and carry higher dependence risk[1]
- 7-HMG levels on a COA far above the natural threshold (~0.02%) are a flag for potential adulteration
For a detailed MG vs. 7-HMG comparison including potency modeling, see: Kratom Alkaloids Explained: MG vs. 7-HMG Deep Dive
What do the minor kratom alkaloids do?
Beyond mitragynine and 7-HMG, kratom leaf contains approximately 40 additional alkaloids at concentrations typically below 1% each.[1] Most have limited published human research, but their receptor activity has been partially characterized:
Speciociliatine (~1% of total alkaloids) is a diastereomer of mitragynine with weaker mu-opioid receptor activity. Research suggests it may modulate GI motility via peripheral opioid receptors, contributing to kratom’s constipation effect at higher doses.[2] Kamble et al. (2022) in the AAPS Journal specifically profiled speciociliatine’s metabolism — characterizing phase-I and phase-II pathways and confirming that it is not a pharmacologically inert minor compound, as often assumed, but a legitimate metabolic and pharmacological participant in kratom exposure.[9]
Paynantheine is a smooth muscle relaxant with adrenergic receptor activity. Its precise role in kratom’s pharmacological profile in humans is not well-defined, but it may contribute to muscle relaxation reported at moderate doses.[2]
Speciogynine is structurally related to speciociliatine with comparable weak opioid receptor activity. It may contribute to peripheral effects without significant CNS activity.[2]
Corynantheidine is notable for demonstrating antagonist activity at opioid receptors in some laboratory studies — raising the possibility that minor alkaloids may modulate or partially counteract the agonist activity of mitragynine and 7-HMG. This may be one reason kratom’s subjective profile differs from classical opioids at equivalent receptor occupancy[7].[1]
Mitraphylline is an oxindole alkaloid that also appears in cat’s claw (Uncaria tomentosa). It has demonstrated immunomodulatory and vasodilatory activity in laboratory studies; its contribution to kratom pharmacology in humans is not established.
Rhynchophylline is notable for NMDA receptor antagonist activity in vitro — a mechanism distinct from any other kratom alkaloid — and anti-arrhythmic effects in animal models. Its pharmacological contribution at the trace concentrations found in kratom is unclear.[2]
The practical consequence of this minor alkaloid complexity: two kratom products with identical mitragynine percentages may produce meaningfully different subjective experiences, because the full alkaloid profile — not just mitragynine content — shapes the overall pharmacological picture.
Full kratom alkaloid reference table
Key Kratom Alkaloids: Abundance, Receptor Targets, and Notes
| Alkaloid | Typical Abundance | Primary Receptor Target(s) | Key Notes |
|---|---|---|---|
| Mitragynine | 60–70% | MOR partial agonist; alpha-2 adrenergic; 5-HT₂A; delta-opioid | Biased agonism; prodrug for 7-HMG via CYP3A4 |
| 7-Hydroxymitragynine | <2% naturally | Full MOR agonist (~13× morphine potency in animal models) | Key analgesic mediator; generated in vivo from MG |
| Speciociliatine | ~1% | Weak MOR agonist; peripheral GI opioid receptors | May contribute to constipation; diastereomer of MG |
| Paynantheine | <1% | Smooth muscle relaxant; possible adrenergic activity | May contribute to muscle relaxation effects |
| Speciogynine | <1% | Weak opioid receptor activity | Related to speciociliatine; primarily peripheral |
| Corynantheidine | <1% | Opioid receptor antagonist (some models) | May modulate or counteract MG/7-HMG agonism |
| Mitraphylline | <1% | Immunomodulatory; vasodilatory | Oxindole alkaloid; also in cat’s claw |
| Rhynchophylline | Trace | NMDA receptor antagonist; anti-arrhythmic (in vitro) | Only kratom alkaloid with known NMDA activity |
Sources: Kruegel & Grundmann 2018[1]; Hanapi et al. 2021[2]; Kruegel et al. 2019[3]. Abundance figures are typical ranges from HPLC analyses; individual products vary.
How do kratom alkaloids interact with drug-metabolizing enzymes?
One of the most clinically relevant findings in kratom alkaloid research is the inhibition of cytochrome P450 (CYP) enzymes — the liver’s primary drug-metabolizing enzyme system. Kong et al. (2011) demonstrated that kratom alkaloid extract significantly inhibited CYP3A4, CYP2D6, and CYP1A2 in high-throughput fluorometric assays.[6] Hanapi et al. (2021) subsequently identified that mitragynine and related alkaloids interact directly with CYP3A4, CYP2D6, CYP2C9, and CYP1A2.[2]
CYP enzyme inhibition by kratom alkaloids may reduce clearance of co-administered drugs, elevating plasma concentrations and potentially amplifying their effects or toxicity. Drug classes metabolized via these pathways include:
- CYP3A4: Benzodiazepines, many SSRIs, statins, macrolide antibiotics, immunosuppressants
- CYP2D6: Opioid analgesics (codeine, tramadol, oxycodone), many antidepressants, beta-blockers
- CYP1A2: Caffeine, theophylline, clozapine, certain antidepressants
This is one of the primary reasons users on prescription medications should disclose kratom use to their prescribing physician before combining it with any prescription drug.[2] For the full safety and drug interaction overview, see: Kratom Side Effects Guide
Why do alkaloid profiles vary between products?
Kratom alkaloid content is not a fixed property of the plant species — it varies substantially based on multiple factors.[1] This variability explains batch-to-batch inconsistency even within the same vendor and product line:
- Harvest maturity. Leaf alkaloid content changes as the leaf matures. Vein color (white → green → red) partially reflects this — mature red-vein leaves typically have higher alkaloid density and a different mitragynine-to-minor-alkaloid ratio than young white-vein leaves. Published HPLC analyses show notable variation across strain categories.
- Drying and processing method. Sun-drying, indoor fermentation, and blending all affect the final alkaloid profile. Alkaloids degrade under UV exposure; fermentation may increase certain oxidized alkaloid forms.[1]
- Growing conditions. Soil mineral content, humidity, rainfall patterns, and tree genetics all contribute to alkaloid yield variability across Indonesian growing regions (Kalimantan, Sumatra, Sulawesi).
- Blending. Many commercial products blend material from multiple sources, averaging out regional variation. This can improve consistency but obscures strain-specific alkaloid data.
This variability is exactly why batch-specific COA data matters. A lab report for a specific lot is the only reliable way to know the actual alkaloid content of a specific product.
How do you read alkaloid content on a kratom lab report?
Reputable vendors publish a Certificate of Analysis (COA) for each batch, generated by an accredited independent laboratory. Alkaloid content on a COA is typically reported in two formats — percentage by weight, and milligrams per gram:
How to Interpret Kratom COA Alkaloid Data
| COA Field | What It Means | Typical Range (Quality Powder) |
|---|---|---|
| Mitragynine % | Mitragynine as % of total powder weight | 1.2–1.8% |
| Mitragynine mg/g | Milligrams of mitragynine per gram of powder | 12–18 mg/g |
| 7-HMG % | 7-Hydroxymitragynine as % of powder weight | <0.02% (flag if significantly higher) |
| Total Alkaloids % | Combined measurable alkaloid content | 1.5–2.5% |
| Heavy Metals | Lead, arsenic, mercury, cadmium — should pass USP limits | Pass / fail notation |
A mitragynine % of 1.2–1.8% indicates good-quality plain leaf powder. Values below 0.8% may indicate diluted or lower-potency material. 7-HMG values significantly above 0.02% in plain-leaf powder are a red flag for potential adulteration — naturally occurring 7-HMG in fresh-dried leaf rarely exceeds this threshold.[3] Avula et al. (2026) in Phytochemistry quantified 7-HMG across a sample of commercial kratom products and examined its chemical stability under storage and physiological conditions — the paper is the most current empirical reference for what 7-HMG values in whole-leaf powder should actually look like, and directly supports the “flag values well above natural leaf” guidance above.[11]
See the full guide: Kratom COA and Lab Testing Guide
Frequently asked questions about kratom alkaloids
How many alkaloids does kratom contain?
Kratom (Mitragyna speciosa) leaf contains over 40 naturally occurring alkaloids, primarily monoterpenoid indole alkaloids. The two most studied are mitragynine (~66% of total alkaloids) and 7-hydroxymitragynine (<2%). The remaining alkaloids — speciociliatine, paynantheine, speciogynine, corynantheidine, mitraphylline, rhynchophylline, and others — are present in smaller quantities but contribute to the plant’s overall pharmacological profile.[1]
Is mitragynine the same as 7-hydroxymitragynine?
No. Mitragynine is the parent compound — the most abundant alkaloid in the leaf. 7-Hydroxymitragynine (7-HMG) is produced when CYP3A4 enzymes in the liver convert mitragynine metabolically. Despite being present naturally at under 2% in the leaf, 7-HMG is estimated to be approximately 13 times more potent than morphine at mu-opioid receptors in animal models, making it a key contributor to kratom’s analgesic effects.[3]
What is the entourage effect in kratom?
The “entourage effect” is the hypothesis that multiple alkaloids in the whole plant interact synergistically or antagonistically to produce effects different from any single alkaloid in isolation. In kratom, this is suggested by: corynantheidine’s potential opioid receptor antagonism modulating mitragynine’s agonism; minor alkaloids contributing muscle relaxant or anxiolytic activity; and the observation that isolated mitragynine produces a different subjective experience than whole-leaf kratom at equivalent mitragynine doses. This remains a hypothesis under active research, not a proven clinical mechanism.[1]
Does higher mitragynine percentage mean stronger kratom?
Not necessarily. Mitragynine percentage is one variable — but the full alkaloid profile, including minor alkaloids and the mitragynine-to-7-HMG ratio, shapes overall effects. Two products with identical mitragynine percentages but different minor alkaloid profiles can feel meaningfully different. Additionally, individual CYP3A4 activity affects how much 7-HMG each person generates from a given dose — contributing to person-to-person variability in the same product.[3]
Why is 7-HMG content important to check on a COA?
Naturally occurring 7-HMG in dried kratom leaf rarely exceeds 0.02% by weight. Researchers have documented commercial kratom products with 7-HMG levels far above this range — indicating deliberate adulteration, since higher 7-HMG content significantly increases potency and dependence risk[8]. Any COA showing 7-HMG above ~0.1% in a plain-leaf powder product warrants close scrutiny and caution.[3]
Can kratom alkaloids cause drug interactions?
Yes — this is clinically significant. Multiple kratom alkaloids inhibit CYP3A4, CYP2D6, CYP2C9, and CYP1A2 enzymes.[2][6] These enzymes metabolize a wide range of prescription medications. CYP inhibition can increase plasma concentrations of co-administered drugs, with potential for increased effects or toxicity. Users on prescription medications should disclose kratom use to their prescribing physician before combining it with any medication.
Do different kratom strains have different alkaloid profiles?
Yes, with caveats. Vein color correlates with harvest maturity and generally reflects alkaloid profile differences — white vein (young leaf) tends toward higher mitragynine relative to total alkaloids; red vein (mature leaf) typically has higher overall alkaloid density. Published HPLC analyses confirm significant variation across strain categories. However, growing region, soil, drying method, and blending introduce additional variability, making strain labels imprecise alkaloid predictors. Batch-specific COA data is more reliable than strain names alone.[1]
What alkaloids cause kratom’s stimulant effects at low doses?
At low doses, kratom’s stimulant effects are primarily mediated by mitragynine’s activity at alpha-2 adrenergic receptors and 5-HT₂A receptors — not by opioid receptor activation, which predominates at higher doses.[4] This is why low-dose kratom produces effects subjectively similar to a strong stimulant — increased energy, alertness, and focus — while high doses shift toward sedation and analgesia as opioid receptor activity becomes dominant.
References
- Kruegel AC, Grundmann O. The medicinal chemistry and neuropharmacology of kratom. Neuropharmacology. 2018.
- Hanapi NA, et al. Kratom alkaloids: Interactions with enzymes, receptors, and cellular barriers. Front Pharmacol. 2021.
- Kruegel AC, et al. 7-Hydroxymitragynine is an active metabolite of mitragynine and a key mediator of its analgesic effects. ACS Cent Sci. 2019.
- Suhaimi FW, et al. Neurobiology of kratom and its main alkaloid mitragynine. Brain Res Bull. 2016.
- Trakulsrichai S, et al. Pharmacokinetics of mitragynine in man. Drug Des Devel Ther. 2015.
- Kong WM, et al. Evaluation of the effects of Mitragyna speciosa alkaloid extract on cytochrome P450 enzymes. Molecules. 2011.
- Prozialeck WC, Avery BA, Boyer EW, et al. Kratom policy: The challenge of balancing therapeutic potential with public safety. Int J Drug Policy. 2019.
- Hemby SE, McIntosh S, Leon F, et al. (2019). Abuse liability and therapeutic potential of the Mitragyna speciosa (kratom) alkaloids mitragynine and 7-hydroxymitragynine. Addiction biology, 24(5), 874-885. [PubMed]
- Kamble SH, et al. Metabolism of speciociliatine, an overlooked kratom alkaloid for its potential pharmacological effects. AAPS J. 2022.
- Obeng S, et al. Interactive effects of µ-opioid and adrenergic-α(2) receptor agonists in rats: pharmacological investigation of the primary kratom alkaloid mitragynine and its metabolite 7-hydroxymitragynine. J Pharmacol Exp Ther. 2022.
- Avula B, et al. Quantitative analysis of 7-hydroxymitragynine in commercial kratom products and its stability under chemical and physiological conditions. Phytochemistry. 2026.
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