Paynantheine

Paynantheine at a Glance

Paynantheine is a corynanthe-type monoterpene indole alkaloid and the second most abundant alkaloid in the leaf of kratom (Mitragyna speciosa) — commonly quoted at around 8-9% of the total alkaloid fraction, behind mitragynine and roughly level with speciogynine ^{2Reference 2Chear NJ et al. · 2021In vitroExploring the chemistry of alkaloids from Malaysian Mitragyna speciosa (kratom) and the role of oxindoles on human opioid receptors — in vitroView study →}. Structurally it is mitragynine’s 3-dehydro relative: the same 9-methoxy corynanthe skeleton with a vinyl group in place of the ethyl side chain, which also makes it the dehydro analogue of speciogynine ^{19Reference 19Flores-Bocanegra L et al. · 2020The chemistry of kratom [Mitragyna speciosa]: updated characterization data and methods to elucidate indole and oxindole alkaloidsView study →}.

It is the clearest case in the kratom alkaloid set of abundance without potency. At the mu-opioid receptor its affinity is about 410 nM — roughly 2.5 times weaker than mitragynine and about a hundred times weaker than morphine ^{2,3Reference 2Chear NJ et al. · 2021In vitroExploring the chemistry of alkaloids from Malaysian Mitragyna speciosa (kratom) and the role of oxindoles on human opioid receptors — in vitroView study →Reference 3Obeng S et al. · 2020In vitroInvestigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloids — in vitro and in ratsView study →} — and in mice it produces no meaningful antinociception on its own, instead blocking morphine’s ^{6Reference 6Gutridge AM et al. · 2021In vitroEvaluation of kratom opioid derivatives as potential treatment option for alcohol use disorder — in vitro and in miceView study →}. Its best-characterised activity is not opioid at all but serotonergic: paynantheine binds 5-HT1A and 5-HT2B receptors with high affinity where mitragynine does not, and produces 5-HT1A-mediated behavioural effects in rats through its 9-O-desmethyl metabolite ^{5Reference 5León F et al. · 2021In vitroActivity of Mitragyna speciosa (“kratom”) alkaloids at serotonin receptors — in vitro and in ratsView study →}.

This page is a scholarly pharmacology and toxicology reference for the isolated molecule. It gives no dose for effect and no preparation, extraction or synthesis guidance. The honest summary of the evidence base is that it is thin and almost entirely preclinical — a handful of receptor-binding studies, one rodent behavioural paper, some pharmacokinetics obtained inside whole-kratom dosing, and a large analytical literature that treats paynantheine mainly as a marker molecule for detecting kratom use.

Abundance Without Potency

If you assume the second-most-abundant compound in a plant is the second-most-important one, kratom is the counterexample. Paynantheine is present at roughly eight to nine times the level of 7-hydroxymitragynine — and 7-hydroxymitragynine, at under 2% of the alkaloid fraction, is the constituent that carries most of kratom’s opioid effect and essentially all of its abuse liability. Paynantheine, at 8-9%, carries very little of either.

Three measurements make the point:

Alkaloid	Approx. share of alkaloid fraction	Mu-opioid Kᵢ
Mitragynine	~66%	161 nM 2Reference 2Chear NJ et al. · 2021In vitroExploring the chemistry of alkaloids from Malaysian Mitragyna speciosa (kratom) and the role of oxindoles on human opioid receptors — in vitroView study →
Paynantheine	~8-9%	410 nM 2,3Reference 2Chear NJ et al. · 2021In vitroExploring the chemistry of alkaloids from Malaysian Mitragyna speciosa (kratom) and the role of oxindoles on human opioid receptors — in vitroView study →Reference 3Obeng S et al. · 2020In vitroInvestigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloids — in vitro and in ratsView study →
Speciogynine	~7%	728 nM 2Reference 2Chear NJ et al. · 2021In vitroExploring the chemistry of alkaloids from Malaysian Mitragyna speciosa (kratom) and the role of oxindoles on human opioid receptors — in vitroView study →
Speciociliatine	~1-3%	54.5 nM 2Reference 2Chear NJ et al. · 2021In vitroExploring the chemistry of alkaloids from Malaysian Mitragyna speciosa (kratom) and the role of oxindoles on human opioid receptors — in vitroView study →
Morphine (reference)	—	4.19 nM 2Reference 2Chear NJ et al. · 2021In vitroExploring the chemistry of alkaloids from Malaysian Mitragyna speciosa (kratom) and the role of oxindoles on human opioid receptors — in vitroView study →

The pattern is that abundance and mu-affinity are close to uncorrelated across the kratom alkaloids: speciociliatine is a minor constituent with the strongest mu binding of the four, and paynantheine is a major constituent with among the weakest. Kratom’s pharmacology is therefore not a simple weighted sum of its alkaloids, and a product’s paynantheine content tells you very little about how opioid-like it will be.

Two further facts blunt paynantheine’s contribution even at 8-9%. First, in vivo it behaves less like an agonist than a weak competitor: in mice, 30 mg/kg blocked morphine’s antinociception rather than producing its own, and the authors concluded it is “a weak partial agonist at the μOR and δOR, with functional antagonistic activity at the µOR in the presence of a more potent agonist” ^{6Reference 6Gutridge AM et al. · 2021In vitroEvaluation of kratom opioid derivatives as potential treatment option for alcohol use disorder — in vitro and in miceView study →}. Second, its systemic exposure after an oral kratom dose is short-lived — in rats it was quantifiable only up to one hour post-dose, while mitragynine and speciociliatine were still measurable at eight ^{10Reference 10Kamble SH et al. · 2021AnimalPharmacokinetics of eleven kratom alkaloids following an oral dose of either traditional or commercial kratom products in ratsView study →}.

Paynantheine & Its Diastereomers

Kratom carries several molecules of the same mass that differ only in stereochemistry, and separating them is most of the analytical difficulty in this plant. Nineteen alkaloids have been fully re-characterised by modern NMR and ECD for exactly this reason ^{19Reference 19Flores-Bocanegra L et al. · 2020The chemistry of kratom [Mitragyna speciosa]: updated characterization data and methods to elucidate indole and oxindole alkaloidsView study →}.

• Speciogynine is paynantheine’s saturated counterpart — paynantheine is the 3-dehydro (vinyl) analogue of it. The two track each other closely in the leaf, at roughly equal abundance, and share the high 5-HT1A/5-HT2B affinity that mitragynine lacks ^{5Reference 5León F et al. · 2021In vitroActivity of Mitragyna speciosa (“kratom”) alkaloids at serotonin receptors — in vitro and in ratsView study →}.
• Isopaynantheine is paynantheine’s 3R diastereomer, and pharmacologically a different animal: it is the first kratom-derived kappa-opioid agonist identified in vivo, with reduced β-arrestin-2 recruitment ^{26Reference 26Chakraborty S et al. · 2021In vitroKratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratom — in vitro and in miceView study →}. It is a separate molecule with a separate metabolic fate ^{13Reference 13Philipp AA et al. · 2011AnimalMetabolism studies of the kratom alkaloids mitraciliatine and isopaynantheine, diastereomers of the main alkaloids mitragynine and paynantheine, in rat and human urineView study →}, and none of its kappa pharmacology should be read onto paynantheine.
• Epiallo-isopaynantheine and the corresponding N(4)-oxides round out the family and were only formally characterised in 2020 ^{19Reference 19Flores-Bocanegra L et al. · 2020The chemistry of kratom [Mitragyna speciosa]: updated characterization data and methods to elucidate indole and oxindole alkaloidsView study →}.

The 3S/3R split is not cosmetic. In the first human pharmacokinetic study of kratom, the 3S alkaloids (mitragynine, speciogynine, paynantheine) behaved as one group and the 3R alkaloids (mitraciliatine, speciociliatine, isopaynantheine) as another, with markedly different distribution volumes, clearances, AUCs and half-lives ^{9Reference 9Tanna RS et al. · 2022Clinical trialClinical pharmacokinetic assessment of kratom (Mitragyna speciosa), a botanical product with opioid-like effects, in healthy adult participants — human studyView study →}. Stereochemistry, not abundance, is what sorts these molecules kinetically.

Vein Colour & the Alkaloid Fingerprint

Consumer kratom is sold by leaf-vein colour — red, green, white — with the near-universal claim that the colour signals a different alkaloid ratio and therefore a different effect. That claim does not survive checking.

Two independent studies tested it directly and found no difference:

• A survey of 611 Thai kratom samples (57% green-veined, 29% red-veined) compared mitragynine, paynantheine and speciogynine content between red- and green-veined plants and reported alkaloid production similar in both leaf types, without significant differences. The authors suggested vein colour probably reflects soil type and nutrients rather than a genetic or chemical distinction ^{1Reference 1Sengnon N et al. · 2023Seasonal and geographic variation in alkaloid content of kratom (Mitragyna speciosa (Korth.) Havil.) from ThailandView study →}.
• A 2026 study of eight Thai accessions selected for visible variation in leaf morphology and vein colouration, genotyped by four DNA barcodes and profiled for 17 alkaloids, found that “despite visible distinction in leaf vein coloration, alkaloid profiles at maturity remained largely consistent across all accessions.” Leaf developmental stage mattered far more than accession or haplotype — juvenile leaves accumulated speciociliatine as the dominant alkaloid while mature leaves accumulated mitragynine ^{20Reference 20Ransden KE et al. · 2026Comparative analysis of monoterpene indole alkaloid composition and genotypic variation in Thai Mitragyna speciosaView study →}.

What does move the paynantheine ratio is real, just not the thing being sold:

• Geography. The mitragynine:paynantheine:speciogynine ratio runs about 7:1:1 in Thai material, about 10:1:1 in Malaysian material, and roughly 0.2:0.2:1 in US-grown plants — where speciogynine, not mitragynine, is the dominant alkaloid ^{1,2,31Reference 1Sengnon N et al. · 2023Seasonal and geographic variation in alkaloid content of kratom (Mitragyna speciosa (Korth.) Havil.) from ThailandView study →Reference 2Chear NJ et al. · 2021In vitroExploring the chemistry of alkaloids from Malaysian Mitragyna speciosa (kratom) and the role of oxindoles on human opioid receptors — in vitroView study →Reference 31León F et al. · 2009Phytochemical characterization of the leaves of Mitragyna speciosa grown in U.S.AView study →}. US-grown M. speciosa is effectively a different chemotype ^{18Reference 18Manwill PK et al. · 2022Kratom (Mitragyna speciosa) validation: quantitative analysis of indole and oxindole alkaloids reveals chemotypes of plants and productsView study →}.
• Season and harvest timing. Alkaloid accumulation in Thai leaf peaked in the June-August collection and was lowest in the rainy season, with paynantheine contributing significantly to the difference in total alkaloid content between periods ^{1Reference 1Sengnon N et al. · 2023Seasonal and geographic variation in alkaloid content of kratom (Mitragyna speciosa (Korth.) Havil.) from ThailandView study →}.
• Post-harvest handling. In the cultivar ‘Hawaii’, 12 hours of withering followed by drying below 40 °C raised paynantheine by 35-67% ^{21Reference 21Zhang M et al. · 2025Alkaloid biosynthesis in medicinal crop kratom (Mitragyna speciosa) varies with postharvest, genetic, and seasonal factorsView study →}. How the leaf is dried shifts the fingerprint more than any colour label.

The practical reading: paynantheine ratios are a genuine origin and processing signature, which is why forensic and product-authentication labs measure them ^{18,4Reference 18Manwill PK et al. · 2022Kratom (Mitragyna speciosa) validation: quantitative analysis of indole and oxindole alkaloids reveals chemotypes of plants and productsView study →Reference 4Sharma A et al. · 2019Simultaneous quantification of ten key kratom alkaloids in Mitragyna speciosa leaf extracts and commercial products by ultra-performance liquid chromatography-tandem mass spectrometryView study →} — but vein colour is not a proxy for them.

What It's Used For

The isolate literature on paynantheine is small. Almost all of it is receptor binding, one rodent behavioural paper, and pharmacokinetics measured inside whole-kratom dosing. There are no human studies of paynantheine as an isolated compound.

Evidence by IndicationStrength of support · Beta

Support is an experimental score — weighted by study type (human > animal > in vitro) and volume. A beta, not a validated metric. Every row here is preclinical; nothing here is supported by a human outcome study of the isolated molecule, so the whole scale sits low by design.

01Analytical marker of kratom exposurePromising48%Validated LC-MS/MS methods in urine, plasma, nail; metabolite mapping ^{11,12,23,24Reference 11Sempio C et al. · 2025Clinical trialQuantification of 11 kratom alkaloids including mitragynine and its main metabolites in human plasma using LC-MS/MS — clinical study samplesView study →Reference 12Philipp AA et al. · 2010AnimalUse of liquid chromatography coupled to low- and high-resolution linear ion trap mass spectrometry for studying the metabolism of paynantheine, an alkaloid of the herbal drug kratom, in rat and human urineView study →Reference 23Basiliere S et al. · 2018Identification of five Mitragyna alkaloids in urine using liquid chromatography-quadrupole/time of flight mass spectrometryView study →Reference 24Ameline A et al. · 2024Case reportTesting for kratom alkaloids in fingernail clippings — not only mitragynine; case reportView study →}

02Serotonergic (5-HT1A) activityShaky30%Isolate binding + rat behaviour, antagonist-blocked; metabolite-driven ^{5Reference 5León F et al. · 2021In vitroActivity of Mitragyna speciosa (“kratom”) alkaloids at serotonin receptors — in vitro and in ratsView study →}

03Opioid-receptor activityShaky22%Isolate binding (Kᵢ 410 nM) + mouse behaviour showing antagonism, not analgesia ^{2,3,6,7Reference 2Chear NJ et al. · 2021In vitroExploring the chemistry of alkaloids from Malaysian Mitragyna speciosa (kratom) and the role of oxindoles on human opioid receptors — in vitroView study →Reference 3Obeng S et al. · 2020In vitroInvestigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloids — in vitro and in ratsView study →Reference 6Gutridge AM et al. · 2021In vitroEvaluation of kratom opioid derivatives as potential treatment option for alcohol use disorder — in vitro and in miceView study →Reference 7Gutridge AM et al. · 2020In vitroG protein-biased kratom-alkaloids and synthetic carfentanil-amide opioids as potential treatments for alcohol use disorder — in vitro and in miceView study →}

04Multidrug-resistance reversalShaky12%One in-vitro/docking study in two resistant cancer lines ^{17Reference 17Abdali N et al. · 2024In vitroPaynantheine more effectively reverses multidrug resistance in malignant EPG85.257RDB and MCF7MX cells than morphine and speciociliatine — in vitroView study →}

05Smooth-muscle relaxationShaky5%Repeated in reviews and consumer sources; no primary isolate experiment located

Mechanisms

The load-bearing contrast is that paynantheine’s strongest receptor interactions are serotonergic, while its opioid interaction is weak enough that in the presence of a real opioid it behaves as a competitor. That is the opposite of what an 8-9% abundance share would lead you to expect.

Pharmacokinetics

Paynantheine has the unusual distinction of having been measured in humans without ever having been given to one. Every human number comes from whole-kratom dosing.

In the first comprehensive human kratom pharmacokinetic study — a single 2 g oral dose of a characterised product in six healthy participants — paynantheine grouped with the other 3S alkaloids (mitragynine, speciogynine): median Tmax 1-2 h, AUC 430-490 nM·h, terminal half-life 24-45 h, and a very large apparent terminal volume of distribution (960-12,700 L). The 3R alkaloids in the same subjects behaved quite differently — later Tmax, far higher AUC, shorter half-life and small volumes — with the difference attributed to differential hepatic/intestinal metabolism, plasma protein binding and blood-to-plasma partitioning ^{9Reference 9Tanna RS et al. · 2022Clinical trialClinical pharmacokinetic assessment of kratom (Mitragyna speciosa), a botanical product with opioid-like effects, in healthy adult participants — human studyView study →}. In rats given oral kratom, paynantheine and speciogynine were quantifiable only up to one hour post-dose, while mitragynine, 7-hydroxymitragynine, speciociliatine and corynantheidine were still measurable at eight — i.e. low and brief systemic exposure relative to abundance ^{10Reference 10Kamble SH et al. · 2021AnimalPharmacokinetics of eleven kratom alkaloids following an oral dose of either traditional or commercial kratom products in ratsView study →}. In a 15-day repeat-dose human study paynantheine was reliably quantifiable in plasma but, unlike mitragynine, speciogynine and speciociliatine, did not accumulate ^{11Reference 11Sempio C et al. · 2025Clinical trialQuantification of 11 kratom alkaloids including mitragynine and its main metabolites in human plasma using LC-MS/MS — clinical study samplesView study →}.

Metabolism is well mapped, and was worked out backwards. Investigators studying mitragynine kept finding unexplained “dehydro” analogues in the urine of kratom users that never appeared in rats dosed with pure mitragynine; administering purified paynantheine to rats showed these were paynantheine metabolites. Phase I products include 9-O-demethyl, 17-O-demethyl, 16-carboxy and 9,17-O-bisdemethyl paynantheine plus several 16,17-dihydro forms, many excreted as glucuronides or sulfates — the same pathways mitragynine uses ^{12Reference 12Philipp AA et al. · 2010AnimalUse of liquid chromatography coupled to low- and high-resolution linear ion trap mass spectrometry for studying the metabolism of paynantheine, an alkaloid of the herbal drug kratom, in rat and human urineView study →}. The 9-O-desmethyl metabolite is the pharmacologically interesting one, since it, not the parent, appears to drive the 5-HT1A effects ^{5Reference 5León F et al. · 2021In vitroActivity of Mitragyna speciosa (“kratom”) alkaloids at serotonin receptors — in vitro and in ratsView study →}.

Distribution into the brain is not the limiting step: in a PAMPA blood-brain-barrier assay, paynantheine — with mitragynine, speciogynine and speciociliatine — showed excellent in-vitro BBB permeability ^{22Reference 22Dohárszky A et al. · 2024In vitroKratom alkaloids: a blood-brain barrier specific membrane permeability assay-guided isolation and cyclodextrin complexation study — in vitroView study →}. The constraint is systemic exposure and receptor potency, not access.

Clinical Trials

None. There are no completed, ongoing or registered trials of isolated paynantheine, and no human study has administered it. Human data exist only as plasma and urine measurements taken inside whole-kratom pharmacokinetic and forensic studies ^{9,11,12Reference 9Tanna RS et al. · 2022Clinical trialClinical pharmacokinetic assessment of kratom (Mitragyna speciosa), a botanical product with opioid-like effects, in healthy adult participants — human studyView study →Reference 11Sempio C et al. · 2025Clinical trialQuantification of 11 kratom alkaloids including mitragynine and its main metabolites in human plasma using LC-MS/MS — clinical study samplesView study →Reference 12Philipp AA et al. · 2010AnimalUse of liquid chromatography coupled to low- and high-resolution linear ion trap mass spectrometry for studying the metabolism of paynantheine, an alkaloid of the herbal drug kratom, in rat and human urineView study →}. Systematic reviews of kratom in humans cover the plant and mitragynine, not this alkaloid ^{32Reference 32Prevete E et al. · 2022Systematic reviewA systematic review of (pre)clinical studies on the therapeutic potential and safety profile of kratom in humansView study →}.

Last checked: July 2026.

Isolate vs. Plant Studies

This molecule sits in an unusual position: the mechanistic work is genuinely on the isolate, and the human work is entirely on the plant.

The isolate side is real. Paynantheine has been isolated from kratom leaf and administered as a pure compound to rats for the metabolism study ^{12Reference 12Philipp AA et al. · 2010AnimalUse of liquid chromatography coupled to low- and high-resolution linear ion trap mass spectrometry for studying the metabolism of paynantheine, an alkaloid of the herbal drug kratom, in rat and human urineView study →}, to rats for the serotonin-receptor behavioural work ^{5Reference 5León F et al. · 2021In vitroActivity of Mitragyna speciosa (“kratom”) alkaloids at serotonin receptors — in vitro and in ratsView study →}, and to mice for the opioid behavioural work ^{6Reference 6Gutridge AM et al. · 2021In vitroEvaluation of kratom opioid derivatives as potential treatment option for alcohol use disorder — in vitro and in miceView study →}; it has been assayed as purified material for mu-opioid binding ^{2,3Reference 2Chear NJ et al. · 2021In vitroExploring the chemistry of alkaloids from Malaysian Mitragyna speciosa (kratom) and the role of oxindoles on human opioid receptors — in vitroView study →Reference 3Obeng S et al. · 2020In vitroInvestigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloids — in vitro and in ratsView study →}, hERG current ^{15Reference 15Lu J et al. · 2014In vitroEvaluation of the cardiotoxicity of mitragynine and its analogues using human induced pluripotent stem cell-derived cardiomyocytes — in vitroView study →}, CYP inhibition ^{14Reference 14Kamble SH et al. · 2020In vitroExploration of cytochrome P450 inhibition mediated drug-drug interaction potential of kratom alkaloids — in vitro, human liver microsomesView study →} and hepatocyte cytotoxicity ^{16Reference 16Karunakaran T et al. · 2025In-vitro hepatotoxic activity of mitragynine and paynantheine isolated from the leaves of Mitragyna speciosa Korth. (kratom)View study →}. That is a stronger isolate base than many plant constituents get.

The plant side is where the humans are. Every human measurement of paynantheine — the six-participant pharmacokinetic study ^{9Reference 9Tanna RS et al. · 2022Clinical trialClinical pharmacokinetic assessment of kratom (Mitragyna speciosa), a botanical product with opioid-like effects, in healthy adult participants — human studyView study →}, the 15-day repeat-dose plasma work ^{11Reference 11Sempio C et al. · 2025Clinical trialQuantification of 11 kratom alkaloids including mitragynine and its main metabolites in human plasma using LC-MS/MS — clinical study samplesView study →}, the urine metabolite mapping ^{12Reference 12Philipp AA et al. · 2010AnimalUse of liquid chromatography coupled to low- and high-resolution linear ion trap mass spectrometry for studying the metabolism of paynantheine, an alkaloid of the herbal drug kratom, in rat and human urineView study →}, the fingernail case ^{24Reference 24Ameline A et al. · 2024Case reportTesting for kratom alkaloids in fingernail clippings — not only mitragynine; case reportView study →} — comes from people who consumed whole kratom, in which paynantheine is a minority component alongside a dominant mitragynine. The transferability problem therefore runs in the usual direction: nothing observed in a kratom user can be attributed to paynantheine, and given its weak mu affinity, its in-vivo antagonism of morphine, and its brief systemic exposure, the reasonable prior is that it contributes little to what kratom does. The one caveat is its 5-HT1A metabolite, which is the plausible route by which an abundant but opioid-weak alkaloid could still matter ^{5Reference 5León F et al. · 2021In vitroActivity of Mitragyna speciosa (“kratom”) alkaloids at serotonin receptors — in vitro and in ratsView study →}.

Paynantheine as an Analytical Marker

Paynantheine’s most reliable role is forensic and analytical. Because mitragynine alone can be ambiguous — it degrades, it is the target of adulteration, and it does not describe a product’s origin — paynantheine is routinely included as a co-marker.

• Detecting use. Validated methods quantify it in urine ^{23Reference 23Basiliere S et al. · 2018Identification of five Mitragyna alkaloids in urine using liquid chromatography-quadrupole/time of flight mass spectrometryView study →}, plasma ^{11Reference 11Sempio C et al. · 2025Clinical trialQuantification of 11 kratom alkaloids including mitragynine and its main metabolites in human plasma using LC-MS/MS — clinical study samplesView study →}, and fingernail clippings ^{24Reference 24Ameline A et al. · 2024Case reportTesting for kratom alkaloids in fingernail clippings — not only mitragynine; case reportView study →}. Its distinctive dehydro metabolites are what allowed kratom-specific ingestion to be distinguished from pure mitragynine exposure ^{12Reference 12Philipp AA et al. · 2010AnimalUse of liquid chromatography coupled to low- and high-resolution linear ion trap mass spectrometry for studying the metabolism of paynantheine, an alkaloid of the herbal drug kratom, in rat and human urineView study →}.
• Authenticating product. Paynantheine is one of the alkaloids used to fingerprint commercial powders, teas, liquid shots and alkaloid partitions, where its concentration varies enormously between products ^{18,4Reference 18Manwill PK et al. · 2022Kratom (Mitragyna speciosa) validation: quantitative analysis of indole and oxindole alkaloids reveals chemotypes of plants and productsView study →Reference 4Sharma A et al. · 2019Simultaneous quantification of ten key kratom alkaloids in Mitragyna speciosa leaf extracts and commercial products by ultra-performance liquid chromatography-tandem mass spectrometryView study →}.
• Chemotaxonomy. In a metabolomic comparison of four Mitragyna species growing in Thailand, paynantheine was among the significant discriminants separating M. speciosa from M. hirsuta, M. diversifolia and M. rotundifolia — it is effectively a kratom-species marker, not a genus-wide one ^{25Reference 25Andriyas T et al. · 2025Interspecific and environmental influence on the foliar metabolomes of Mitragyna species through recursive OPLS-DA modelingView study →}.
• Tissue localisation. High-resolution imaging mass spectrometry resolved paynantheine from its isobaric interferences and mapped it throughout kratom twig tissue except the xylem ^{30Reference 30Wisanpitayakorn P et al. · 2025Spatial mapping of stereoisomeric and isobaric alkaloids in Mitragyna speciosa tissues by high-resolution DESI-cIM-MSView study →}.

A practical caution runs through all of this: paynantheine is one of a set of isobaric, near-isobaric and stereoisomeric alkaloids, and methods that do not chromatographically or ion-mobility-resolve them will mis-assign it ^{19,30Reference 19Flores-Bocanegra L et al. · 2020The chemistry of kratom [Mitragyna speciosa]: updated characterization data and methods to elucidate indole and oxindole alkaloidsView study →Reference 30Wisanpitayakorn P et al. · 2025Spatial mapping of stereoisomeric and isobaric alkaloids in Mitragyna speciosa tissues by high-resolution DESI-cIM-MSView study →}.

Its Role in Plants

Paynantheine is a monoterpene indole alkaloid, built from the same strictosidine-derived pathway that produces mitragynine and the rest of kratom’s corynanthe-type alkaloids. Its 9-methoxy corynanthe skeleton is shared with mitragynine and speciogynine, and the three are usually discussed together as the plant’s dominant 3S indoles ^{2,19Reference 2Chear NJ et al. · 2021In vitroExploring the chemistry of alkaloids from Malaysian Mitragyna speciosa (kratom) and the role of oxindoles on human opioid receptors — in vitroView study →Reference 19Flores-Bocanegra L et al. · 2020The chemistry of kratom [Mitragyna speciosa]: updated characterization data and methods to elucidate indole and oxindole alkaloidsView study →}.

Where the pathway sits in the plant is now partly mapped. Strictosidine — the central precursor of monoterpene indole alkaloid biosynthesis — is detectable only in juvenile leaves, which also carry higher levels of upstream intermediates such as corynantheidine; mature leaves accumulate the downstream 3S alkaloids instead ^{20Reference 20Ransden KE et al. · 2026Comparative analysis of monoterpene indole alkaloid composition and genotypic variation in Thai Mitragyna speciosaView study →}. Imaging mass spectrometry places paynantheine throughout twig tissue except the xylem, a distribution the authors read as reflecting distinct biosynthesis, transport and storage roles among the alkaloids rather than passive diffusion ^{30Reference 30Wisanpitayakorn P et al. · 2025Spatial mapping of stereoisomeric and isobaric alkaloids in Mitragyna speciosa tissues by high-resolution DESI-cIM-MSView study →}.

Its ecological function is not established. The usual assumption for indole alkaloids in Rubiaceae is herbivore deterrence, but no experiment has tested paynantheine specifically in that role.

Prevalence in Nature

Paynantheine is, for practical purposes, a kratom molecule. It has not been reported as a meaningful constituent of any plant outside Mitragyna speciosa, and in a four-species metabolomic survey it was one of the compounds that separated M. speciosa from its congeners ^{25Reference 25Andriyas T et al. · 2025Interspecific and environmental influence on the foliar metabolomes of Mitragyna species through recursive OPLS-DA modelingView study →}.

In the leaf. Across 20 sites spanning northern, central and southern Thailand, paynantheine ranged 0.11-0.31% of dried leaf weight (median ≈0.20%), against mitragynine’s 0.48-2.03% in the same samples ^{1Reference 1Sengnon N et al. · 2023Seasonal and geographic variation in alkaloid content of kratom (Mitragyna speciosa (Korth.) Havil.) from ThailandView study →}. Expressed as a share of the alkaloid fraction it sits at roughly 8-9% — paynantheine and speciogynine together account for about 16% of total alkaloids ^{2Reference 2Chear NJ et al. · 2021In vitroExploring the chemistry of alkaloids from Malaysian Mitragyna speciosa (kratom) and the role of oxindoles on human opioid receptors — in vitroView study →}. The mitragynine:paynantheine:speciogynine ratio was approximately 7:1:1 in 19 of 20 Thai samples ^{1Reference 1Sengnon N et al. · 2023Seasonal and geographic variation in alkaloid content of kratom (Mitragyna speciosa (Korth.) Havil.) from ThailandView study →}.

Geographic chemotypes. Malaysian material runs closer to 10:1:1 ^{1,2Reference 1Sengnon N et al. · 2023Seasonal and geographic variation in alkaloid content of kratom (Mitragyna speciosa (Korth.) Havil.) from ThailandView study →Reference 2Chear NJ et al. · 2021In vitroExploring the chemistry of alkaloids from Malaysian Mitragyna speciosa (kratom) and the role of oxindoles on human opioid receptors — in vitroView study →}. US-grown M. speciosa is a different chemotype entirely — roughly 0.2:0.2:1, with speciogynine dominant and mitragynine sometimes below the quantification limit ^{1,18,31Reference 1Sengnon N et al. · 2023Seasonal and geographic variation in alkaloid content of kratom (Mitragyna speciosa (Korth.) Havil.) from ThailandView study →Reference 18Manwill PK et al. · 2022Kratom (Mitragyna speciosa) validation: quantitative analysis of indole and oxindole alkaloids reveals chemotypes of plants and productsView study →Reference 31León F et al. · 2009Phytochemical characterization of the leaves of Mitragyna speciosa grown in U.S.AView study →}. Even within one Malaysian plantation, trees of similar age collected the same day differed sharply, with two samples showing no quantifiable mitragynine and low paynantheine but elevated speciociliatine ^{2Reference 2Chear NJ et al. · 2021In vitroExploring the chemistry of alkaloids from Malaysian Mitragyna speciosa (kratom) and the role of oxindoles on human opioid receptors — in vitroView study →}.

Season, nutrition and handling. Alkaloid accumulation in Thai leaf peaked in June-August and was lowest in the rainy season, with paynantheine significantly affecting total alkaloid content between collection periods; soil calcium and magnesium correlated with alkaloid production ^{1Reference 1Sengnon N et al. · 2023Seasonal and geographic variation in alkaloid content of kratom (Mitragyna speciosa (Korth.) Havil.) from ThailandView study →}. Post-harvest, 12 hours of withering followed by drying below 40 °C raised paynantheine 35-67% in one cultivar, and low drying temperatures preserved it across cultivars ^{21Reference 21Zhang M et al. · 2025Alkaloid biosynthesis in medicinal crop kratom (Mitragyna speciosa) varies with postharvest, genetic, and seasonal factorsView study →}. Leaf developmental stage is a further axis — juvenile and mature leaves carry different alkaloid balances ^{20Reference 20Ransden KE et al. · 2026Comparative analysis of monoterpene indole alkaloid composition and genotypic variation in Thai Mitragyna speciosaView study →}.

In products. Commercial powders, teas and alkaloid extracts span 0.3-12.8% w/w paynantheine, the top of that range reflecting concentrated alkaloid fractions rather than leaf ^{4Reference 4Sharma A et al. · 2019Simultaneous quantification of ten key kratom alkaloids in Mitragyna speciosa leaf extracts and commercial products by ultra-performance liquid chromatography-tandem mass spectrometryView study →}; across a separate product set the levels “varied in concentration from product to product” ^{18Reference 18Manwill PK et al. · 2022Kratom (Mitragyna speciosa) validation: quantitative analysis of indole and oxindole alkaloids reveals chemotypes of plants and productsView study →}.

Discovery & Synthesis

Paynantheine emerged from the mid-1960s effort by A. H. Beckett, E. J. Shellard, J. D. Phillipson and C. M. Lee at Chelsea College, London, who systematically resolved the alkaloid complement of Mitragyna speciosa and its Asian congeners. Their 1965 note in the Journal of Pharmacy and Pharmacology ^{28Reference 28Beckett AH et al. · 1965Alkaloids from Mitragyna speciosa (Korth.)View study →} and the fuller 1966 account in Planta Medica — “The Mitragyna species of Asia. VII. Indole alkaloids from the leaves of Mitragyna speciosa Korth.” ^{29Reference 29Beckett AH et al. · 1966The Mitragyna species of AsiaView study →} — are the papers in which the mitragynine-related indoles, paynantheine among them, were first described. The name follows the plant-alkaloid convention of the series rather than any pharmacological property.

Total synthesis came much later. In 2012, Kerschgens, Claveau, Wanner, Ingemann, van Maarseveen and Hiemstra in Amsterdam prepared (-)-mitragynine, (+)-paynantheine and (+)-speciogynine in nine steps from 4-methoxytryptamine, using an enantioselective thiourea-catalysed Pictet-Spengler reaction to build the tetrahydro-β-carboline core and a palladium-catalysed Tsuji-Trost allylic alkylation to close the D-ring ^{27Reference 27Kerschgens IP et al. · 2012Total syntheses of mitragynine, paynantheine and speciogynine via an enantioselective thiourea-catalysed Pictet-Spengler reactionView study →}. This is the reference synthesis for the family.

Today, paynantheine reaching researchers is isolated from kratom leaf, not synthesised — the standard route is chromatographic purification of an alkaloid-enriched leaf extract, which is how the reference standards used in the binding, metabolism and analytical studies above were obtained ^{2,12,22Reference 2Chear NJ et al. · 2021In vitroExploring the chemistry of alkaloids from Malaysian Mitragyna speciosa (kratom) and the role of oxindoles on human opioid receptors — in vitroView study →Reference 12Philipp AA et al. · 2010AnimalUse of liquid chromatography coupled to low- and high-resolution linear ion trap mass spectrometry for studying the metabolism of paynantheine, an alkaloid of the herbal drug kratom, in rat and human urineView study →Reference 22Dohárszky A et al. · 2024In vitroKratom alkaloids: a blood-brain barrier specific membrane permeability assay-guided isolation and cyclodextrin complexation study — in vitroView study →}. Because it is an abundant leaf alkaloid, extraction remains far cheaper than a nine-step synthesis. No commercial-scale production of the isolated molecule exists; its market is analytical reference standards.

Patents: not yet researched.

Legal Status

Paynantheine itself is not a scheduled substance in any major jurisdiction — it is regulated only indirectly, through the legal status of the plant it comes from.

Kratom’s status is fragmented and changes often. It is banned outright in a number of countries, including Myanmar, Australia, New Zealand and South Korea, among others ^{1Reference 1Sengnon N et al. · 2023Seasonal and geographic variation in alkaloid content of kratom (Mitragyna speciosa (Korth.) Havil.) from ThailandView study →}. Thailand decriminalised kratom in 2021, after which large-scale sampling of Thai plantations became possible for the first time ^{1Reference 1Sengnon N et al. · 2023Seasonal and geographic variation in alkaloid content of kratom (Mitragyna speciosa (Korth.) Havil.) from ThailandView study →}. In the United States kratom is federally unscheduled but is prohibited or restricted by several states and municipalities, and is the subject of ongoing regulatory attention — particularly concentrated 7-hydroxymitragynine products, which are pharmacologically nothing like leaf. Systematic reviews of the human literature repeatedly note that the regulatory picture has moved faster than the evidence ^{32Reference 32Prevete E et al. · 2022Systematic reviewA systematic review of (pre)clinical studies on the therapeutic potential and safety profile of kratom in humansView study →}.

Anyone handling paynantheine as an analytical standard or research chemical should assume local kratom law governs, and check it. Nothing here is legal advice.

Toxicity & Safety

Paynantheine carries a moderate flag. It is not acutely poisonous, shows no reward liability in animals, and has only weak cytotoxicity — but three preclinical findings keep it above “low”, and they are the reasons below. The wider point is that almost nothing is known about this molecule in humans on its own, so absence of reported harm is not evidence of safety.

Cardiac (hERG / I_Kr) Signal

The most substantive safety finding. In human induced-pluripotent-stem-cell-derived cardiomyocytes, mitragynine, paynantheine, speciogynine and speciociliatine all dose-dependently suppressed the rapid delayed-rectifier potassium current (I_Kr) by 67-84%, with IC50 values across the set of 0.91-2.47 µM. Mitragynine at 10 µM prolonged action-potential duration and induced arrhythmia without affecting L-type calcium current, and the authors concluded the alkaloids “may potentiate Torsade de Pointes through inhibition of I_Kr in human cardiomyocytes” ^{15Reference 15Lu J et al. · 2014In vitroEvaluation of the cardiotoxicity of mitragynine and its analogues using human induced pluripotent stem cell-derived cardiomyocytes — in vitroView study →}. This is an in-vitro finding at micromolar concentrations, and whether ordinary kratom use reaches them is unresolved — but it is a class effect that includes paynantheine, not a mitragynine-only issue.

Seizure Signal in Mice

At 30 mg/kg (i.p.), paynantheine produced Racine level 1-2 convulsive behaviours in mice, equally in wild-type and delta-opioid-receptor knockouts — so the effect is not delta-mediated. The investigators specifically flagged that paynantheine’s usefulness “may be limited by its low potency in vivo, and seizure effects that are not δOR-mediated” ^{6Reference 6Gutridge AM et al. · 2021In vitroEvaluation of kratom opioid derivatives as potential treatment option for alcohol use disorder — in vitro and in miceView study →}. This is an injected rodent dose far above anything achieved by consuming leaf, but it is the clearest adverse signal in the isolate literature.

Drug Interactions (CYP450)

Paynantheine showed moderate inhibition of CYP2D6 — weaker than mitragynine (IC50 2.2 µM) or corynantheidine (4.2 µM), which were the potent inhibitors in that screen. It also inhibited CYP3A4/5 activity when midazolam was the probe substrate, but not when testosterone was — a substrate-dependent, site-specific inhibition ^{14Reference 14Kamble SH et al. · 2020In vitroExploration of cytochrome P450 inhibition mediated drug-drug interaction potential of kratom alkaloids — in vitro, human liver microsomesView study →}. The clinically consequential CYP2D6 interaction risk in kratom belongs mainly to mitragynine and corynantheidine; paynantheine adds to, rather than drives, it. Because CYP2D6 handles many antidepressants, antipsychotics, opioids and beta-blockers, and CYP3A4 handles a large share of everything else, this is the interaction axis to take seriously in a kratom user.

Cytotoxicity

Paynantheine isolated from kratom leaf showed only weak cytotoxicity against both the HepG2 hepatoma line and the normal HL-7702 liver line, compared with mitragynine’s moderate inhibition of HepG2 (IC50 42.11 µM) ^{16Reference 16Karunakaran T et al. · 2025In-vitro hepatotoxic activity of mitragynine and paynantheine isolated from the leaves of Mitragyna speciosa Korth. (kratom)View study →}. In resistant cancer lines it was more cytotoxic than morphine, which is being read there as a therapeutic signal rather than a hazard ^{17Reference 17Abdali N et al. · 2024In vitroPaynantheine more effectively reverses multidrug resistance in malignant EPG85.257RDB and MCF7MX cells than morphine and speciociliatine — in vitroView study →}. There is no repeat-dose, genotoxicity or reproductive-toxicity package for the isolated molecule; kratom’s own hepatotoxicity case literature concerns the whole product, not this alkaloid.

Reproductive note (prose only). No reproductive or developmental toxicity data exist for isolated paynantheine. Pregnancy and lactation decisions belong on the herb or product page where intake is actually decided, not on a molecule-level phytochemistry page.

Safety at a Glance

⚠️ Moderate toxicityCardiac cautionControlled substance

• No reward or dependence signal in animals. Paynantheine produced aversion rather than conditioned place preference in mice, and blocked rather than mimicked morphine’s effects.
• Cardiac potassium-channel (hERG/I_Kr) suppression in vitro. A class effect shared with mitragynine and the other major kratom indoles, with a theoretical QT-prolongation / Torsade risk.
• Convulsive behaviour in mice at a high injected dose (30 mg/kg), not delta-opioid-mediated.
• CYP2D6 and CYP3A4/5 inhibition. Moderate for this alkaloid, substantial for kratom as a whole — relevant to antidepressants, antipsychotics, opioids, beta-blockers and much else.
• Essentially no human safety data for the isolated molecule. Everything above is in vitro or rodent; nothing here should be read as a safety clearance.

Dosage

There is no dose of paynantheine. It has never been administered to a human as an isolated compound, has no established therapeutic use, and no recommended intake exists for any purpose. No dosing-for-effect information is given here.

For completeness, the figures that appear in the research literature are rodent research doses given by injection for mechanistic purposes:

Human exposure is only ever indirect, as a minority alkaloid within kratom leaf or a kratom product — roughly 0.11-0.31% of dried Thai leaf by weight ^{1Reference 1Sengnon N et al. · 2023Seasonal and geographic variation in alkaloid content of kratom (Mitragyna speciosa (Korth.) Havil.) from ThailandView study →}, and 0.3-12.8% w/w of commercial powders and extracts ^{4Reference 4Sharma A et al. · 2019Simultaneous quantification of ten key kratom alkaloids in Mitragyna speciosa leaf extracts and commercial products by ultra-performance liquid chromatography-tandem mass spectrometryView study →}. These are research figures and product analyses, not a personal recommendation.

References

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