Corynantheidine

Corynantheidine at a Glance

Corynantheidine is a minor indole alkaloid of kratom (Mitragyna speciosa) and, structurally, the plainest member of the family: it is mitragynine minus the methoxy group at position 9 — hence its other name, 9-desmethoxymitragynine ^{1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →}. It shares mitragynine’s stereochemistry at C3 and C20, so the only difference between the two molecules is one small substituent on the indole ring ^{1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →}.

That single missing group is why the compound matters. Kratom’s reputation rests on mu-opioid agonism, and corynantheidine has spent twenty years being described as the plant’s internal mu-opioid antagonist — the alkaloid working against the others. If true, that would be a striking piece of internal pharmacology. The primary literature turns out to be more interesting than the summary: the antagonist label comes from a single 2002 guinea-pig ileum experiment, and when the molecule was finally run through modern receptor assays in 2021 it behaved as a low-efficacy partial agonist that produced genuine, mu-dependent antinociception in mice ^{1,3Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →Reference 3Takayama H et al. · 2002Studies on the synthesis and opioid agonistic activities of mitragynine-related indole alkaloids: discovery of opioid agonists structurally different from other opioid ligandsView study →}. Both results are consistent — with a molecule of intermediate intrinsic efficacy that reads as antagonist or agonist depending on the assay.

Two other things are worth holding onto. Corynantheidine binds alpha-adrenergic receptors more tightly than opioid ones — the alpha-1D affinity is 131-fold higher than mitragynine’s ^{2Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →} — so calling it “an opioid alkaloid” already undersells it. And in the plant it is not a curiosity but a biosynthetic precursor: juvenile kratom leaves are rich in corynantheidine, and its level falls as mitragynine accumulates ^{9,10Reference 9Laforest LC et al. · 2023Metabolite and molecular characterization of Mitragyna speciosa identifies developmental and genotypic effects on monoterpene indole and oxindole alkaloid compositionView study →Reference 10Ransden KE et al. · 2026Comparative analysis of monoterpene indole alkaloid composition and genotypic variation in Thai Mitragyna speciosaView study →}. There is no human data of any kind on the isolated compound.

The Mu-Opioid Antagonist Question

This is the claim the page exists to test, so it is worth tracing to its source.

Where the antagonist label comes from. In 2002 Takayama and colleagues ran a structure–activity survey of mitragynine-related alkaloids in the electrically stimulated guinea-pig ileum — the standard opioid bioassay of the era. Corynantheidine showed no agonist action in that tissue and reversed morphine’s inhibition of twitch contraction, which is the textbook signature of a competitive antagonist ^{3Reference 3Takayama H et al. · 2002Studies on the synthesis and opioid agonistic activities of mitragynine-related indole alkaloids: discovery of opioid agonists structurally different from other opioid ligandsView study →}. That single finding is the origin of every later restatement: the pharmacokinetics paper that first quantified the alkaloid describes it as “a functional opioid antagonist” ^{5Reference 5King TI et al. · 2020Bioanalytical method development and validation of corynantheidine, a kratom alkaloid, using UPLC-MS/MS, and its application to preclinical pharmacokinetic studiesView study →}, as does the analytical-method paper from the same group ^{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 →}.

What the modern assays show. In 2021 Chakraborty and colleagues characterised corynantheidine properly for the first time, across mouse and human receptors ^{1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →}:

Assay	Result
Binding, mouse MOR	Ki = 57 nM — about 4× tighter than mitragynine (230 nM)
Binding, human MOR (independent panel)	Ki = 118–339 nM, depending on the panel 1,2Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →
[³⁵S]GTPγS, mouse MOR	Partial agonist, Emax = 74% (mitragynine 65%), ~30× less potent than DAMGO
BRET Gi-1, human MOR	Partial agonist, Emax = 37%, EC50 = 67 nM, ~20× less potent than DAMGO
Beta-arrestin-2, all subtypes	No measurable recruitment
KOR / DOR signalling	None — mu-selective
Mouse tail-withdrawal (i.c.v.)	Dose-dependent antinociception with a ceiling at ~50% of maximum possible effect; attenuated in mu-receptor knockout mice

The reconciliation. These are not contradictory findings; they are the same molecule read through different amplification. The guinea-pig ileum is an intact tissue with limited receptor reserve, and it was challenged with a full agonist. A ligand with low intrinsic efficacy occupies the receptor, fails to produce a response the tissue can register, and blocks the full agonist — so it scores as an antagonist. The GTPγS and BRET assays use receptor-overexpressing cell lines with far more signal amplification, where the same low efficacy becomes a measurable partial response. The two Emax values from the 2021 paper itself make the point: 74% in the more amplified GTPγS assay, 37% in the less amplified BRET assay ^{1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →}. The in-vivo ceiling — antinociception that plateaus at half of maximum — is exactly what partial agonism predicts.

The honest verdict. Corynantheidine is best described as a low-efficacy mu-opioid partial agonist, not an antagonist. But the antagonist label is not simply wrong: a low-efficacy partial agonist will functionally oppose a stronger agonist at the same receptor, which is what the ileum experiment demonstrated. The internal-antagonism story survives in a more precise form — corynantheidine is not an off-switch sitting in the leaf, it is a weak ligand competing for the same receptor as the strong ones. Whether that competition matters at the concentrations kratom leaf actually delivers is a separate and unanswered question (see Isolate vs. Plant Studies).

One caveat on the caveat: nobody has directly tested corynantheidine’s ability to antagonise a full agonist in the modern assay systems. The 2021 study measured agonism, not competitive blockade of DAMGO or morphine ^{1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →}. Until someone runs that experiment, the strength of the antagonism half of the story rests on the 2002 tissue work alone.

The C9 Substitution Ladder

Corynantheidine’s real value is as the unsubstituted rung of a four-member series that differs only in what sits at position 9 of the indole ring (and, for the last member, position 7). Reading the series together is the cleanest structure–activity story kratom has:

Alkaloid	Substitution	Mu affinity (Ki)	Functional profile
Corynantheidine	C9–H	118 nM 2Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study → / 57 nM 1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →	Low-efficacy partial agonist; historically read as antagonist 1,3Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →Reference 3Takayama H et al. · 2002Studies on the synthesis and opioid agonistic activities of mitragynine-related indole alkaloids: discovery of opioid agonists structurally different from other opioid ligandsView study →
9-Hydroxycorynantheidine	C9–OH	105 nM 2Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →	Partial agonist, mu-selective, naloxone-reversible 8Reference 8Matsumoto K et al. · 2006Partial agonistic effect of 9-hydroxycorynantheidine on mu-opioid receptor in the guinea-pig ileumView study →
Mitragynine	C9–OMe	161 nM 2Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study → / 230 nM 1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →	Partial agonist, G-protein-biased 17Reference 17Kruegel AC et al. · 2016Synthetic and receptor signaling explorations of the Mitragyna alkaloids: mitragynine as an atypical molecular framework for opioid receptor modulatorsView study →
7-Hydroxymitragynine	C9–OMe + C7–OH	7.2 nM 2Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →	Potent partial agonist; the efficacy-carrying metabolite 17Reference 17Kruegel AC et al. · 2016Synthetic and receptor signaling explorations of the Mitragyna alkaloids: mitragynine as an atypical molecular framework for opioid receptor modulatorsView study →

Two conclusions fall out. First, the C9 substituent barely touches mu affinity. Corynantheidine, 9-hydroxycorynantheidine and mitragynine bind mu within a two-fold band; docking work suggests the C9 position simply does not form a strong interaction in the mu pocket ^{2Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →}. The dramatic affinity jump belongs to C7 hydroxylation, not C9 — which is why 7-hydroxymitragynine, and not any C9 variant, is the potent one.

Second, C9 does control selectivity. Removing the methoxy group costs roughly a ten-fold loss of kappa affinity (mitragynine 198 nM → corynantheidine 1,910 nM), attributed to a lost hydrogen bond with Thr111 in the kappa receptor ^{2Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →} — and it gains a very large amount of alpha-adrenergic affinity (below). The 9-methoxy group, in other words, is less an efficacy switch than a selectivity dial.

The same skeleton also runs sideways. Oxidative rearrangement gives the pseudoindoxyls — mitragynine pseudoindoxyl and its corynantheidine counterpart — which are mu agonists with delta antagonism and no beta-arrestin-2 recruitment ^{16Reference 16Váradi A et al. · 2016Mitragynine/corynantheidine pseudoindoxyls as opioid analgesics with mu agonism and delta antagonism, which do not recruit beta-arrestin-2View study →}. Ring-contraction to the spiro-oxindole gives corynoxine and corynoxine B, which occur in kratom and in cat’s claw alongside rhynchophylline; corynoxine, remarkably, is a mu full agonist (Emax 136%) and roughly equipotent with morphine in mice ^{1,18Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →Reference 18Flores-Bocanegra L et al. · 2020The chemistry of kratom [Mitragyna speciosa]: updated characterization data and methods to elucidate indole and oxindole alkaloidsView study →}. The corynanthe core is unusually tolerant of efficacy tuning.

Adrenergic Activity

The least-quoted fact about corynantheidine is that it is arguably more an adrenergic ligand than an opioid one.

Screened across five alpha-adrenergic and four opioid targets, corynantheidine’s tightest single interaction was alpha-1D (Ki = 41.7 nM) — tighter than its mu affinity (118 nM), and 131-fold tighter than mitragynine at the same receptor (5,480 nM) ^{2Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →}. It was the only alkaloid in that panel with meaningful alpha-1 binding at all. An independent screen across ~50 CNS targets put its highest affinities at alpha-2A (74 nM) and NMDA (83 nM), with alpha-2C at 269 nM and mu at 339 nM — eleven non-opioid targets in total ^{1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →}.

The two panels disagree about which alpha subtype leads (alpha-1D versus alpha-2A), which is a normal cross-laboratory discrepancy and not resolved. What both agree on is the direction: adrenergic affinity exceeds opioid affinity, and this is the reverse of mitragynine’s profile ^{1,2Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →}.

There is a tidy structural rationale. Corynantheidine, lacking the 9-methoxy group, adopts a three-dimensional conformation closely resembling yohimbine — the classic alpha-adrenergic antagonist, which likewise carries no indole methoxy ^{2Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →}. On this reading, mitragynine’s methoxy group is what removes the ancestral adrenergic pharmacology of the corynanthe skeleton, and corynantheidine simply retains it.

The gap is functional data. Every adrenergic number above is binding affinity only — nobody has established whether corynantheidine acts as an agonist, antagonist or inverse agonist at any alpha subtype, or measured a downstream cardiovascular effect. Its mouse antinociception may well be partly adrenergic rather than purely opioid; the 2021 authors raise that possibility explicitly but did not test it ^{1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →}.

What It's Used For

The entire evidence base is preclinical, and most of it is one 2021 receptor-pharmacology paper plus two pharmacokinetic studies from a single laboratory. There is no human study of the isolated alkaloid.

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, so the ceiling is low by construction; read the per-row basis.

01Mu-Opioid Receptor ModulationShaky32%Binding + two functional assay systems + mu-KO confirmation, one modern paper ^{1,2,3Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →Reference 3Takayama H et al. · 2002Studies on the synthesis and opioid agonistic activities of mitragynine-related indole alkaloids: discovery of opioid agonists structurally different from other opioid ligandsView study →}

02Antinociception (Preclinical)Shaky24%Mouse tail-withdrawal, i.c.v. only, ceiling ~50% MPE ^{1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →}

03Adrenergic Receptor BindingShaky18%Two radioligand panels; binding only, no functional or in-vivo data ^{1,2Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →}

04Antileishmanial (In Vitro)Shaky12%Single in-vitro study, micromolar IC50, non-kratom source plant ^{19Reference 19Staerk D et al. · 2000Leishmanicidal, antiplasmodial and cytotoxic activity of indole alkaloids from Corynanthe pachycerasView study →}

Mechanisms

The load-bearing row is the first one: the entire “kratom contains its own opioid antagonist” story is a reading of intermediate intrinsic efficacy, and the adrenergic rows are where the molecule most likely differs from its famous relative — but they are affinities without functions.

Pharmacokinetics

Corynantheidine is the rare minor kratom alkaloid with a dedicated pharmacokinetic study, and the results contradict what in-vitro work predicted.

In human liver microsomes it looked fragile: an in-vitro half-life of 6.1 minutes, the shortest of five kratom alkaloids tested (mitragynine 20 min, speciociliatine 41.8 min, 9-hydroxycorynantheidine 181 min, 7-hydroxymitragynine 170 min), from which the authors predicted poor systemic exposure ^{2Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →}. It is also >97% bound to human plasma protein (unbound fraction 0.02), though the corrected hepatic extraction ratio came out low (E = 0.20) ^{2Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →}.

In live rats it behaved much better. After 2.5 mg/kg intravenous and 20 mg/kg oral dosing, absolute oral bioavailability was 49.9 ± 16.4%, with Cmax 213 ng/mL reached at a slow Tmax of 4.1 h, a mean residence time of 8.8 h orally (3.0 h intravenously), clearance 884 mL/h and an apparent volume of distribution of 8.0 L — i.e. prolonged absorption and extensive extravascular distribution ^{5Reference 5King TI et al. · 2020Bioanalytical method development and validation of corynantheidine, a kratom alkaloid, using UPLC-MS/MS, and its application to preclinical pharmacokinetic studiesView study →}. Imaging mass spectrometry detected the compound in brain tissue, in the corpus callosum and parts of the hippocampus, confirming central penetration ^{5Reference 5King TI et al. · 2020Bioanalytical method development and validation of corynantheidine, a kratom alkaloid, using UPLC-MS/MS, and its application to preclinical pharmacokinetic studiesView study →}.

Most tellingly, when eleven kratom alkaloids were tracked after an oral dose of whole kratom tea or a commercial liquid product, only four — mitragynine, 7-hydroxymitragynine, speciociliatine and corynantheidine — still showed systemic exposure at eight hours; paynantheine and speciogynine fell below quantification within an hour ^{6Reference 6Kamble SH et al. · 2021AnimalPharmacokinetics of eleven kratom alkaloids following an oral dose of either traditional or commercial kratom products in ratsView study →}. Dose-normalised exposure to all four was 1.6–2.4-fold higher from the commercial concentrate than from traditional tea ^{6Reference 6Kamble SH et al. · 2021AnimalPharmacokinetics of eleven kratom alkaloids following an oral dose of either traditional or commercial kratom products in ratsView study →}. For a molecule present at a fraction of a percent, that persistence is the strongest argument that it is worth characterising.

Clinical Trials

None. There is no clinical trial, no human pharmacokinetic study, and no human safety data for isolated corynantheidine. Human exposure occurs only as a minor component of kratom products, where it has never been isolated as a variable.

Last checked: July 2026.

Isolate vs. Plant Studies

Unusually, every pharmacology result here is the isolate — and that is a problem rather than a strength, because the isolate has never been connected back to the plant.

The 2021 characterisation could not even source the alkaloid from leaf: the authors failed to detect corynantheidine in their reference kratom powder and semi-synthesised it from mitragynine (Lewis-acid demethylation to 9-hydroxymitragynine, triflation, then palladium-catalysed reduction) ^{1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →}. The 2020 adrenergic panel used material purified from leaf, but again as a pure compound ^{2Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →}. So the molecule has been studied as a chemical, never as a plant constituent in context.

The consequence is that the headline story — whole-leaf kratom contains an alkaloid that opposes its own main actives — is plausible but unmeasured. Nothing in the literature establishes that corynantheidine reaches mu-relevant concentrations from a normal leaf preparation, or that its presence changes what mitragynine does. What the data do support is a weaker claim: the alkaloid survives oral dosing and reaches the brain ^{5,6Reference 5King TI et al. · 2020Bioanalytical method development and validation of corynantheidine, a kratom alkaloid, using UPLC-MS/MS, and its application to preclinical pharmacokinetic studiesView study →Reference 6Kamble SH et al. · 2021AnimalPharmacokinetics of eleven kratom alkaloids following an oral dose of either traditional or commercial kratom products in ratsView study →}, so a contribution is at least mechanically possible. Kratom’s whole-leaf pharmacology is genuinely not the sum of its parts ^{15,17Reference 15Takayama H · 2004Chemistry and pharmacology of analgesic indole alkaloids from the rubiaceous plant, Mitragyna speciosaView study →Reference 17Kruegel AC et al. · 2016Synthetic and receptor signaling explorations of the Mitragyna alkaloids: mitragynine as an atypical molecular framework for opioid receptor modulatorsView study →}, but corynantheidine’s share of that discrepancy is unquantified, and the 2021 authors judged the minor alkaloids collectively “unlikely to play the majority role” ^{1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →}.

Its Role in Plants

Corynantheidine is not a metabolic dead end in kratom — it is a precursor on the way to mitragynine.

All the plant’s monoterpene indole alkaloids descend from strictosidine, the universal precursor formed from tryptamine and secologanin. Engineered yeast work has reconstituted this pathway from scratch: strains producing strictosidine de novo, given the downstream enzymes, yielded corynantheidine at ~1 mg/L, described explicitly as “the precursor to mitragynine” ^{11Reference 11Dror MJ et al. · 2024Engineered biosynthesis of plant heteroyohimbine and corynantheine alkaloids in Saccharomyces cerevisiaeView study →}. Mitragynine is then reached by hydroxylation and O-methylation at C9 — the very step whose absence defines corynantheidine.

The plant’s own chemistry matches that ordering. Across cultivars and tissues, juvenile kratom leaves accumulate more corynantheidine (and speciociliatine) while mature leaves accumulate mitragynine, and corynantheidine shows a clear inverse relationship with mitragynine through leaf development ^{9Reference 9Laforest LC et al. · 2023Metabolite and molecular characterization of Mitragyna speciosa identifies developmental and genotypic effects on monoterpene indole and oxindole alkaloid compositionView study →}. A survey of eight Thai accessions found the same pattern and sharpened it: strictosidine itself was detectable only in juvenile leaves, which also carried significantly higher corynantheidine and iso-corynantheidine than mature leaves, where mitragynine reached up to 1.19% w/w ^{10Reference 10Ransden KE et al. · 2026Comparative analysis of monoterpene indole alkaloid composition and genotypic variation in Thai Mitragyna speciosaView study →}. In both studies leaf developmental stage mattered more than genotype, and alkaloids were absent from roots altogether ^{9,10Reference 9Laforest LC et al. · 2023Metabolite and molecular characterization of Mitragyna speciosa identifies developmental and genotypic effects on monoterpene indole and oxindole alkaloid compositionView study →Reference 10Ransden KE et al. · 2026Comparative analysis of monoterpene indole alkaloid composition and genotypic variation in Thai Mitragyna speciosaView study →}.

The practical reading: corynantheidine content is a marker of young leaf. A preparation made from immature foliage is a chemically different product from one made from mature leaf — richer in the precursor, poorer in the endpoint.

Prevalence in Nature

Corynantheidine is a genuinely minor alkaloid, and its level swings by nearly two orders of magnitude with preparation.

Quantified by validated UPLC-MS/MS across kratom materials, it measured 0.02% w/w in lyophilised kratom tea, 0.08% in several commercial leaf powders, 0.88% in a concentrated commercial product, and 1.16% in an alkaloid-rich fraction — against mitragynine at 0.74%, ~5% and 33.6% in the same samples ^{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 →}. It was below detection in a simple ethanolic extract ^{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 →}. Roughly 1% of the alkaloid fraction is a reasonable rule of thumb, but several groups have failed to find it in particular commercial powders at all ^{1,4Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView 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 →}.

Outside kratom, the alkaloid appears in the bark of Corynanthe pachyceras (Rubiaceae, West Africa), the genus that gave it its name, alongside corynantheine, dihydrocorynantheine, alpha-yohimbine and corynanthine ^{19Reference 19Staerk D et al. · 2000Leishmanicidal, antiplasmodial and cytotoxic activity of indole alkaloids from Corynanthe pachycerasView study →} — a reminder that the corynanthe skeleton is shared across the family and connects kratom chemically to yohimbe and to the Uncaria alkaloids such as rhynchophylline and hirsutine.

Its Analytical Role

Corynantheidine has a working life beyond pharmacology: it is one of the marker alkaloids used to fingerprint kratom products.

The validated ten-alkaloid UPLC-MS/MS panel that underpins most modern kratom characterisation includes corynantheidine, and — importantly — resolves it from its C20 epimer isocorynantheidine, one of three diastereomer pairs the method was built to separate ^{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 →}. That separation matters: earlier methods that could not resolve kratom’s diastereomers are suspected of overestimating mitragynine, including in human studies ^{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 →}. Full NMR, HRESIMS and ECD reference data for the corynanthe series were later published to put this identification on a firm footing ^{18Reference 18Flores-Bocanegra L et al. · 2020The chemistry of kratom [Mitragyna speciosa]: updated characterization data and methods to elucidate indole and oxindole alkaloidsView study →}.

Because corynantheidine tracks leaf maturity ^{9,10Reference 9Laforest LC et al. · 2023Metabolite and molecular characterization of Mitragyna speciosa identifies developmental and genotypic effects on monoterpene indole and oxindole alkaloid compositionView study →Reference 10Ransden KE et al. · 2026Comparative analysis of monoterpene indole alkaloid composition and genotypic variation in Thai Mitragyna speciosaView study →} and survives to eight hours in plasma ^{6Reference 6Kamble SH et al. · 2021AnimalPharmacokinetics of eleven kratom alkaloids following an oral dose of either traditional or commercial kratom products in ratsView study →}, it is also a plausible product-provenance and exposure marker — a role no other minor alkaloid fills as well. That application has been proposed rather than validated.

Discovery & Synthesis

The alkaloid’s name predates its association with kratom: it is derived from the West African rubiaceous genus Corynanthe, and the molecule was studied first as a Corynanthe constituent ^{19Reference 19Staerk D et al. · 2000Leishmanicidal, antiplasmodial and cytotoxic activity of indole alkaloids from Corynanthe pachycerasView study →}. Its structure and absolute configuration were settled by Bartlett and colleagues in 1962, in the same stereospecific-degradation study that resolved ajmaline and sarpagine ^{14Reference 14Bartlett MF et al. · 1962Rauwolfia alkaloidsView study →}, and the physical criteria distinguishing the normal, pseudo, allo and epiallo configurations of the corynantheidine-type series were laid down by Trager, Lee and Beckett in 1967 ^{13Reference 13Trager WF et al. · 1967Corynantheidine-type alkaloidsView study →}. The precise date and author of its first isolation are not well documented in the indexed literature.

Its kratom identity arrived later, through the Chiba University programme that mapped Mitragyna speciosa’s 9-methoxy-corynanthe alkaloids and clarified which structural features drive their opioid activity ^{3,15Reference 3Takayama H et al. · 2002Studies on the synthesis and opioid agonistic activities of mitragynine-related indole alkaloids: discovery of opioid agonists structurally different from other opioid ligandsView study →Reference 15Takayama H · 2004Chemistry and pharmacology of analgesic indole alkaloids from the rubiaceous plant, Mitragyna speciosaView study →}.

Preparation today is synthetic or semi-synthetic, not extractive. Because leaf content is low and variable — sometimes zero in a given powder — research groups make it instead. The common route is semi-synthesis from mitragynine: Lewis-acid demethylation to 9-hydroxymitragynine, conversion to the triflate, then palladium-catalysed reductive removal of the triflate, which deletes the C9 oxygen entirely ^{1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →}. In 2024 a catalytic asymmetric platform delivered enantioselective syntheses of (−)-corynantheidine and (−)-corynantheidol along with (+)-corynoxine, (−)-corynoxine B and the first enantioselective total synthesis of (−)-corynantheidine pseudoindoxyl — giving laboratory access to the whole corynantheine family across indole, spiro-oxindole and pseudoindoxyl forms ^{12Reference 12Nam Y et al. · 2024A platform for the synthesis of corynantheine-type corynanthe alkaloidsView study →}. A third route is microbial: engineered Saccharomyces cerevisiae producing strictosidine de novo has been extended to corynantheidine at ~1 mg/L ^{11Reference 11Dror MJ et al. · 2024Engineered biosynthesis of plant heteroyohimbine and corynantheine alkaloids in Saccharomyces cerevisiaeView study →}.

Patents: not yet researched.

Toxicity & Safety

Corynantheidine carries a moderate flag. Not because anything toxic has been demonstrated — no toxicology study of the isolated alkaloid exists — but because of what it is: an opioid-receptor-active, brain-penetrant alkaloid with a documented cytochrome-P450 interaction, occurring in a plant with a real adverse-event and dependence record. The badge reflects the class and the absence of a safety package, not a measured harm.

Safety at a Glance

⚠️ Moderate toxicity

• Opioid-receptor active and brain-penetrant. A mu partial agonist that produces mu-dependent antinociception in mice and is detectable in brain tissue after dosing ^{1,5Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →Reference 5King TI et al. · 2020Bioanalytical method development and validation of corynantheidine, a kratom alkaloid, using UPLC-MS/MS, and its application to preclinical pharmacokinetic studiesView study →}. Whatever its efficacy, it is not an inert plant chemical.
• CYP2D6 inhibition. Competitive inhibition with IC50 4.2 µM and Ki 2.8 µM, comparable to mitragynine — relevant to the many drugs cleared by CYP2D6 ^{7Reference 7Kamble SH et al. · 2020Exploration of cytochrome P450 inhibition mediated drug-drug interaction potential of kratom alkaloidsView study →}.
• No toxicology of any kind. No repeat-dose, genotoxicity, reproductive or organ-toxicity data on the isolate. Adverse-effect experiments were deliberately skipped in the one in-vivo study ^{1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →}. Silence is not safety.
• Kratom’s own safety questions apply. Real-world exposure is only ever as part of kratom, whose dependence, withdrawal and adverse-event profile — and whose legal status — vary widely by jurisdiction.

Full Safety & Interactions Detail

Drug interactions — the one concrete finding. Screened against six cytochrome-P450 isoforms in human liver microsomes, corynantheidine was a potent inhibitor of CYP2D6 (IC50 4.2 µM), inhibiting competitively with Ki = 2.8 µM — closely comparable to mitragynine (IC50 2.2 µM, Ki 1.1 µM) ^{7Reference 7Kamble SH et al. · 2020Exploration of cytochrome P450 inhibition mediated drug-drug interaction potential of kratom alkaloidsView study →}. Both alkaloids were judged capable of producing clinically significant interactions with drugs substantially metabolised by CYP2D6 ^{7Reference 7Kamble SH et al. · 2020Exploration of cytochrome P450 inhibition mediated drug-drug interaction potential of kratom alkaloidsView study →}. Corynantheidine also inhibited CYP3A4/5 in a substrate-dependent way — midazolam hydroxylase activity was inhibited, testosterone 6-beta-hydroxylase activity was not — a pattern that complicates simple extrapolation ^{7Reference 7Kamble SH et al. · 2020Exploration of cytochrome P450 inhibition mediated drug-drug interaction potential of kratom alkaloidsView study →}. It is additionally >97% plasma-protein bound, which in principle raises displacement questions with other highly bound drugs ^{2Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →}.

Opioid-class considerations. As a mu partial agonist it belongs, pharmacologically, to a class where additive effects with other opioids and CNS depressants are the standard concern, and where partial agonists can also precipitate withdrawal in someone dependent on a full agonist — the mechanistic corollary of the antagonist behaviour discussed above. Neither has been tested for this molecule. The one in-vivo study explicitly did not investigate respiratory depression, hyperlocomotion, tolerance or dependence for corynantheidine, reasoning from its structural similarity to mitragynine ^{1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →} — so those columns are blank, not reassuring.

Off-target breadth. Radioligand screening across ~50 CNS receptors found corynantheidine binding eleven non-opioid targets, several tighter than mu — notably alpha-2A (74 nM), NMDA (83 nM), alpha-2C (269 nM), alpha-1A (397 nM), sigma-2 (1,073 nM) and 5-HT1A (1,156 nM) ^{1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →}, plus alpha-1D at 42 nM in a separate panel ^{2Reference 2Obeng S et al. · 2020Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloidsView study →}. None has been characterised functionally. An NMDA-binding, adrenergic-binding, opioid-active molecule with no functional profiling at any of those sites is a compound whose behaviour in a person cannot be predicted from this literature.

Reproductive and developmental data (prose only). None exist for isolated corynantheidine. Decisions about kratom exposure in pregnancy or lactation belong to the herb page, where intake is decided, not to a molecule reference.

Regulatory note. Kratom and its alkaloids are controlled, restricted or banned in many jurisdictions and unregulated in others. This page is scholarly pharmacology and toxicology; it is not a use guide and contains no preparation, extraction or dosing instructions.

Dosage

There is no human dose for corynantheidine, and no dose is offered here. The isolated alkaloid has never been administered to a person in a study, has no established therapeutic use, and this is a pharmacology reference rather than a use guide.

The only quantities in the literature are animal characterisation doses, reported so the pharmacokinetics and receptor findings can be read in context: 2.5 mg/kg intravenous and 20 mg/kg oral in rats for the pharmacokinetic study ^{5Reference 5King TI et al. · 2020Bioanalytical method development and validation of corynantheidine, a kratom alkaloid, using UPLC-MS/MS, and its application to preclinical pharmacokinetic studiesView study →}, and 10–100 nmol intracerebroventricular in mice for the antinociception time-course ^{1Reference 1Chakraborty S et al. · 2021Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratomView study →}. Neither route nor species converts to a human dose, and the intracerebroventricular route in particular bypasses everything that determines real-world exposure.

Human exposure occurs only as an incidental fraction of a kratom product, at roughly 0.02–0.9% w/w of the material depending on preparation ^{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, not a personal recommendation.

References

1. Chakraborty S, et al. (2021). Kratom alkaloids as probes for opioid receptor function: pharmacological characterization of minor indole and oxindole alkaloids from kratom. ACS Chemical Neuroscience. https://pubmed.ncbi.nlm.nih.gov/34213886/
2. Obeng S, et al. (2020). Investigation of the adrenergic and opioid binding affinities, metabolic stability, plasma protein binding properties, and functional effects of selected indole-based kratom alkaloids. Journal of Medicinal Chemistry. https://pubmed.ncbi.nlm.nih.gov/31834797/
3. Takayama H, et al. (2002). Studies on the synthesis and opioid agonistic activities of mitragynine-related indole alkaloids: discovery of opioid agonists structurally different from other opioid ligands. Journal of Medicinal Chemistry. https://pubmed.ncbi.nlm.nih.gov/11960505/
4. Sharma A, et al. (2019). Simultaneous quantification of ten key kratom alkaloids in Mitragyna speciosa leaf extracts and commercial products by ultra-performance liquid chromatography-tandem mass spectrometry. Drug Testing and Analysis. https://pubmed.ncbi.nlm.nih.gov/30997725/
5. King TI, et al. (2020). Bioanalytical method development and validation of corynantheidine, a kratom alkaloid, using UPLC-MS/MS, and its application to preclinical pharmacokinetic studies. Journal of Pharmaceutical and Biomedical Analysis. https://pubmed.ncbi.nlm.nih.gov/31838282/
6. Kamble SH, et al. (2021). Pharmacokinetics of eleven kratom alkaloids following an oral dose of either traditional or commercial kratom products in rats. Journal of Natural Products. https://pubmed.ncbi.nlm.nih.gov/33620222/
7. Kamble SH, et al. (2020). Exploration of cytochrome P450 inhibition mediated drug-drug interaction potential of kratom alkaloids. Toxicology Letters. https://pubmed.ncbi.nlm.nih.gov/31707106/
8. Matsumoto K, et al. (2006). Partial agonistic effect of 9-hydroxycorynantheidine on mu-opioid receptor in the guinea-pig ileum. Life Sciences. https://pubmed.ncbi.nlm.nih.gov/16266723/
9. Laforest LC, et al. (2023). Metabolite and molecular characterization of Mitragyna speciosa identifies developmental and genotypic effects on monoterpene indole and oxindole alkaloid composition. Journal of Natural Products. https://pubmed.ncbi.nlm.nih.gov/36913648/
10. Ransden KE, et al. (2026). Comparative analysis of monoterpene indole alkaloid composition and genotypic variation in Thai Mitragyna speciosa. Frontiers in Plant Science. https://pubmed.ncbi.nlm.nih.gov/42158609/
11. Dror MJ, et al. (2024). Engineered biosynthesis of plant heteroyohimbine and corynantheine alkaloids in Saccharomyces cerevisiae. Journal of Industrial Microbiology and Biotechnology. https://pubmed.ncbi.nlm.nih.gov/38140980/
12. Nam Y, et al. (2024). A platform for the synthesis of corynantheine-type corynanthe alkaloids. Journal of the American Chemical Society. https://pubmed.ncbi.nlm.nih.gov/38153983/
13. Trager WF, Lee CM, Beckett AH (1967). Corynantheidine-type alkaloids. I. Establishment of physical criteria for the normal, pseudo, allo and epiallo configurations by conformational analysis. Tetrahedron. https://pubmed.ncbi.nlm.nih.gov/6037286/
14. Bartlett MF, et al. (1962). Rauwolfia alkaloids. XXXVIII. Stereospecific degradations leading to the absolute configurations and structures of ajmaline, sarpagine and corynantheidine. Journal of the American Chemical Society. https://doi.org/10.1021/ja00863a024
15. Takayama H (2004). Chemistry and pharmacology of analgesic indole alkaloids from the rubiaceous plant, Mitragyna speciosa. Chemical and Pharmaceutical Bulletin. https://pubmed.ncbi.nlm.nih.gov/15304982/
16. Váradi A, et al. (2016). Mitragynine/corynantheidine pseudoindoxyls as opioid analgesics with mu agonism and delta antagonism, which do not recruit beta-arrestin-2. Journal of Medicinal Chemistry. https://pubmed.ncbi.nlm.nih.gov/27556704/
17. Kruegel AC, et al. (2016). Synthetic and receptor signaling explorations of the Mitragyna alkaloids: mitragynine as an atypical molecular framework for opioid receptor modulators. Journal of the American Chemical Society. https://pubmed.ncbi.nlm.nih.gov/27192616/
18. Flores-Bocanegra L, et al. (2020). The chemistry of kratom [Mitragyna speciosa]: updated characterization data and methods to elucidate indole and oxindole alkaloids. Journal of Natural Products. https://pubmed.ncbi.nlm.nih.gov/32597657/
19. Staerk D, et al. (2000). Leishmanicidal, antiplasmodial and cytotoxic activity of indole alkaloids from Corynanthe pachyceras. Planta Medica. https://pubmed.ncbi.nlm.nih.gov/10985079/

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