Scoulerine

Scoulerine at a Glance

Scoulerine, also called discretamine, is an isoquinoline alkaloid of the tetrahydroprotoberberine (THPB) class — the same reduced, brain-penetrant family as canadine and l-tetrahydropalmatine. It occurs as a minor alkaloid in California poppy (Eschscholzia californica), Corydalis and the opium poppy ^{1,10Reference 1Bird DA · 2001Berberine bridge enzyme, converting (S)-reticuline to (S)-scoulerine in benzylisoquinoline alkaloid biosynthesis — plant biochemistryView study →Reference 10Mi G et al. · 2016Animall-Scoulerine attenuates behavioural changes induced by methamphetamine in zebrafish and mice — animal studyView study →}.

Its real significance is biochemical rather than therapeutic. As (S)-scoulerine it is the first committed product of the enzyme that gives the whole protoberberine family its name — the berberine bridge enzyme — and the branch-point from which the plant builds berberine, columbamine, protopine, and the benzophenanthridines chelerythrine and sanguinarine. Nearly every other alkaloid on the California-poppy and goldenseal pages descends from this one molecule.

The honest evidence posture on scoulerine as a drug is thin. There are no human trials. What exists is a preclinical literature in two threads: a fairly substantial body of cancer-cell work showing scoulerine is a microtubule-disrupting antimitotic ^{5,6,7Reference 5Habartová K et al. · 2018In vitroScoulerine affects microtubule structure, inhibits proliferation, arrests cell cycle and thus culminates in the apoptotic death of cancer cells — in vitroView study →Reference 6Moshari M et al. · 2022Computational prediction and experimental validation of the unique molecular mode of action of scoulerine — tubulin bindingView study →Reference 7Li J et al. · 2021In vitroThe phytochemical scoulerine inhibits Aurora kinase activity to induce mitotic and cytokinetic defects — in vitroView study →}, and a smaller set of neuropharmacology and in-silico studies placing it, like its class, on dopamine-linked, mildly sedative targets ^{10,11,12Reference 10Mi G et al. · 2016Animall-Scoulerine attenuates behavioural changes induced by methamphetamine in zebrafish and mice — animal studyView study →Reference 11Kalyniukova A et al. · 2025Comprehensive metabolomic profiling and biological activity analysis of Eschscholzia californica extracts using LC-ESI-QTOF-MS — includes in-silico docking of alkaloids (protopine, boldine, (S)-scoulerine) against insomnia-related DRD4/DRD5/SERT targetsView study →Reference 12Tian J et al. · 2020In vitroScoulerine promotes cell viability reduction and apoptosis by activating ROS-dependent endoplasmic reticulum stress in colorectal cancer cells — in vitroView study →}.

Scoulerine as a Biosynthetic Hub

Scoulerine is best understood not as a finished plant product but as a crossroads. It is the point where benzylisoquinoline alkaloid metabolism commits to the protoberberine skeleton and then fans out into several of the most important alkaloid classes here.

Where it comes from. Benzylisoquinoline alkaloids are built from two molecules of tyrosine and funnel through (S)-reticuline, the branch-point of the entire family. The committed step to the protoberberine skeleton is the formation of (S)-scoulerine by the berberine bridge enzyme (BBE) — a flavin-dependent oxidase that forges the extra carbon–carbon bond (the “berberine bridge”) closing reticuline’s structure into the four-ring protoberberine core ^{1,3Reference 1Bird DA · 2001Berberine bridge enzyme, converting (S)-reticuline to (S)-scoulerine in benzylisoquinoline alkaloid biosynthesis — plant biochemistryView study →Reference 3Schrittwieser JH et al. · 2011Biocatalytic organic synthesis of optically pure (S)-scoulerine and berbine and benzylisoquinoline alkaloids — chemoenzymatic synthesisView study →}. This reaction is so distinctive that chemists have borrowed the isolated enzyme to make optically pure (S)-scoulerine in the lab ^{3Reference 3Schrittwieser JH et al. · 2011Biocatalytic organic synthesis of optically pure (S)-scoulerine and berbine and benzylisoquinoline alkaloids — chemoenzymatic synthesisView study →}.

Where it goes. From scoulerine the pathway splits:

• Toward berberine and columbamine — scoulerine 9-O-methyltransferase methylates (S)-scoulerine to (S)-tetrahydrocolumbamine, the step that channels flux toward columbamine, palmatine, epiberberine and, via canadine, berberine ^{2Reference 2Dubouzet JG et al. · 2005Transient RNA silencing of scoulerine 9-O-methyltransferase expression by double-stranded RNA in Coptis japonica protoplasts — plant biochemistryView study →}.
• Toward the methylenedioxy alkaloids — ring closures on the scoulerine skeleton by CYP719-clan P450 enzymes give the protopine-type (protopine, allocryptopine) and, further on, the benzophenanthridine-type (sanguinarine, chelerythrine) alkaloids, and coptisine.

So the alkaloids that dominate California poppy’s and goldenseal’s chemistry are, structurally, elaborations of scoulerine. Because it is an intermediate, plants rarely let it accumulate — which is exactly why it shows up as a minor alkaloid even in species that make large amounts of its descendants.

The California-poppy context. In Eschscholzia, scoulerine sits within the sedative isoquinoline-alkaloid fraction that gives the herb its calming reputation. The herb’s CNS-depressant effect is attributed principally to (S)-reticuline, a positive allosteric modulator at GABAA receptors, with several of the co-occurring alkaloids contributing ^{8Reference 8Fedurco M et al. · 2015In vitroModulatory effects of Eschscholzia californica alkaloids on recombinant GABAA receptors — in vitroView study →}; scoulerine itself is flagged in in-silico screening as a binder of insomnia-related dopamine-transporter and receptor targets ^{11Reference 11Kalyniukova A et al. · 2025Comprehensive metabolomic profiling and biological activity analysis of Eschscholzia californica extracts using LC-ESI-QTOF-MS — includes in-silico docking of alkaloids (protopine, boldine, (S)-scoulerine) against insomnia-related DRD4/DRD5/SERT targetsView study →}. Chemoenzymatic syntheses describe (S)-scoulerine as having “sedative and muscle-relaxing properties” ^{3Reference 3Schrittwieser JH et al. · 2011Biocatalytic organic synthesis of optically pure (S)-scoulerine and berbine and benzylisoquinoline alkaloids — chemoenzymatic synthesisView study →} — a class-level characterisation, not a demonstrated clinical effect. The load-bearing point: scoulerine is a real member of the sedative alkaloid mix, but the measured GABAergic driver in the plant is reticuline, not scoulerine.

What It's Used For

The evidence is preclinical throughout, and it splits into two unrelated stories: a genuinely developed anticancer / antimitotic literature on the isolated molecule, and a thinner CNS / dopamine-linked thread that connects scoulerine to the behaviour of its tetrahydroprotoberberine class.

Evidence by IndicationStrength of support · Beta

Support is an experimental score — a composite weighted by study type (human > animal > in vitro) and volume, tempered for isolate-vs-plant match. A beta, not a validated metric. Every row here is preclinical; scoulerine has no human evidence.

01Antimitotic / Anticancer (Isolated Compound)Shaky44%Multiple isolate studies: microtubule disruption, G2/M arrest, apoptosis; low-µM IC50; some in-vivo ^{5,6,7,9Reference 5Habartová K et al. · 2018In vitroScoulerine affects microtubule structure, inhibits proliferation, arrests cell cycle and thus culminates in the apoptotic death of cancer cells — in vitroView study →Reference 6Moshari M et al. · 2022Computational prediction and experimental validation of the unique molecular mode of action of scoulerine — tubulin bindingView study →Reference 7Li J et al. · 2021In vitroThe phytochemical scoulerine inhibits Aurora kinase activity to induce mitotic and cytokinetic defects — in vitroView study →Reference 9Qu T et al. · 2024In vitroScoulerine: a natural isoquinoline alkaloid targeting SLC6A3 to treat renal cell carcinoma — in vitro/in vivoView study →}

02CNS & Dopamine-Linked ActivityShaky32%In-vivo anti-addiction model + SLC6A3 target + in-silico dopamine binding ^{9,10,11Reference 9Qu T et al. · 2024In vitroScoulerine: a natural isoquinoline alkaloid targeting SLC6A3 to treat renal cell carcinoma — in vitro/in vivoView study →Reference 10Mi G et al. · 2016Animall-Scoulerine attenuates behavioural changes induced by methamphetamine in zebrafish and mice — animal studyView study →Reference 11Kalyniukova A et al. · 2025Comprehensive metabolomic profiling and biological activity analysis of Eschscholzia californica extracts using LC-ESI-QTOF-MS — includes in-silico docking of alkaloids (protopine, boldine, (S)-scoulerine) against insomnia-related DRD4/DRD5/SERT targetsView study →}

03Sedative / GABAergic (Plant Context)Shaky22%Class characterisation + in-silico; measured GABAA driver in the herb is reticuline, not scoulerine ^{3,8,11Reference 3Schrittwieser JH et al. · 2011Biocatalytic organic synthesis of optically pure (S)-scoulerine and berbine and benzylisoquinoline alkaloids — chemoenzymatic synthesisView study →Reference 8Fedurco M et al. · 2015In vitroModulatory effects of Eschscholzia californica alkaloids on recombinant GABAA receptors — in vitroView study →Reference 11Kalyniukova A et al. · 2025Comprehensive metabolomic profiling and biological activity analysis of Eschscholzia californica extracts using LC-ESI-QTOF-MS — includes in-silico docking of alkaloids (protopine, boldine, (S)-scoulerine) against insomnia-related DRD4/DRD5/SERT targetsView study →}

Mechanisms

The two therapeutic threads may not be independent: the same dopamine-transporter affinity that places scoulerine in its sedative CNS class ^{9,10Reference 9Qu T et al. · 2024In vitroScoulerine: a natural isoquinoline alkaloid targeting SLC6A3 to treat renal cell carcinoma — in vitro/in vivoView study →Reference 10Mi G et al. · 2016Animall-Scoulerine attenuates behavioural changes induced by methamphetamine in zebrafish and mice — animal studyView study →} is the target one anticancer study pins its renal-carcinoma effect on ^{9Reference 9Qu T et al. · 2024In vitroScoulerine: a natural isoquinoline alkaloid targeting SLC6A3 to treat renal cell carcinoma — in vitro/in vivoView study →}.

Pharmacokinetics

Essentially unstudied for scoulerine in humans. No oral bioavailability figure, plasma half-life or metabolite map has been established. One structural inference is worth stating and no more: unlike quaternary berberine (oral bioavailability <1%, gut-confined), scoulerine is a lipophilic tertiary amine, consistent with better membrane penetration and the CNS activity its class shows ^{10Reference 10Mi G et al. · 2016Animall-Scoulerine attenuates behavioural changes induced by methamphetamine in zebrafish and mice — animal studyView study →} — but that is inference from structure and class behaviour, not measured human data. Because scoulerine is a metabolic intermediate, its in-vivo fate would also plausibly include enzymatic conversion toward downstream protoberberine products.

Clinical Trials

None. No registered or published human clinical trials of scoulerine as an isolated agent were identified.

Last checked: July 2026.

Isolate vs. Plant Studies

All of scoulerine’s therapeutic evidence is on the isolated molecule — there is no whole-plant trial that isolates a scoulerine effect. The anticancer work purifies or sources scoulerine and tests it against cell lines and a few mouse models ^{5,6,7,9Reference 5Habartová K et al. · 2018In vitroScoulerine affects microtubule structure, inhibits proliferation, arrests cell cycle and thus culminates in the apoptotic death of cancer cells — in vitroView study →Reference 6Moshari M et al. · 2022Computational prediction and experimental validation of the unique molecular mode of action of scoulerine — tubulin bindingView study →Reference 7Li J et al. · 2021In vitroThe phytochemical scoulerine inhibits Aurora kinase activity to induce mitotic and cytokinetic defects — in vitroView study →Reference 9Qu T et al. · 2024In vitroScoulerine: a natural isoquinoline alkaloid targeting SLC6A3 to treat renal cell carcinoma — in vitro/in vivoView study →}, which is the right design but leaves scoulerine’s activity firmly in the preclinical, single-compound column. The CNS data are likewise isolate-and-animal ^{10Reference 10Mi G et al. · 2016Animall-Scoulerine attenuates behavioural changes induced by methamphetamine in zebrafish and mice — animal studyView study →}. Crucially, scoulerine is a trace, minor alkaloid in the aerial parts that are actually drunk or tinctured as California poppy — the herb’s own effects are carried by more abundant alkaloids (reticuline’s GABAA modulation, the pavines californidine and eschscholtzine) ^{8Reference 8Fedurco M et al. · 2015In vitroModulatory effects of Eschscholzia californica alkaloids on recombinant GABAA receptors — in vitroView study →}. The transferability caveat therefore cuts hard: neither the isolate’s antimitotic cytotoxicity nor its dopamine pharmacology should be read onto an ordinary California-poppy or Corydalis preparation.

Prevalence in Nature

Scoulerine occurs across the Papaveraceae, Fumariaceae and Menispermaceae — the alkaloid-rich families that build protoberberines. It is a minor alkaloid of California poppy aerial parts, a more prominent one in Corydalis rhizomes (the source used in several of the anticancer studies) ^{7Reference 7Li J et al. · 2021In vitroThe phytochemical scoulerine inhibits Aurora kinase activity to induce mitotic and cytokinetic defects — in vitroView study →}, and was first isolated from opium (Papaver somniferum) ^{4Reference 4Brochmann-Hanssen E · 1966The isolation of (−)-scoulerine from opiumView study →}. Because it is a biosynthetic intermediate rather than a stored end-product, it seldom accumulates to high levels: the plant converts most of it onward to berberine, columbamine, the protopine-type (protopine, allocryptopine) and benzophenanthridine (sanguinarine, chelerythrine) alkaloids ^{2Reference 2Dubouzet JG et al. · 2005Transient RNA silencing of scoulerine 9-O-methyltransferase expression by double-stranded RNA in Coptis japonica protoplasts — plant biochemistryView study →}. As with other protoberberines it concentrates in roots, rhizomes and latex rather than leaves. No comprehensive quantitative survey of scoulerine content across sources was located here — the concentration figures that exist for California poppy are for the total isoquinoline-alkaloid fraction (~1.6% of dried aerial parts) and its dominant alkaloids, not for scoulerine specifically ^{8Reference 8Fedurco M et al. · 2015In vitroModulatory effects of Eschscholzia californica alkaloids on recombinant GABAA receptors — in vitroView study →}.

Discovery & Synthesis

The alkaloid is named for the nineteenth-century Scottish naturalist John Scouler. Its (−)-(S)-enantiomer was isolated from opium by Brochmann-Hanssen and Nielsen in 1966, characterised by the chromatographic and spectroscopic methods of the day ^{4Reference 4Brochmann-Hanssen E · 1966The isolation of (−)-scoulerine from opiumView study →}; the molecule had featured in benzylisoquinoline-alkaloid chemistry before then as the recognised protoberberine branch-point. The most distinctive modern route is chemoenzymatic: Schrittwieser and colleagues (2011) used the isolated berberine bridge enzyme to perform the enantioselective oxidative C–C bond formation that closes a benzylisoquinoline precursor into optically pure (S)-scoulerine, then elaborated it into a family of berbine and benzylisoquinoline alkaloids — turning the plant’s own committed step into a preparative tool ^{3Reference 3Schrittwieser JH et al. · 2011Biocatalytic organic synthesis of optically pure (S)-scoulerine and berbine and benzylisoquinoline alkaloids — chemoenzymatic synthesisView study →}. There is no commercial demand for isolated scoulerine; it is prepared in small quantities for research (by extraction from Corydalis/California poppy or by such biocatalytic synthesis) rather than manufactured at scale.

Patents: not yet researched.

Toxicity & Safety

Scoulerine’s safety is essentially unstudied as an isolated compound, and that absence — not any evidence of safety — is the honest headline. Human dietary exposure is small and indirect: it is a trace alkaloid of California-poppy and Corydalis preparations, which is reassuring at the level of ordinary herbal use. But the isolated molecule’s own pharmacology carries a genuine flag. Scoulerine is a microtubule-disrupting antimitotic that arrests cell division and induces apoptosis in the low-micromolar range ^{5,6,7Reference 5Habartová K et al. · 2018In vitroScoulerine affects microtubule structure, inhibits proliferation, arrests cell cycle and thus culminates in the apoptotic death of cancer cells — in vitroView study →Reference 6Moshari M et al. · 2022Computational prediction and experimental validation of the unique molecular mode of action of scoulerine — tubulin bindingView study →Reference 7Li J et al. · 2021In vitroThe phytochemical scoulerine inhibits Aurora kinase activity to induce mitotic and cytokinetic defects — in vitroView study →}; microtubule/spindle poisons are inherently aneugenic (they can mis-segregate chromosomes), so pharmacological doses of the isolate would not be expected to be inert. No isolated-compound genotoxicity, carcinogenicity, reproductive or repeat-dose toxicology was located.

Safety at a Glance

✅ Low / no toxicity

• Minor, indirect dietary exposure. Scoulerine is consumed only as a trace California-poppy / Corydalis alkaloid, not as a stand-alone supplement.
• Antimitotic at pharmacological doses. The isolate disrupts microtubules and blocks cell division (low-µM cytotoxicity) — an aneugenic mechanism shared with chemotherapy spindle poisons; not inert at dose ^{5,6,7Reference 5Habartová K et al. · 2018In vitroScoulerine affects microtubule structure, inhibits proliferation, arrests cell cycle and thus culminates in the apoptotic death of cancer cells — in vitroView study →Reference 6Moshari M et al. · 2022Computational prediction and experimental validation of the unique molecular mode of action of scoulerine — tubulin bindingView study →Reference 7Li J et al. · 2021In vitroThe phytochemical scoulerine inhibits Aurora kinase activity to induce mitotic and cytokinetic defects — in vitroView study →}.
• Safety essentially unstudied. No human data, and no isolated-compound genotoxicity, reproductive or interaction assessment for scoulerine specifically — treat silence as unknown, not safe.

Note on scope: drug-interaction and pregnancy/lactation risk were not assessed for scoulerine here — those decisions belong to the whole-herb California poppy and Corydalis monographs, where intake is actually decided and where the more abundant, better-characterised alkaloids (California poppy’s CYP-inhibiting eschscholtzine/protopine/allocryptopine) drive the verdict.

Dosage

There is no established or studied human dose for scoulerine. It has never been used as a stand-alone medicine. The figures in the pharmacology sections above are research concentrations in cells and animals (e.g. leukaemic-cell IC50s of 2.7–6.5 µM ^{5Reference 5Habartová K et al. · 2018In vitroScoulerine affects microtubule structure, inhibits proliferation, arrests cell cycle and thus culminates in the apoptotic death of cancer cells — in vitroView study →}), not doses given to people. Human exposure occurs only as a minor alkaloid within California-poppy or Corydalis preparations, where the “dose of scoulerine” is whatever trace amount the plant and preparation happen to contain. Any figure here would be a research concentration and is not a personal recommendation.

References

1. Bird DA, Facchini PJ. (2001). Berberine bridge enzyme, converting (S)-reticuline to (S)-scoulerine in benzylisoquinoline alkaloid biosynthesis — plant biochemistry. Planta, 213(6), 888–897. https://pubmed.ncbi.nlm.nih.gov/11722125/
2. Dubouzet JG, Morishige T, Fujii N, An CI, Fukusaki E, Ifuku K, Sato F. (2005). Transient RNA silencing of scoulerine 9-O-methyltransferase expression by double-stranded RNA in Coptis japonica protoplasts — plant biochemistry. Bioscience, Biotechnology, and Biochemistry, 69(1), 63–70. https://pubmed.ncbi.nlm.nih.gov/15665469/
3. Schrittwieser JH, Resch V, Wallner S, Lienhart WD, Sattler JH, Resch J, Macheroux P, Kroutil W. (2011). Biocatalytic organic synthesis of optically pure (S)-scoulerine and berbine and benzylisoquinoline alkaloids — chemoenzymatic synthesis. The Journal of Organic Chemistry, 76(15), 6703–6714. https://pubmed.ncbi.nlm.nih.gov/21739961/
4. Brochmann-Hanssen E, Nielsen B. (1966). The isolation of (−)-scoulerine from opium. Tetrahedron Letters, 7(20), 2261–2263. https://pubmed.ncbi.nlm.nih.gov/5923965/
5. Habartová K, Havelek R, Seifrtová M, Královec K, Cahlíková L, Chlebek J, Cermáková E, Mazánková N, Maríková J, Kuneš J, Nováková L, Řezáčová M. (2018). Scoulerine affects microtubule structure, inhibits proliferation, arrests cell cycle and thus culminates in the apoptotic death of cancer cells — in vitro. Scientific Reports, 8, 4829. https://pubmed.ncbi.nlm.nih.gov/29555944/
6. Moshari M, Wang Q, Michalak M, Klobukowski M, Tuszynski JA. (2022). Computational prediction and experimental validation of the unique molecular mode of action of scoulerine — tubulin binding. Molecules, 27(13), 4143. https://pubmed.ncbi.nlm.nih.gov/35807231/
7. Li J, Yan Z, Li H, Shi Q, Ahire V, Zhang S, Nimishetti N, Yang D, Allen TD, Zhang J. (2021). The phytochemical scoulerine inhibits Aurora kinase activity to induce mitotic and cytokinetic defects — in vitro. Journal of Natural Products, 84(8), 2312–2323. https://pubmed.ncbi.nlm.nih.gov/34406008/
8. Fedurco M, Gregorová J, Šebrlová K, Kantorová J, Peš O, Baur R, Sigel E, Táborská E. (2015). Modulatory effects of Eschscholzia californica alkaloids on recombinant GABAA receptors — in vitro. Biochemistry Research International, 2015, 617620. https://pubmed.ncbi.nlm.nih.gov/26509084/
9. Qu T, Sun Y, Zhao J, Liu N, et al. (2024). Scoulerine: a natural isoquinoline alkaloid targeting SLC6A3 to treat renal cell carcinoma — in vitro/in vivo. Biomedicine & Pharmacotherapy, 180, 117524. https://pubmed.ncbi.nlm.nih.gov/39395255/
10. Mi G, Gao Y, Yan H, Jin X, Ye E, Liu S, Gong Z, Yang H, Yang Z. (2016). l-Scoulerine attenuates behavioural changes induced by methamphetamine in zebrafish and mice — animal study. Behavioural Brain Research, 298(Pt B), 97–104. https://pubmed.ncbi.nlm.nih.gov/26433144/
11. Kalyniukova A, Ahmed S, Ak G, Saka E, Duran T, Abul N, Gulcin I, Senkardes I, Cetiz MV, Zengin G. (2025). Comprehensive metabolomic profiling and biological activity analysis of Eschscholzia californica extracts using LC-ESI-QTOF-MS — includes in-silico docking of alkaloids (protopine, boldine, (S)-scoulerine) against insomnia-related DRD4/DRD5/SERT targets. Food Science & Nutrition. https://pubmed.ncbi.nlm.nih.gov/40909255/
12. Tian J, Mo J, Xu L, Zhang R, Qiao Y, Liu B, Jiang L, Ma S, Shi G. (2020). Scoulerine promotes cell viability reduction and apoptosis by activating ROS-dependent endoplasmic reticulum stress in colorectal cancer cells — in vitro. Chemico-Biological Interactions, 327, 109162. https://pubmed.ncbi.nlm.nih.gov/32590070/
13. Wang F, Zhang Y, Pang R, Shi S, Wang R. (2023). Scoulerine promotes cytotoxicity and attenuates stemness in ovarian cancer by targeting PI3K/AKT/mTOR axis — in vitro/in vivo. Acta Pharmaceutica, 73(3), 475–488. https://pubmed.ncbi.nlm.nih.gov/37708956/

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