Harmalol

Harmalol at a Glance

Harmalol is a β-carboline (harmala) alkaloid of Syrian rue (Peganum harmala). Structurally it is the 7-hydroxy, O-demethylated analogue of harmaline — it carries a phenolic hydroxyl group exactly where harmaline carries a methoxy group — and it stands in the same relationship to harmaline that harmol does to harmine. It is also formed inside the body when harmaline is metabolised ^{11Reference 11El Gendy MA et al. · 2012Harmaline and harmalol inhibit the carcinogen-activating enzyme CYP1A1 via transcriptional and posttranslational mechanismsView study →}.

Like its relatives it is a reversible, MAO-A-preferring monoamine-oxidase inhibitor and a small molecule that binds nucleic acids, but it has been studied far less than harmine or harmaline and is almost always a minor constituent rather than a plant’s headline alkaloid ^{16Reference 16Bensalem S et al. · 2014Inhibition of myeloperoxidase activity by the alkaloids of Peganum harmala L. (Zygophyllaceae)View study →}. Its literature is genuinely thinner than that of its methoxy siblings, and it is best understood as a preclinical / mechanistic molecule — there are no human trials of isolated harmalol.

Harmalol vs. Harmaline & Harmine

The one thing worth holding onto about harmalol is the hydroxyl-versus-methoxy relationship that defines the harmala family. All four core alkaloids share the same β-carboline (9H-pyrido[3,4-b]indole) skeleton and a methyl group at C-1; they differ in just two positions — the C-7 substituent (methoxy vs. hydroxyl) and whether the C ring is fully aromatic or dihydro:

Alkaloid	C-7 group	C-ring	Relationship
Harmine	methoxy	aromatic	parent
Harmol	hydroxyl	aromatic	O-demethyl-harmine
Harmaline	methoxy	3,4-dihydro	dihydro-harmine
Harmalol	hydroxyl	3,4-dihydro	O-demethyl-harmaline

This single swap — a free phenolic –OH in place of harmaline’s –OCH₃ — is not cosmetic. It makes harmalol more polar and gives it a different electrochemistry: in a myeloperoxidase study, the methoxy alkaloids harmine and harmaline were strong enzyme inhibitors while harmalol and harmol, distinguished by their lower redox potentials, were markedly weaker ^{16Reference 16Bensalem S et al. · 2014Inhibition of myeloperoxidase activity by the alkaloids of Peganum harmala L. (Zygophyllaceae)View study →}. The same demethylation is what the body does to harmaline, so harmalol is both a plant alkaloid and a human metabolite of its own parent ^{11Reference 11El Gendy MA et al. · 2012Harmaline and harmalol inhibit the carcinogen-activating enzyme CYP1A1 via transcriptional and posttranslational mechanismsView study →}.

What It's Used For

Almost all of harmalol’s pharmacology is in-vitro or animal work, and much of it studies the β-carboline group as a set rather than harmalol alone. The best-developed harmalol-specific thread is its binding to DNA and RNA and the cytotoxicity that follows; the MAO inhibition that defines the family is present but poorly quantified for this particular molecule.

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 scores are low by design; read the per-row basis.

01DNA/RNA Binding & CytotoxicityShaky32%Multiple in-vitro biophysical + cancer-cell studies of the isolate ^{2,3,5,6Reference 2Nafisi S et al. · 2010Beta-carboline alkaloids bind DNAView study →Reference 3Sarkar S et al. · 2016DNA binding and apoptotic induction ability of harmalol in HepG2: Biophysical and biochemical approachesView study →Reference 5Sarkar S et al. · 2014Sequence specific binding of beta carboline alkaloid harmalol with deoxyribonucleotidesView study →Reference 6Bhattacharjee P et al. · 2016Targeting different RNA motifs by beta carboline alkaloid, harmalolView study →}

02Antioxidant & NeuroprotectionShaky26%Mouse MPTP model + in-vitro radical scavenging ^{9,10Reference 9Lee CS et al. · 2000AnimalProtective effect of harmalol and harmaline on MPTP neurotoxicity in the mouse and dopamine-induced damage of brain mitochondria and PC12 cellsView study →Reference 10Moura DJ et al. · 2007Antioxidant properties of beta-carboline alkaloids are related to their antimutagenic and antigenotoxic activitiesView study →}

03MAO-A InhibitionShaky24%Cell/tissue assays, class-level; no isolated potency figure ^{7,8Reference 7Santillo MF et al. · 2014In vitroInhibition of monoamine oxidase (MAO) by β-carbolines and their interactions in live neuronal (PC12) and liver cellsView study →Reference 8Miralles A et al. · 2005AnimalHigh-affinity binding of beta-carbolines to imidazoline I2B receptors and MAO-A in rat tissuesView study →}

04CYP1A1 / AhR ModulationShaky20%In-vitro HepG2 chemoprevention study ^{11Reference 11El Gendy MA et al. · 2012Harmaline and harmalol inhibit the carcinogen-activating enzyme CYP1A1 via transcriptional and posttranslational mechanismsView study →}

05Antimicrobial & AntiprotozoalShaky16%In-vitro P. harmala-alkaloid screens; harmalol weak-to-moderate ^{12,13Reference 12Rivas P et al. · 1999Effects of some beta-carboline alkaloids on intact Trypanosoma cruzi epimastigotesView study →Reference 13Arshad N et al. · 2008Effect of Peganum harmala or its beta-carboline alkaloids on certain antibiotic resistant strains of bacteria and protozoa from poultryView study →}

Mechanisms

The load-bearing contrast is with the methoxy siblings: harmalol shares their mechanisms but is consistently the weaker member — weaker MAO story, weaker DNA/protein binding than harmine, weaker enzyme inhibition than harmaline.

Pharmacokinetics

Dedicated pharmacokinetic data for isolated harmalol are sparse, but two facts are well established. First, harmalol is itself a metabolite: in humans given ayahuasca, the harmala alkaloids are O-demethylated and conjugated, and harmalol (from harmaline) — alongside harmol (from harmine) and tetrahydroharmol — appears abundantly as urinary conjugates, confirming O-demethylation-plus-conjugation as a major clearance route for the methoxy parents ^{11,18Reference 11El Gendy MA et al. · 2012Harmaline and harmalol inhibit the carcinogen-activating enzyme CYP1A1 via transcriptional and posttranslational mechanismsView study →Reference 18Riba J et al. · 2012Metabolism and disposition of N,N-dimethyltryptamine and harmala alkaloids after oral administration of ayahuascaView study →}. Second, harmalol binds human serum albumin reversibly at subdomain IIA/IIIA (van der Waals forces and hydrogen bonding dominating), and the presence of serum protein lowers its measured cytotoxicity — a caveat for interpreting the in-vitro potency figures above ^{14,19Reference 14Ghosh T et al. · 2020In vitroIn vitro relationship between serum protein binding to beta-carboline alkaloidsView study →Reference 19Hemmateenejad B et al. · 2012Combined fluorescence spectroscopy and molecular modeling studies on the interaction between harmalol and human serum albuminView study →}.

Clinical Trials

There are no clinical trials of isolated harmalol. Human exposure is incidental — as a minor alkaloid of Peganum harmala preparations and as an in-vivo metabolite of harmaline — and all of the pharmacology above is preclinical.

Last checked: July 2026.

Isolate vs. Plant Studies

Harmalol splits cleanly. Its biophysical and cytotoxicity work uses the pure isolate — harmalol (often as the hydrochloride) versus defined DNA/RNA sequences and single cancer-cell lines — which is a genuine strength for interpreting mechanism ^{2,3,5,6Reference 2Nafisi S et al. · 2010Beta-carboline alkaloids bind DNAView study →Reference 3Sarkar S et al. · 2016DNA binding and apoptotic induction ability of harmalol in HepG2: Biophysical and biochemical approachesView study →Reference 5Sarkar S et al. · 2014Sequence specific binding of beta carboline alkaloid harmalol with deoxyribonucleotidesView study →Reference 6Bhattacharjee P et al. · 2016Targeting different RNA motifs by beta carboline alkaloid, harmalolView study →}. But its whole-plant relevance is limited: in Peganum harmala screens harmalol is the minor partner to harmine and harmaline, contributing little to the extract’s MAO inhibition, antimicrobial action or myeloperoxidase inhibition ^{13,16Reference 13Arshad N et al. · 2008Effect of Peganum harmala or its beta-carboline alkaloids on certain antibiotic resistant strains of bacteria and protozoa from poultryView study →Reference 16Bensalem S et al. · 2014Inhibition of myeloperoxidase activity by the alkaloids of Peganum harmala L. (Zygophyllaceae)View study →}. No study bridges the two — there is no animal or human work showing that the concentrations at which isolated harmalol acts in vitro are ever reached from plant intake. The molecule is a mechanistic tool far more than a demonstrated plant medicine.

Prevalence in Nature

Harmalol occurs chiefly in Syrian rue (Peganum harmala, Zygophyllaceae), the archetypal harmala-alkaloid plant, where it is a minor β-carboline beside the dominant harmaline (seed content up to ~3.8%) and harmine (~2.9%); harmalol is detected in the seeds and aerial parts at much lower, generally unquantified levels ^{16Reference 16Bensalem S et al. · 2014Inhibition of myeloperoxidase activity by the alkaloids of Peganum harmala L. (Zygophyllaceae)View study →}. It is also reported in passionflower (Passiflora spp.), where the whole harmala/β-carboline group is present only in trace amounts, and among the β-carbolines detectable in tobacco (Nicotiana) ^{20Reference 20Santos LFS et al. · 2022A miniaturized matrix solid-phase dispersion methodology for determination of β-carboline alkaloids in tobacco samplesView study →}.

Distinctively, harmalol is not only plant-derived: it is a mammalian metabolite, generated in the body by O-demethylation of ingested harmaline ^{18Reference 18Riba J et al. · 2012Metabolism and disposition of N,N-dimethyltryptamine and harmala alkaloids after oral administration of ayahuascaView study →}. Its absolute abundance in any source has not been well quantified, so no comparative content chart is offered here — the reliable figures belong to its methoxy siblings, not to harmalol.

Discovery & Synthesis

Harmalol belongs to the classical harmala-alkaloid chemistry worked out on Peganum harmala seeds through the nineteenth and early twentieth centuries — the lineage in which Fritzsche isolated harmaline and harmine (1840s) and Perkin, Robinson and Späth later established the β-carboline structures and syntheses. Within that body of work harmalol was recognised as the O-demethyl (7-hydroxy) congener of harmaline; the precise date and author of its own first isolation are not well documented in the accessible literature, reflecting its status as a minor, secondary alkaloid. Its name follows the family convention (harm- root, from harmala), with the -ol suffix marking the phenolic hydroxyl that distinguishes it from harmaline. Today harmalol is obtained the same two ways as its relatives — extraction from P. harmala or O-demethylation of harmaline — and is supplied as a research chemical (commonly the hydrochloride) rather than manufactured at scale, since it has no commercial therapeutic use.

Patents: not yet researched.

Toxicity & Safety

Harmalol carries a moderate flag, inherited from its β-carboline / MAOI class rather than from a large harmalol-specific safety dataset. As a reversible MAO-A-preferring inhibitor ^{7,8Reference 7Santillo MF et al. · 2014In vitroInhibition of monoamine oxidase (MAO) by β-carbolines and their interactions in live neuronal (PC12) and liver cellsView study →Reference 8Miralles A et al. · 2005AnimalHigh-affinity binding of beta-carbolines to imidazoline I2B receptors and MAO-A in rat tissuesView study →} it shares the family’s core hazard — the potential for serotonin toxicity if combined with serotonergic drugs (SSRIs and other antidepressants, certain opioids, other MAOIs) and for tyramine (“cheese”-reaction) hypertensive responses with MAO inhibition — even though harmalol’s own inhibitory potency is less well defined than that of harmine or harmaline. Its intrinsic activity is also cytotoxic and pro-apoptotic in cell models (DNA binding, ROS, p53/caspase-3), which is the basis of its anticancer interest but equally a general-toxicity signal ^{3,6Reference 3Sarkar S et al. · 2016DNA binding and apoptotic induction ability of harmalol in HepG2: Biophysical and biochemical approachesView study →Reference 6Bhattacharjee P et al. · 2016Targeting different RNA motifs by beta carboline alkaloid, harmalolView study →}. There is no adequate human safety data for the isolated molecule.

Safety at a Glance

⚠️ Moderate toxicity

• Only incidental human exposure. Encountered as a minor Peganum harmala alkaloid and as a metabolite of harmaline — not consumed as an isolated compound.
• MAOI-class interaction risk. As a MAO-A-preferring inhibitor it shares the serotonin-toxicity and tyramine-reaction cautions of the harmala alkaloids; the whole plant is the practical exposure route.
• Intrinsically cytotoxic in vitro. DNA-binding, ROS-generating and pro-apoptotic in cell models — the flip side of its anticancer interest.
• Poorly characterised in isolation. No isolated-harmalol human safety, reproductive-toxicity or repeat-dose data; absence of findings is not evidence of safety.

Dosage

There is no established or recommended dose for harmalol — it is a research molecule, not an isolated therapeutic, and human exposure is only indirect (as a trace Peganum harmala alkaloid or a harmaline metabolite). The only quantities on record are experimental: in-vitro cancer-cell activity at roughly GI50/IC50 ≈ 14 µM ^{3,6Reference 3Sarkar S et al. · 2016DNA binding and apoptotic induction ability of harmalol in HepG2: Biophysical and biochemical approachesView study →Reference 6Bhattacharjee P et al. · 2016Targeting different RNA motifs by beta carboline alkaloid, harmalolView study →} and an animal neuroprotection dose of 48 mg/kg in mice ^{9Reference 9Lee CS et al. · 2000AnimalProtective effect of harmalol and harmaline on MPTP neurotoxicity in the mouse and dopamine-induced damage of brain mitochondria and PC12 cellsView study →}. These are research figures, not a personal recommendation, and no safe human dose can be inferred from them.

References

1. Sarkar S, Bhadra K (2018). Therapeutic Role of Harmalol Targeting Nucleic Acids: Biophysical Perspective and in vitro Cytotoxicity. Mini-Reviews in Medicinal Chemistry. https://pubmed.ncbi.nlm.nih.gov/29231137/
2. Nafisi S, et al. (2010). Beta-carboline alkaloids bind DNA. Journal of Photochemistry and Photobiology B. https://pubmed.ncbi.nlm.nih.gov/20541950/
3. Sarkar S, Bhattacharjee P, Bhadra K (2016). DNA binding and apoptotic induction ability of harmalol in HepG2: Biophysical and biochemical approaches. Chemico-Biological Interactions. https://pubmed.ncbi.nlm.nih.gov/27590872/
4. Tshikhudo PP, et al. (2024). Anticancer Potential of β-Carboline Alkaloids: An Updated Mechanistic Overview. Chemistry & Biodiversity. https://pubmed.ncbi.nlm.nih.gov/38108650/
5. Sarkar S, Pandya P, Bhadra K (2014). Sequence specific binding of beta carboline alkaloid harmalol with deoxyribonucleotides. PLoS One. https://pubmed.ncbi.nlm.nih.gov/25247695/
6. Bhattacharjee P, Sarkar S, Pandya P, Bhadra K (2016). Targeting different RNA motifs by beta carboline alkaloid, harmalol. Journal of Biomolecular Structure & Dynamics. https://pubmed.ncbi.nlm.nih.gov/26629671/
7. Santillo MF, et al. (2014). Inhibition of monoamine oxidase (MAO) by β-carbolines and their interactions in live neuronal (PC12) and liver cells. Toxicology in Vitro. https://pubmed.ncbi.nlm.nih.gov/24373881/
8. Miralles A, et al. (2005). High-affinity binding of beta-carbolines to imidazoline I2B receptors and MAO-A in rat tissues. European Journal of Pharmacology. https://pubmed.ncbi.nlm.nih.gov/16061219/
9. Lee CS, et al. (2000). Protective effect of harmalol and harmaline on MPTP neurotoxicity in the mouse and dopamine-induced damage of brain mitochondria and PC12 cells. Journal of Neurochemistry. https://pubmed.ncbi.nlm.nih.gov/10899927/
10. Moura DJ, et al. (2007). Antioxidant properties of beta-carboline alkaloids are related to their antimutagenic and antigenotoxic activities. Mutagenesis. https://pubmed.ncbi.nlm.nih.gov/17545209/
11. El Gendy MA, et al. (2012). Harmaline and harmalol inhibit the carcinogen-activating enzyme CYP1A1 via transcriptional and posttranslational mechanisms. Food and Chemical Toxicology. https://pubmed.ncbi.nlm.nih.gov/22037238/
12. Rivas P, et al. (1999). Effects of some beta-carboline alkaloids on intact Trypanosoma cruzi epimastigotes. Comparative Biochemistry and Physiology C. https://pubmed.ncbi.nlm.nih.gov/10190025/
13. Arshad N, et al. (2008). Effect of Peganum harmala or its beta-carboline alkaloids on certain antibiotic resistant strains of bacteria and protozoa from poultry. Phytotherapy Research. https://pubmed.ncbi.nlm.nih.gov/18814210/
14. Ghosh T, et al. (2020). In vitro relationship between serum protein binding to beta-carboline alkaloids. Journal of Biomolecular Structure & Dynamics. https://pubmed.ncbi.nlm.nih.gov/30909826/
15. Tedesco P, et al. (2020). Comparative Therapeutic Effects of Natural Compounds Against Saprolegnia spp. and Amyloodinium ocellatum. Frontiers in Veterinary Science. https://pubmed.ncbi.nlm.nih.gov/32154278/
16. Bensalem S, et al. (2014). Inhibition of myeloperoxidase activity by the alkaloids of Peganum harmala L. (Zygophyllaceae). Journal of Ethnopharmacology. https://pubmed.ncbi.nlm.nih.gov/24746482/
17. Shahinas D, et al. (2012). Harmine is a potent antimalarial targeting Hsp90 and synergizes with chloroquine and artemisinin. Antimicrobial Agents and Chemotherapy. https://pubmed.ncbi.nlm.nih.gov/22615284/
18. Riba J, et al. (2012). Metabolism and disposition of N,N-dimethyltryptamine and harmala alkaloids after oral administration of ayahuasca. Drug Testing and Analysis. https://pubmed.ncbi.nlm.nih.gov/22514127/
19. Hemmateenejad B, et al. (2012). Combined fluorescence spectroscopy and molecular modeling studies on the interaction between harmalol and human serum albumin. Journal of Pharmaceutical and Biomedical Analysis. https://pubmed.ncbi.nlm.nih.gov/22560122/
20. Santos LFS, et al. (2022). A miniaturized matrix solid-phase dispersion methodology for determination of β-carboline alkaloids in tobacco samples. Journal of Pharmaceutical and Biomedical Analysis. https://pubmed.ncbi.nlm.nih.gov/35671680/

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