# Harmala alkaloid
Harmala alkaloids are a group of β-carboline alkaloids, the best known of which are harmine, harmaline, harmalol, harmol, harmane, and tetrahydroharmine (THH). They occur naturally in plants such as Syrian rue (*Peganum harmala*) and the ayahuasca vine (*Banisteriopsis caapi*), and they act pharmacologically as reversible inhibitors of monoamine oxidase A (MAO-A), the enzyme that breaks down monoamine neurotransmitters in the gut and brain.[1](https://pubmed.ncbi.nlm.nih.gov/20036304/) • [2](https://www.mdpi.com/1420-3049/31/18/3243)
| Key fact | Detail |
|---|---|
| Chemical class | β-carboline (tricyclic indole) alkaloids; main members harmine, harmaline, harmalol, harmol, harmane, tetrahydroharmine[1](https://pubmed.ncbi.nlm.nih.gov/20036304/) |
| First isolation | Harmaline isolated from *Peganum harmala* seeds and roots by Goegel in 1841; harmine from the seeds by Fritsche in 1847[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC13064705/) |
| Signature activity | Reversible MAO-A inhibition; harmine inhibits rat MAO-A with an IC50 of 2–5 nM[4](https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/harmala-alkaloid) |
| Content in Syrian rue | Harmaline about 2.87% and harmine about 2.02% of seed dry weight; harmine 0.69% in roots, with low levels in stems and leaves[5](https://repository.sustech.edu/jspui/bitstream/123456789/17154/1/Antimicrobial%20Activity%20of%20Peganum%20Harmala%20Fixed%20Oil.pdf) |
| Acid-base properties | pKa of harmaline 9.55 ± 0.04 and of harmine 7.45 ± 0.03; comparative pharmacology has been related to these values[6](https://pubmed.ncbi.nlm.nih.gov/6865908/) |
| Oral bioavailability | Harmaline 17.11% versus harmine 1.09% in a comparative study[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC7690791/) |
| Ceremonial dose in ayahuasca | About 1.70 mg/kg harmine, 0.11 mg/kg harmaline, and 1.36 mg/kg THH for a 70 kg person, alongside 1.0 mg/kg DMT[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC11088222/) |
## Chemical identity and occurrence
The harmala alkaloids share a tricyclic β-carboline skeleton built from tryptamine-derived precursors through the [Pictet–Spengler reaction](https://www.edgepedia.org/pictet-spengler-reaction), followed by oxidation and methylation steps that generate the structurally diverse derivatives harmine, harmaline, harmalol, and harmane.[2](https://www.mdpi.com/1420-3049/31/18/3243) Analytical studies of *Peganum harmala* identify harmalol, harmaline, and harmine as the most important constituents of the plant, and harmaline, harmine, harmalol, harmol, and tetrahydroharmine have been identified and quantified as the main β-carboline alkaloids in its extracts.[9](https://pmc.ncbi.nlm.nih.gov/articles/PMC3841998/) • [1](https://pubmed.ncbi.nlm.nih.gov/20036304/)
**Distribution within the plant is uneven.** HPLC analysis of *P. harmala* samples found harmaline abundant only in seeds (2.87%) while harmine was abundant in both seeds (2.02%) and roots (0.69%); stems contained little harmine (0.017%) and no harmaline, and leaves had only trace amounts of both.[5](https://repository.sustech.edu/jspui/bitstream/123456789/17154/1/Antimicrobial%20Activity%20of%20Peganum%20Harmala%20Fixed%20Oil.pdf) The same β-carboline alkaloids also occur in *[Passiflora incarnata](https://www.edgepedia.org/passiflora-incarnata)* and *Banisteriopsis caapi*, the vine used in the Amazonian brew ayahuasca.[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC5566973/)
## Pharmacology
**MAO-A inhibition is the defining activity.** [Harmine](https://www.edgepedia.org/harmine) is a potent inhibitor of monoamine oxidase A, with an IC50 of 2–5 nM in rat tissue, and by blocking MAO-A mediated oxidative deamination of dimethyltryptamine (DMT) in the liver it makes orally ingested DMT active in ayahuasca.[4](https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/harmala-alkaloid) Seed and root extracts of *P. harmala* inhibit MAO-A significantly in vitro with no effect on MAO-B.[9](https://pmc.ncbi.nlm.nih.gov/articles/PMC3841998/)
The alkaloids also act on other targets. Harmaline and harmane modulate voltage-activated calcium channels in vitro in a reversible, use-independent manner,[9](https://pmc.ncbi.nlm.nih.gov/articles/PMC3841998/) and in isolated rabbit aorta and guinea-pig caecum the alkaloids inhibit smooth-muscle contractions through inhibition of different types of Ca2+ channel, with potency varying across the series depending on the structural modification.[11](https://uodiyala.edu.iq/uploads/PDF%20ELIBRARY%20UODIYALA/EL34/Alkaloids%20Chemical%20and%20Biological%20Perspectives.pdf) In one study, three isolated alkaloids (harmine, harmaline, and harmalol) showed an ionotropic effect and decreased heart rate in normal anesthetized dogs.[9](https://pmc.ncbi.nlm.nih.gov/articles/PMC3841998/) β-carboline alkaloids also show strong affinities for enzymes and protein receptor targets including carboxylesterase, MAO-A and MAO-B, cytochrome P450 2E1, and DYRK1A.[4](https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/harmala-alkaloid)
**Harmine itself has a broad activity profile.** Reviews list anti-inflammatory, neuroprotective, antidiabetic, and antitumor activities, along with insecticidal, antiviral, and antibacterial effects; harmine derivatives show similar effects with better antitumor activity and lower neurotoxicity.[12](https://pubmed.ncbi.nlm.nih.gov/33206346) In one mechanistic study, harmine regulated the expression of peroxisome proliferator-activated receptor gamma (PPARγ), the molecular target of thiazolidinedione antidiabetic drugs, through inhibition of the [Wnt signaling pathway](https://www.edgepedia.org/wnt-signaling-pathway).[9](https://pmc.ncbi.nlm.nih.gov/articles/PMC3841998/) Harmine has also been associated with increased levels of brain-derived neurotrophic factor and proliferation of human neural progenitor cells.[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC11088222/)
## Role in ayahuasca
Ayahuasca combines DMT-containing plants such as *Psychotria viridis* with the *Banisteriopsis caapi* vine, whose three main β-carbolines are harmine, harmaline, and tetrahydroharmine.[13](https://www.frontiersin.org/journals/psychiatry/articles/10.3389/fpsyt.2025.1545915/pdf) The β-carbolines prevent enzymatic degradation of DMT in the gut, making DMT orally active, and have psychoactive and therapeutic profiles of their own.[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC11088222/) The average ritual dose of about 100–150 mL for a 70 kg person delivers roughly 1.70 mg/kg harmine, 0.11 mg/kg harmaline, and 1.36 mg/kg THH together with 1.0 mg/kg DMT.[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC11088222/)
The three carbolines differ in their contributions. Harmaline is the most potent psychoactive of the harmala alkaloids, while harmine's psychoactive effects are less prominent; in one study the harmala alkaloids bound 5-HT2 receptors with an affinity similar to DMT.[14](https://pmc.ncbi.nlm.nih.gov/articles/PMC11114307/) Tetrahydroharmine is a weak selective serotonin reuptake inhibitor (SSRI) itself.[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC11088222/) Brewing practices change the balance: religious groups that brew ayahuasca for longer reduce harmaline levels and increase tetrahydroharmine, a reduction product of harmaline, and clinical trials have focused on brews with a higher THH-to-harmaline ratio.[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC11088222/) Syrian rue seeds are also used instead of *B. caapi* in ayahuasca-style preparations.[15](https://dergipark.org.tr/en/download/article-file/2463771)
## Metabolism and drug interactions
The alkaloids are metabolized by cytochrome P450 enzymes. O-demethylation of harmaline and harmine involves polymorphic CYP2D6, suggesting a role for CYP2D6 status in their pharmacology and toxicology, and five β-carbolines from *P. harmala* (harmine, harmaline, harmalol, harmol, and harmane) inhibit CYP3A4 and CYP2D6 in vitro.[16](https://www.sciencedirect.com/science/article/pii/S0022356524362822) • [17](https://pubmed.ncbi.nlm.nih.gov/21433154/) Because of these enzyme effects, β-carbolines may influence the pharmacokinetics of other drugs.[2](https://www.mdpi.com/1420-3049/31/18/3243)
**The main safety concern is herb–drug interaction.** β-carboline alkaloids may potentiate antidepressants, SSRIs, serotonin–norepinephrine reuptake inhibitors, monoamine oxidase inhibitors, sympathomimetic drugs, and other serotonergic medications, increasing the risk of serotonin syndrome or hypertensive crises.[2](https://www.mdpi.com/1420-3049/31/18/3243) Combined use of ayahuasca with drugs such as cannabis and MDMA can also cause meaningful interactions.[18](https://pmc.ncbi.nlm.nih.gov/articles/PMC7678905/)
## Toxicity
The toxicity of *Peganum harmala* is attributed primarily to its β-carboline alkaloids, particularly harmine and harmaline, which are concentrated in the seeds.[2](https://www.mdpi.com/1420-3049/31/18/3243) In a 28-day rat study of a total alkaloid extract of *P. harmala* seeds, the no-observed-adverse-effect level was 45 mg/kg body weight, corresponding to 13.8 mg/kg harmaline and 12.4 mg/kg harmine.[19](https://www.rivm.nl/sites/default/files/2022-03/Beoordeling-Shambala_EN_02032022_1.pdf) High doses of *P. harmala* extract can cause paralysis, liver degeneration, spongiform changes in the central nervous system, euphoria, convulsions, nausea and vomiting, hypothermia, and bradycardia; in mice, intraperitoneal administration of three extracts at 50 mg/kg induced abdominal writhing, body tremors, and decreased locomotor activity, while oral administration showed no toxicity.[9](https://pmc.ncbi.nlm.nih.gov/articles/PMC3841998/) A systematic review of ayahuasca and DMT safety found that isolated harmala alkaloid studies revealed evidence of potential toxicity at higher doses, which may increase with co-administration of certain medications, with harmaline showing the most issues in preclinical models, while serious adverse effects were rarely reported in healthy populations using traditional preparations.[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC11088222/)
## References
1. [beta-Carboline alkaloids in Peganum harmala and inhibition of human monoamine oxidase (MAO), PubMed](https://pubmed.ncbi.nlm.nih.gov/20036304/)
2. [Peganum harmala L.: Essential Oil Composition, Extraction Technologies, Biological Activities and Emerging Applications, Molecules (MDPI)](https://www.mdpi.com/1420-3049/31/18/3243)
3. [Ayahuasca: pharmacology, safety, and therapeutic effects, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC13064705/)
4. [Harmala Alkaloid – an overview, ScienceDirect Topics](https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/harmala-alkaloid)
5. [Antimicrobial Activity of Peganum Harmala Fixed Oil, SUSTech Repository](https://repository.sustech.edu/jspui/bitstream/123456789/17154/1/Antimicrobial%20Activity%20of%20Peganum%20Harmala%20Fixed%20Oil.pdf)
6. [Ionization processes of some harmala alkaloids, PubMed](https://pubmed.ncbi.nlm.nih.gov/6865908/)
7. [Toxicokinetics and Toxicodynamics of Ayahuasca Alkaloids DMT, Harmine, Harmaline and Tetrahydroharmine, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC7690791/)
8. [Ayahuasca and Dimethyltryptamine Adverse Events and Toxicity Analysis: A Systematic Thematic Review, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC11088222/)
9. [Pharmacological and therapeutic effects of Peganum harmala and its main alkaloids, Pharmacognosy Reviews, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC3841998/)
10. [Exposure Characteristics of the Analogous β-Carboline Alkaloids Harmaline and Harmine, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC5566973/)
11. [Alkaloids: Chemical and Biological Perspectives (smooth muscle effects of harmala alkaloids)](https://uodiyala.edu.iq/uploads/PDF%20ELIBRARY%20UODIYALA/EL34/Alkaloids%20Chemical%20and%20Biological%20Perspectives.pdf)
12. [Pharmacological effects of harmine and its derivatives: a review, Arch Pharm Res, PubMed](https://pubmed.ncbi.nlm.nih.gov/33206346)
13. [DMT and harmala alkaloids: an exploratory study of oral Acacia based formulations in healthy volunteers, Frontiers in Psychiatry](https://www.frontiersin.org/journals/psychiatry/articles/10.3389/fpsyt.2025.1545915/pdf)
14. [Ayahuasca: A review of historical, pharmacological, and therapeutic aspects, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC11114307/)
15. [Peganum harmala L. — Review Article, DergiPark](https://dergipark.org.tr/en/download/article-file/2463771)
16. [Contribution of Individual Cytochrome P450 Isozymes to the O-Demethylation of Harmaline and Harmine, ScienceDirect](https://www.sciencedirect.com/science/article/pii/S0022356524362822)
17. [Inhibition of human cytochrome P450 enzymes 3A4 and 2D6 by β-carboline alkaloids, harmine derivatives, PubMed](https://pubmed.ncbi.nlm.nih.gov/21433154/)
18. [The pharmacological interaction of compounds in ayahuasca: a systematic review, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC7678905/)
19. [Assessment of Shambala and a similar herbal preparation, RIVM](https://www.rivm.nl/sites/default/files/2022-03/Beoordeling-Shambala_EN_02032022_1.pdf)
---
*Topic: Encyclopedia › Life and health › Biological foundations › Biochemistry and metabolism › Metabolites, cofactors, and biomolecules › Metabolite records › Drug metabolites*
*Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license