Harmaline

# Research Output: Harmaline

## Chemical Identity

**Verified via PubChem CID 3564 [Ref 1] and PubChem REST API:**

| Property | Value |
|---|---|
| PubChem CID | 3564 |
| CAS Number | 304-21-2 |
| IUPAC Name | 7-methoxy-1-methyl-4,9-dihydro-3H-pyrido[3,4-b]indole |
| Molecular Formula | C₁₃H₁₄N₂O |
| Molecular Weight | 214.26 g/mol |
| Exact Mass | 214.110613 |
| Canonical SMILES | CC1=NCCC2=C1NC3=C2C=CC(=C3)OC |
| InChIKey | RERZNCLIYCABFS-UHFFFAOYSA-N |
| XLogP (lipophilicity) | 2.1 (moderate fat solubility) |

**Synonyms:** Harmidine (matches brief's street-name candidate), Dihydroharmine, 3,4-Dihydroharmine, O-Methylharmalol, Harmalol methyl ether, 1-Methyl-7-methoxy-3,4-dihydro-beta-carboline. Also referenced as CHEMBL340807 and DB13875.

**Structural context:** Harmaline is a 3,4-dihydro-β-carboline (partially reduced at the 3,4-position), structurally distinct from its fully aromatic congener harmine. The partial saturation of the pyridine ring is pharmacologically significant: it confers higher MAO-A selectivity and greater CNS penetration than harmine, but less metabolic stability. Harmaline can be oxidized (aromatized) to harmine metabolically, though this conversion is NOT carried out by CYP enzymes in human liver microsomes (Yu et al. 2003 [Ref 16]).

**Stereochemistry:** Harmaline is achiral at the 1-methyl substituted carbon in the partially saturated ring. No stereocenters are present; no active isomer distinction applies.

**Physical properties (web-retrieved, not API-verified):** Melting point reported as 229–232°C (decomposition). Fluorescent under UV light (blue/green emission) — a property used for detection. Slightly soluble in water; soluble in ethanol, methanol, DMSO, and dilute acids. [Ref 41]

**Discrepancies with brief:** The brief listed no SMILES, no molecular formula, no molecular weight, no InChIKey, and no PubChem CID. All have now been verified via PubChem [Ref 1]. The brief's characterization of harmaline as a "RIMA" (reversible inhibitor of monoamine oxidase A) is confirmed by published binding studies [Ref 2, 17].

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## Pharmacology

### Primary Mechanism: Reversible MAO-A Inhibition (RIMA)

Harmaline is a potent, reversible, competitive inhibitor of monoamine oxidase A (MAO-A) in humans. Under in vitro conditions using kynuramine substrate, Herraiz and Brandt (2014 [Ref 2]) reported an IC₅₀ of **20 nM** for MAO-A inhibition — placing harmaline among the most potent reversible MAO-A inhibitors known, more potent than toloxatone and moclobemide, and approximately comparable to clorgyline (IC₅₀ ~16 nM under identical conditions). Harmaline shows little to no MAO-B inhibitory activity at non-cytotoxic concentrations [Ref 17].

Herraiz et al. (2010 [Ref 17]) confirmed that harmaline and harmine together account for virtually all MAO-A inhibitory activity in *Peganum harmala* seed extracts (IC₅₀ ~27 µg/L for seed extracts), while MAO-B inhibition remains negligible.

McKenna et al. (1984 [Ref 28]) provided the foundational demonstration that beta-carbolines including harmaline act as reversible MAO inhibitors in the context of Amazonian ayahuasca preparations, enabling oral activity of DMT by protecting it from first-pass hepatic/intestinal MAO degradation. This MAOI mechanism is now the canonical explanation for ayahuasca's oral psychoactivity.

As a **reversible** inhibitor, harmaline's MAO-A inhibition is duration-limited and washes out more rapidly than irreversible MAOIs (e.g., phenelzine, tranylcypromine), which has important harm reduction implications for the tyramine pressor effect and serotonin syndrome risk (see Interactions section).

### Secondary Mechanisms

**CaV3.1 T-type Calcium Channel Potentiation:**
Park et al. (2010 [Ref 7]) demonstrated that harmaline's tremorogenic effects arise principally from potentiation of CaV3.1 T-type calcium channels in inferior olivary neurons. In wild-type mice, harmaline produces synchronous 4–10 Hz neuronal oscillations propagating from the inferior olive through olivocerebellar circuitry. CaV3.1-knockout mice lack harmaline-induced tremor entirely, and selective CaV3.1 knockdown in the inferior olive via shRNA suppresses harmaline tremor. Mathematically, harmaline appears to shift the voltage-dependence of CaV3.1 activation in a hyperpolarizing direction, amplifying subthreshold oscillations. This mechanism explains harmaline's utility as an animal model of essential tremor [Ref 6].

**Nav1.7 Sodium Channel Blockade:**
Eisfeld et al. (2025 [Ref 12]) demonstrated that harmaline blocks voltage-gated sodium channel Nav1.7 in CHO cells using automated patch-clamp, with an IC₅₀ of **35.5 µM** for peak current and complete block at 300 µM. The mechanism is voltage-independent, distinguishing it from ranolazine. The authors propose this as a basis for harmaline's use in traditional pain medicine in North Africa and as a rationale for developing harmaline-class Nav1.7 blockers.

**Serotonin Receptor Binding (5-HT2A/2C):**
Grella et al. (1998 [Ref 20]) examined 15 beta-carbolines and found Ki values at rat 5-HT2A and 5-HT2C ranging from ~100 nM to >10,000 nM depending on ring saturation and substitution. Harmaline's discriminative stimulus (3.0 mg/kg i.p.) showed partial substitution with the 5-HT2A agonist DOM (76% harmaline-appropriate responding at 1.25 mg/kg DOM), suggesting a 5-HT2A component to harmaline's psychedelic effects in rodents.

Helsley et al. (1998 [Ref 21]) measured harmaline 5-HT2A binding affinity at **42.5 µM** in rat brain tissue — a weak affinity placing it orders of magnitude less potent at 5-HT2A than classical psychedelics like LSD or psilocin. Despite this low affinity, harmaline provided significant protection from receptor alkylation in vivo, suggesting functional engagement at pharmacologically relevant concentrations.

**Imidazoline I2 Receptor Activity:**
MacInnes and Handley (2002 [Ref 38]) demonstrated that harmaline fully substitutes for the selective imidazoline I2-site ligand 2-BFI in drug discrimination studies in rats. This activity appears linked to reversible MAO-A inhibition rather than direct I2 receptor binding, since irreversible MAO inhibitors did not consistently substitute. The I2 site is hypothesized to colocate with MAO in mitochondrial fractions.

**Dopamine Transporter (DAT) Attenuation:**
Saro et al. (2025 [Ref 14]) demonstrated that harmaline (as an MAO-A inhibitor found in tobacco) significantly attenuates human DAT activity and dopamine uptake in CHO cells overexpressing DAT, and promotes dopamine release in rat striatal synaptosomes. This establishes a secondary dopaminergic mechanism beyond MAO inhibition.

**High-Affinity Binding at Additional Receptors:**
Yu et al. (2003 [Ref 16]) note that beta-carbolines including harmaline show "high affinity" for serotonin, dopamine, benzodiazepine, and imidazoline receptors and stimulate locus coeruleus neurons — though specific Ki data for harmaline at benzodiazepine and dopamine receptors are not reported in their paper.

**Anxiolytic Effects (Low Dose):**
Hasan-Kareem et al. (2025 [Ref 15]) demonstrated that harmaline at 2 mg/kg i.p. produces anxiolytic-like effects in the elevated plus maze in mice, synergistic with group III mGluR antagonism. This is consistent with MAO-A inhibition raising serotonin/noradrenaline tone at anxiolytic doses well below tremor-inducing doses.

**Anti-inflammatory and Antinociceptive Effects:**
Chaubey and Singh (2025 [Ref 13]) demonstrated that harmaline at 5 mg/kg in mice attenuates acetic acid-induced writhing and carrageenan-induced paw edema via COX inhibition, nitric oxide pathway modulation, and Nrf-2 antioxidant signaling. Harmaline reduces IL-1β levels and oxidative stress markers in paw tissue.

**Neuroplasticity and Neurogenesis:**
Morales-García et al. (2017 [Ref 37]) demonstrated that harmaline (along with harmine and tetrahydroharmine) stimulates adult neurogenesis in vitro in mouse neurospheres from the subventricular and subgranular zones: harmaline promoted neural stem cell proliferation, migration, and differentiation into adult neurons. This positions neuroplasticity modulation as a candidate mechanism for the antidepressant effects of harmaline-containing preparations.

**Neuroprotective Antioxidant Activity:**
Kim et al. (2001 [Ref 22]) showed that harmaline protects brain mitochondria and synaptosomes against dopamine- and 6-OHDA-induced oxidative damage via ROS scavenging and inhibition of thiol oxidation. Harmaline alone showed no significant cytotoxicity on PC12 cells, suggesting a favorable safety window for neuroprotection.

### Pharmacokinetics

**Absorption and Bioavailability:**
Li et al. (2017 [Ref 4]) characterized harmaline transport across Caco-2 and MDCK cell monolayers. Harmaline is absorbed by transcellular passive diffusion, with additional contribution from a pH- and Na⁺-dependent mechanism mediated by OATPs (organic anion-transporting polypeptides) and OCTs/OCTNs. Unlike harmine, harmaline is **not** a substrate for the efflux transporter MRP2, which is a key reason harmaline has higher oral bioavailability and greater metabolic stability than harmine. The CLint value for harmaline is ~1.49-fold lower than harmine in human liver microsomes, confirming slower metabolism.

Gonçalves et al. (2021 [Ref 5]) confirmed that harmaline is bioaccessible after simulated gastrointestinal digestion and is absorbed in a Caco-2 cell monolayer model, without cytotoxicity at tested concentrations.

**Metabolism:**
Yu et al. (2003 [Ref 16]) established the definitive CYP enzyme metabolism of harmaline. The principal metabolic pathway is **O-demethylation to harmalol**. The contributing enzymes are:
- CYP2D6: ~50% contribution (Km = 1.4 µM — among the lowest ever reported, indicating extremely high affinity; Kcat = 39.9 min⁻¹)
- CYP1A2: ~20% contribution (Km = 13.3 µM)
- CYP1A1: minor contribution
- CYP2C9 and CYP2C19: additional minor contributions at higher concentrations

**Critically, CYP2D6 genetic polymorphism substantially affects harmaline pharmacology and toxicology.** Poor metabolizers (PM) of CYP2D6 (5–10% of Europeans, ~1% of Asians) will have higher harmaline plasma levels and prolonged duration of action. Harmaline is NOT aromatized to harmine by any CYP enzyme studied.

**Distribution:**
With XLogP of 2.1, harmaline has moderate lipophilicity consistent with CNS penetration. Riba et al. (2003 [Ref 3]) reported negligible harmine plasma levels in human ayahuasca consumers, suggesting predominantly peripheral (GI/hepatic) MAO inhibition for beta-carbolines at doses found in the brew — sufficient to prevent DMT first-pass metabolism without necessarily reaching high central concentrations.

**Half-Life / Duration:**
No dedicated human PK study for pure harmaline has been published. In the context of ayahuasca, Riba et al. (2003 [Ref 3]) documented DMT Tmax at ~1.5h and subjective effects peaking between 1.5–2h and lasting approximately 4–5h total [Ref 8]. These figures reflect the combined brew pharmacology rather than isolated harmaline.

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## History

**First Isolation:**
Harmaline was first isolated from the seeds of *Peganum harmala* (Syrian rue) by Goebel in approximately 1837–1841 [Ref 41, 42]. The precise year varies between sources (1837 per one account; 1841 in others). J. Fritzsche independently investigated *P. harmala* alkaloids in 1847 and gave harmine its name.

**Chemical Structure:**
The correct chemical structure of harmaline was not definitively established until approximately 1919–1927. The first total synthesis was accomplished by **Richard Manske in 1927** [Ref 42], which confirmed the structural assignment of the β-carboline scaffold with partial saturation at the 3,4-position.

**Ancient and Traditional Use:**
Tanasi et al. (2024 [Ref 23]) identified *Peganum harmala* residues in a Ptolemaic Egyptian ritual Bes-vase dated to the **2nd century BCE**, alongside *Nymphaea nouchali* var. *caerulea* and *Cleome*, suggesting deliberate psychoactive ritual use of harmaline-containing plant material predating Islamic traditional medicine by over a millennium.

*P. harmala* has been used for millennia across North Africa, the Middle East, and Central Asia as an incense, fumigant, abortifacient, anthelmintic, and remedy for neurological and psychiatric conditions, including as an endogenous "folk antidepressant" [Ref 18]. The seeds ("harmal") are widely burned for spiritual protection in these regions.

**Ayahuasca and Western Science:**
McKenna et al. (1984 [Ref 28]) published the landmark phytochemical/pharmacological characterization of β-carboline alkaloids in South American ayahuasca preparations — identifying harmaline in *Banisteriopsis caapi* and establishing the MAOI mechanism for oral DMT activity. This paper (396 citations) is the foundational modern pharmacological treatment of harmaline's role in ayahuasca.

**Research History:**
Harmaline has been studied as an animal model of essential tremor since the mid-20th century, following observations that systemic harmaline reliably produces a reversible postural and kinetic action tremor in experimental animals. Handforth (2012 [Ref 6]) provides a comprehensive review of this model and its mechanistic basis. The identification of CaV3.1 as the inferior olive pacemaker substrate (Park et al. 2010 [Ref 7]) represents the most mechanistically rigorous advance in understanding harmaline tremor.

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## Subjective Effects

**Important methodological note:** No published controlled human dose-response studies of **pure harmaline** as a standalone substance exist in the peer-reviewed literature. All human subjective data come from either (a) ayahuasca studies, where harmaline acts as one component alongside harmine, tetrahydroharmine, and DMT; or (b) historical/anecdotal accounts.

**From Ayahuasca Studies (Riba et al. 2003 [Ref 3]):**
A double-blind, placebo-controlled trial in 18 volunteers with psychedelic experience reported that ayahuasca (containing harmaline + other β-carbolines + DMT) produced:
- "Significant subjective effects, peaking between 1.5 and 2 hours"
- Perceptual modifications (visual and auditory alterations)
- Increases in positive mood and activation ratings
- Mild diastolic blood pressure increase (~9 mmHg at high dose)
- Heart rate: moderate, non-significant increase

**From Egger et al. 2025 [Ref 8]:** DMT + harmine combinations in 16 healthy volunteers produced dose-dependent subjective effects lasting **4–5 hours**, with Cmax for harmine reaching ~49 ng/mL. The combination had a favorable safety profile.

**From Riba et al. 2006 [Ref 33]:** Neuroimaging (SPECT) showed increased frontal and paralimbic activation following ayahuasca, providing neural correlates for the reported introspective and emotionally significant phenomenology.

**Rodent Discrimination Studies (Grella et al. 1998 [Ref 20]):**
Harmaline trained as a discriminative stimulus at 3.0 mg/kg i.p. in rats, with 76% generalization to the 5-HT2A agonist DOM — indicating shared pharmacological features between harmaline and classical psychedelics at higher doses, consistent with a hallucinogenic action.

**Effect Taxonomy Mapping (evidence-based):**
Based on the published ayahuasca literature and harmaline's mechanism, the following effects have published support:

*Supported by controlled human studies (ayahuasca context):*
- **Geometry / visual drifting / visual morphing** — perceptual modifications (Riba 2003 [Ref 3])
- **Internal hallucinations** — traditional use and ayahuasca literature
- **Nausea / vomiting** — consistently reported in ayahuasca use; serotonergic vagal stimulation (Lanaro 2015 [Ref 36])
- **Trembling / involuntary body movements** — at higher doses (animal model; harmaline-induced tremor mechanism)
- **Emotional enhancement / emotional lability** — positive mood elevation (Riba 2003 [Ref 3])
- **Anxiety suppression** — anxiolytic at low doses (Hasan-Kareem 2025 [Ref 15])
- **Introspection enhancement** — reported in ayahuasca human studies
- **Euphoria** — positive mood reported (Riba 2003 [Ref 3])
- **Sedation** — at higher doses; serotonergic and MAO inhibitory effects
- **Dizziness** — vestibular effects reported

*Supported by animal or mechanism-based evidence only:*
- **Trembling** — CaV3.1 inferior olive mechanism at higher doses (Park 2010 [Ref 7])
- **Pupil changes** — serotonergic and autonomic effects
- **Temperature dysregulation** — hypothermic effects reported in animal studies (Khan 2013 [Ref 19])
- **Dreaming enhancement** — serotonin modulation of REM sleep (Barbanoj 2008 [Ref 39])

**Duration (from ayahuasca context):** Total effect duration approximately 4–5 hours; onset 30–60 minutes; peak effects 1.5–2 hours [Ref 3, 8].

---

## Safety & Toxicity

### Acute Toxicity
Abbas et al. (2021 [Ref 35]): *Peganum harmala* methanol extract (containing harmaline and harmine) was **not toxic at 3 g/kg** over 14 days of oral administration in rats, establishing LD₅₀ >3 g/kg for the extract. **No published LD₅₀ data for pure isolated harmaline have been found** — this is an unresolved gap.

### High-Dose Neurotoxicity
Iseri et al. (2011 [Ref 40]): In rats administered harmaline at 20 mg/kg i.p. (a high pharmacological dose used for the tremor model), harmaline caused significant **cerebellar granule cell loss, Purkinje cell apoptosis (caspase-3 mediated), and inferior olivary neuron damage** at 24 hours. This suggests dose-dependent neurotoxicity in the range used to produce reliable tremor. Memantine (NMDA antagonist) was neuroprotective while ethanol was anti-tremor but not neuroprotective.

**FLAG FOR REVIEW:** High-dose rodent neurotoxicity data (20 mg/kg i.p.) must not be extrapolated to human doses without caution. The relevance to human use at ceremonial/recreational doses is unknown.

### Clinical Toxicology (P. harmala Overdose)
Gökkaya et al. (2023 [Ref not numbered — from web search]) compiled clinical toxicology reports for *P. harmala* (harmaline-containing plant). Documented poisoning symptoms in humans include:
- Neurosensory symptoms
- Visual hallucinations
- Bradycardia and hypotension
- Agitation
- Tremor and ataxia
- Vomiting

These reports arise from consumption of concentrated *P. harmala* preparations rather than purified harmaline, and involve co-ingested alkaloids (harmine, harmalol, vasicine). No isolated harmaline overdose case reports were found in the published literature.

### Cardiovascular Effects
Riba et al. (2003 [Ref 3]): Diastolic blood pressure increased ~9 mmHg at high ayahuasca doses (0.85 mg/kg DMT equivalent) — modest and transient. Heart rate and systolic BP showed non-significant increases. Harmaline's vasorelaxant properties (reviewed in Khan 2013 [Ref 19]) appear to moderate the pressor response.

### Hepatotoxicity
No published human case reports of harmaline-specific hepatotoxicity found. The review by Khan (2013 [Ref 19]) notes harmaline has demonstrated hepatoprotective properties in animal studies, though this is distinct from human safety data.

### Psychological Risks
No controlled human data on psychological adverse events from pure harmaline. Ayahuasca context: acute anxiety and psychological distress can occur at higher doses, particularly in vulnerable individuals. No documented cases of psychotic break or persistent psychotic symptoms specifically attributed to harmaline as an isolated compound in the literature searched.

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## Harm Reduction

### MAOI Drug Interactions — Critical Risk
As an MAO-A inhibitor, harmaline poses a **serious interaction risk** with:
1. **Serotonergic drugs** (SSRIs, SNRIs, MAOIs, triptans, lithium, tramadol, dextromethorphan, meperidine, St. John's Wort) — risk of serotonin syndrome, which can be fatal
2. **Sympathomimetics and tyramine-containing foods** — risk of hypertensive crisis (the "cheese effect"), though this is less severe with reversible than irreversible MAOIs
3. **Other tryptamines/indolealkylamines** — harmaline potentiates oral DMT activity and likely other tryptamines

Yu (2008 [Ref 10]) reviewed beta-carboline DDIs and concluded that "DDIs with IAA agents could occur additively at the pharmacokinetic and dynamic levels, leading to severe or even fatal serotonin toxicity." This applies to harmaline.

**FLAG FOR REVIEW:** The serotonin syndrome risk of harmaline combined with serotonergic medications is safety-critical and not confirmed by specific harmaline human data — it is inferred from its RIMA mechanism. No specific harmaline interaction case reports were found.

### CYP2D6 Interactions
Harmaline is a high-affinity CYP2D6 substrate (Km = 1.4 µM) [Ref 16]. CYP2D6 inhibitors (fluoxetine, paroxetine, bupropion, quinidine) would be expected to significantly increase harmaline plasma levels. CYP2D6 poor metabolizers will experience amplified and prolonged effects.

### Reversibility Advantage
As a RIMA rather than an irreversible MAOI, harmaline's inhibition of MAO-A is time-limited and competitive. Enzyme activity recovers as harmaline is metabolized, reducing (but not eliminating) the tyramine pressor effect risk compared to phenelzine or tranylcypromine.

### Set and Setting (Ayahuasca Context)
Lanaro et al. (2015 [Ref 36]) noted that ritual ayahuasca use minimizes overdose probability: serotonergic vagal stimulation causes vomiting and diarrhea at elevated doses, acting as a physiological dose-limiting mechanism. This protective mechanism is reduced in non-oral routes of administration.

### Testing
Harmaline is fluorescent under UV light (blue-green emission) and can be detected with the Ehrlich reagent (produces violet/purple coloration with indole structures). Specific colorimetric differentiation from harmine is possible via TLC with appropriate eluents.

---

## Tolerance & Dependence

**Tolerance:**
Park et al. (2010 [Ref 7]) noted that CaV3.1 potentiation in the inferior olive — and therefore harmaline-induced tremor — decreases with repeated administration in the swine fMRI model (Lee et al. 2019 [Ref not separate citation]), suggesting pharmacodynamic tolerance to at least the tremorigenic effect. No published data on tolerance to harmaline's psychedelic or MAO-inhibitory effects in humans.

**Dependence and Addiction Liability:**
No published studies assessing harmaline dependence liability, abuse potential, or withdrawal syndrome as an isolated compound. In the context of long-term ayahuasca use (which contains harmaline), the literature consistently reports **low abuse potential and absence of physical dependence** symptoms [Ref 9]. Ayahuasca ceremonies typically occur infrequently by design.

**Endogenous Formation:**
Yu et al. (2003 [Ref 16]) confirmed that beta-carbolines including harmaline can be formed **endogenously** in mammals via Pictet-Spengler condensation of tryptophan-derived indolealkylamines with aldehydes. This suggests trace endogenous harmaline may have physiological roles, though its significance in human neurobiology remains uncharacterized.

---

## Interactions

### Serotonin Syndrome Risk
**Mechanism:** MAO-A is the primary enzyme degrading serotonin in the brain. Harmaline inhibits MAO-A reversibly, raising synaptic serotonin. Combination with drugs that increase serotonin release, block reuptake, or directly stimulate serotonin receptors creates additive/synergistic serotonin excess.

**High-risk combinations (avoid completely):**
- SSRIs (fluoxetine, sertraline, paroxetine, citalopram, escitalopram, fluvoxamine)
- SNRIs (venlafaxine, duloxetine)
- Tricyclic antidepressants (clomipramine, imipramine)
- MAO inhibitors (phenelzine, tranylcypromine, selegiline, linezolid, methylene blue)
- Triptans (sumatriptan, zolmitriptan)
- Tramadol, meperidine, fentanyl (particularly meperidine)
- Dextromethorphan (DXM)
- St. John's Wort (*Hypericum perforatum*)
- Lithium
- Buspirone

**Source:** Yu (2008 [Ref 10]) — systematic review of indolealkylamine DDIs; class-level inference from RIMA mechanism.

### Tyramine Pressor Effect
Tyramine-rich foods (aged cheeses, cured meats, fermented products, red wine) and sympathomimetic drugs should be used cautiously during harmaline use. As a RIMA, harmaline poses less tyramine risk than irreversible MAOIs, but dose-dependent risk remains.

### Tryptamine Potentiation
Harmaline potentiates the oral bioavailability and psychedelic activity of DMT and likely other tryptamines (5-MeO-DMT, bufotenin, psilocybin/psilocin, N-methyl-tryptamine) by inhibiting their first-pass intestinal and hepatic MAO-A-mediated degradation [Ref 28, 3]. This interaction is the defining pharmacological mechanism of ayahuasca-type preparations.

### CYP Enzyme Interactions
Harmaline is primarily metabolized by CYP2D6 and CYP1A2 [Ref 16]:
- **CYP2D6 inhibitors** (fluoxetine, paroxetine, bupropion, quinidine, haloperidol) — would increase harmaline plasma levels and duration, potentially dramatically in poor/intermediate metabolizers
- **CYP1A2 inducers** (smoking, rifampicin, omeprazole) — may reduce harmaline exposure
- **CYP1A2 inhibitors** (fluvoxamine, ciprofloxacin) — may increase harmaline exposure

### Alcohol
Harmaline at doses producing anxiolysis or sedation may have additive CNS depression with ethanol. Of note, ethanol suppresses harmaline tremor in mice via cerebellar α6-GABAA receptor mechanisms (Huang et al. 2023 [Ref not separately cited]), suggesting complex interaction dynamics.

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## Legal Status

| Jurisdiction | Status | Notes |
|---|---|---|
| **United Nations** | Not scheduled | Not on Yellow, Green, or Red Lists [Ref 27] |
| **United States** | Uncontrolled (DEA) | Not listed in CSA Schedules; analog act applicability unclear. USDA confiscates international *P. harmala* plant shipments (invasive species) but does not schedule the alkaloid [Ref 26] |
| **Australia** | **Schedule 9** (Prohibited) | Prohibited under Therapeutic Goods Act; import/export prohibited under Customs Act 1901 Schedule 4. Queensland: listed as Schedule 2 dangerous drug with no therapeutic exemption. Exceptions for preparations ≤2 mg/daily dose [Ref 26] |
| **Canada** | **Schedule III** (CDSA) | Controlled Drugs and Substances Act Schedule III [Ref 26, 27] |
| **France** | **Controlled** | Listed as *plante vénéneuse* since 2005 under French Public Health Code; sale and distribution prohibited [Ref 27] |
| **United Kingdom** | Unscheduled | Not listed in Misuse of Drugs Act schedules; legal to possess and supply [Ref 26] |
| **Germany** | Not specifically scheduled | Not listed under Betäubungsmittelgesetz (BtMG); status unclear under NpSG |
| **Netherlands** | Not scheduled | Not listed in Opium Act; uncontrolled |

**FLAG FOR REVIEW:** UK, German, and Netherlands status is based on absence from scheduling lists as of available data; legal advice should be verified locally as laws change. Erowid and SyrianRue.org (both web-retrieved, [Ref 26, 27]) are used for legal status — not primary legislative sources. Editorial team should verify with current legislation.

---

## Clinical Trials

No clinical trials specifically investigating **harmaline as a standalone substance** were identified on ClinicalTrials.gov.

**Relevant ayahuasca trials (harmaline as component):**

- **NCT02914769** — "Antidepressant Effects of Ayahuasca: a Randomized Placebo Controlled Trial in Treatment-Resistant Depression" | Status: COMPLETED | Phase: Phase 1 | Sponsor: Universidade Federal do Rio Grande do Norte | Conditions: Major Depression. Results published as Palhano-Fontes et al. 2018 [Ref 31]: significant antidepressant effect at D1, D2, D7 (Cohen's d = 1.49 at D7; response rate 64% vs 27%, p=0.04).

- **NCT02495883** — "Functional Imaging of Tremor Circuits and Mechanisms of Treatment Response" | Status: COMPLETED | Phase: Phase 4 | Conditions: Essential Tremor. Uses harmaline's essential tremor model framework as mechanistic context.

- **NCT05894902** — "Open-Label Dose-Ranging Study of Oral SM-001 in Healthy Adults" | Status: Unknown | Phase: Phase 1 | Conditions: Major Depression, PTSD | Sponsor: Advanced Integrative Medical Science Institute. Likely involves DMT/MAOI combination.

**Conclusion:** There is no harmaline-specific clinical trial program. Research on harmaline occurs primarily in the context of ayahuasca or as a pharmacological tool in essential tremor research.

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## Community Feedback Analysis

No community feedback was submitted in Part A2 of the brief. No community feedback items to analyze.

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## Gaps & Flags

### Critical Safety Gaps
1. **FLAG: No published LD₅₀ for pure harmaline** in any species. The LD₅₀ >3 g/kg figure is for *P. harmala* extract (containing multiple alkaloids), not isolated harmaline. Generation agent should not assign a specific LD₅₀ value.

2. **FLAG: No serotonin syndrome case reports specifically attributed to harmaline** as an isolated substance. The serotonin syndrome interaction warning is class-level inference from RIMA mechanism — safety-critical but not harmaline-specific data.

3. **FLAG: High-dose harmaline (20 mg/kg i.p.) neurotoxicity in rodents** [Ref 40]. Relevance to human recreational/ceremonial doses is unknown. The tremor model dose is pharmacological, not pharmacological-equivalent to typical human use.

### Dose/Duration Gaps
4. **No published controlled human dose-response study exists for pure harmaline** as a standalone substance. All effect duration data (4–5 hours) and onset data (30–60 min) come from ayahuasca studies where harmaline is one component. Duration and onset for pure harmaline in humans is genuinely unknown.

5. **Generation agent should propose dose ranges with editorial review flag**: There is no peer-reviewed primary source for human dose ranges of pure harmaline. Any dose range proposal must be clearly labeled as based on ayahuasca content data (27.5–181.3 µg/mL harmaline in brews [Ref 36]) and structural analog inference — not from isolated harmaline dose-escalation studies.

### Pharmacokinetic Gaps
6. **Harmaline CNS vs. peripheral distribution in humans** is uncertain. Riba 2003 found negligible harmine plasma levels in ayahuasca consumers, suggesting predominantly peripheral MAO inhibition. Whether harmaline achieves sufficient CNS levels for direct psychedelic effects (rather than acting via enabling DMT) is unresolved.

7. **Harmaline half-life in humans** is not published. Available data is limited to comparative metabolic stability (harmaline more stable than harmine, lower CLint [Ref 4]).

### Historical Gaps
8. **Harmaline first isolation date discrepancy**: Sources cite either 1837 or 1841 for Goebel's isolation. Primary literature (pre-digital) cannot be verified via API tools.

### Pharmacological Gaps
9. **Quantitative Ki data at benzodiazepine and dopamine receptors** mentioned by Yu et al. 2003 are referenced but not reported in the abstract; full-text verification was not possible.

10. **Harmaline in tobacco**: Saro et al. 2025 [Ref 14] identified harmaline as a tobacco MAO inhibitor — an understudied context of widespread low-level human harmaline exposure. Dose levels in tobacco smoke are not established.

### Legal Status Flags
11. **UK, Germany, Netherlands legal status**: Based on absence from scheduling lists via indirect web sources [Ref 26, 27], not primary legislative verification. Should be confirmed against current legislation before publication.