Harmine

The coincident occurrence of β-carboline alkaloids and serotonin in Peganum harmala indicates the presence of two very similar, interrelated biosynthetic pathways, which makes it difficult to definitively identify whether free tryptamine or L-tryptophan is the precursor in the biosynthesis of harmine.^[7] However, it is postulated that L-tryptophan is the most likely precursor, with tryptamine existing as an intermediate in the pathway.

The following figure shows the proposed biosynthetic scheme for harmine.^[8] The Shikimate acid pathway yields the aromatic amino acid, L-tryptophan. Decarboxylation of L-tryptophan by aromatic L-amino acid decarboxylase (AADC) produces tryptamine (I), which contains a nucleophilic center at the C-2 carbon of the indole ring due to the adjacent nitrogen atom that enables the participation in a Mannich-type reaction. Rearrangements enable the formation of a Schiff base from tryptamine, which then reacts with pyruvate in II to form a β-carboline carboxylic acid. The β-carboline carboxylic acid subsequently undergoes decarboxylation to produce 1-methyl β-carboline III. Hydroxylation followed by methylation in IV yields harmaline. The order of O-methylation and hydroxylation have been shown to be inconsequential to the formation of the harmaline intermediate.^[7] In the last step V, the oxidation of harmaline is accompanied by the loss of water and effectively generates harmine.

The difficulty distinguishing between L-tryptophan and free tryptamine as the precursor of harmine biosynthesis originates from the presence of the serotonin biosynthetic pathway, which closely resembles that of harmine, yet necessitates the availability of free tryptamine as its precursor.^[7] As such, it is unclear if the decarboxylation of L-tryptophan, or the incorporation of pyruvate into the basic tryptamine structure is the first step of harmine biosynthesis. However, feeding experiments involving the feeding of one of tryptamine to hairy root cultures of P. harmala showed that the feeding of tryptamine yielded a great increase in serotonin levels with little to no effect on β-carboline levels, confirming that tryptamine is the precursor for serotonin, and indicating that it is likely only an intermediate in the biosynthesis of harmine; otherwise, comparable increases in harmine levels would have been observed.^[8]

Harmine is a RIMA, as it reversibly inhibits monoamine oxidase A (MAO-A), but not MAO-B.^[4] Oral or intravenous harmine doses ranging from 30 to 300 mg may cause agitation, bradycardia or tachycardia, blurred vision, hypotension, paresthesias. Serum or plasma harmine concentrations may be measured as a confirmation of diagnosis. The plasma elimination half-life of harmine is on the order of 1–3 hours.^[9]

Medically significant amounts of harmine occur in the plants Syrian rue and Banisteriopsis caapi. These plants also contain notable amounts of harmaline,^[3] which is also a RIMA.^[4] The psychoactive ayahuasca brew is made from B. caapi stem bark usually in combination with dimethyltryptamine (DMT) containing Psychotria viridis leaves. DMT is a psychedelic drug, but it is not orally active unless it is ingested with MAOIs. This makes harmine a vital component of the ayahuasca brew with regard to its ability to induce a psychedelic experience.^[10] Syrian rue or synthetic harmine is sometimes used to substitute B. caapi in the oral use of DMT.^[11]

Harmine is a useful fluorescent pH indicator. As the pH of its local environment increases, the fluorescence emission of harmine decreases. Due to its MAO-A specific binding, carbon-11 labeled harmine can be used in positron emission tomography to study MAO-A dysregulation in several psychiatric and neurologic illnesses.^[12] Harmine was used as an antiparkinsonian medication since the late 1920s until the early 1950s. It was replaced by other medications.^[13]

Harmine is currently the only known drug that induces proliferation (rapid mitosis and subsequent mass growth) of pancreatic alpha (α) and beta (β) cells in adult humans.^[14] These islet sub-cells are normally resistant to growth stimulation in the adult stage of a human's life, as the cell mass plateaus at around age 10 and remains virtually unchanged.

A 2024 Phase 1 clinical trial investigating pharmaceutical-grade harmine hydrochloride in healthy adults found that the maximum tolerated dose (MTD) is approximately 2.7 mg/kg body weight.^[15]

Below this threshold, harmine is generally well-tolerated with minimal adverse effects. Above 2.7 mg/kg, common adverse effects include nausea and vomiting, which typically occur 60-90 minutes after ingestion. Other reported effects include drowsiness, dizziness, and impaired concentration. These effects are generally mild to moderate in severity and resolve within several hours.

No serious adverse cardiovascular effects were observed at any dose tested (up to 500 mg), though rare instances of transient hypotension occurred during episodes of vomiting. Unlike some traditional preparations containing harmine (such as Ayahuasca), pure harmine did not cause diarrhea in study participants.

The study found that adverse effects were more common in participants with lower body weight when given fixed doses, leading the researchers to conclude that 2.7 mg/kg represents a more useful threshold than fixed dosing.

Harmine is found in a wide variety of different organisms, most of which are plants.

Alexander Shulgin lists about thirty different species known to contain harmine, including seven species of butterfly in the family Nymphalidae.^[16]

The harmine-containing plants include tobacco, Peganum harmala, two species of passiflora, and numerous others. Lemon balm (Melissa officinalis) contains harmine.^[17]

In addition to B. caapi, at least three members of the Malpighiaceae contain harmine, including two more Banisteriopsis species and the plant Callaeum antifebrile. Callaway, Brito and Neves (2005) found harmine levels of 0.31–8.43% in B. caapi samples.^[18]

The family Zygophyllaceae, which P. harmala belongs to, contains at least two other harmine-bearing plants: Peganum nigellastrum and Zygophyllum fabago.

J. Fritzsche was the first to isolate and name harmine. He isolated it from the husks of Peganum harmala seeds in 1848. The related harmaline was already isolated and named by Fr. Göbel in 1837 from the same plant.^[19][13] The pharmacology of harmine was not studied in detail until 1895.^[13] The structures of harmine and harmaline were determined in 1927 by Richard Helmuth Fredrick Manske and colleagues.^[20][21]

In 1905, the Colombian naturalist and chemist, Rafael Zerda-Bayón suggested the name telepathine to the then unknown hallucinogenic ingredient in ayahuasca brew.^[3][13] "Telepathine" comes from "telepathy", as Zerda-Bayón believed that ayahuasca induced telepathic visions.^[3][22] In 1923, the Colombian chemist, Guillermo Fischer-Cárdenas was the first to isolate harmine from Banisteriopsis caapi, which is an important herbal component of ayahuasca brew. He called the isolated harmine "telepathine".^[3] This was solely to honor Zerda-Bayón, as Fischer-Cárdenas found that telepathine had only mild non-hallucinogenic effects in humans.^[23] In 1925, Barriga Villalba, professor of chemistry at the University of Bogotá, isolated harmine from B. caapi, but named it "yajéine",^[13] which in some texts is written as "yageine".^[3] In 1927, F. Elger, who was a chemist working at Hoffmann-La Roche, isolated harmine from B. caapi. With the assistance of Professor Robert Robinson in Manchester, Elger showed that harmine (which was already isolated in 1848) was identical with telepathine and yajéine.^[24][13] In 1928, Louis Lewin isolated harmine from B. caapi, and named it "banisterine",^[25] but this supposedly novel compound was soon also shown to be harmine.^[13]

Harmine was first patented by Jialin Wu and others who invented ways to produce new harmine derivatives with enhanced antitumor activity and lower toxicity to human nervous cells.^[26]

Harmala alkaloids are considered Schedule 9 prohibited substances under the Poisons Standard (October 2015).^[27] A Schedule 9 substance is a substance which may be abused or misused, the manufacture, possession, sale or use of which should be prohibited by law except when required for medical or scientific research, or for analytical, teaching or training purposes with approval of Commonwealth and/or State or Territory Health Authorities.^[27]

Exceptions are made when in herbs, or preparations, for therapeutic use such as: (a) containing 0.1 per cent or less of harmala alkaloids; or (b) in divided preparations containing 2 mg or less of harmala alkaloids per recommended daily dose.^[27]

• Harmine entry in TiHKAL • info