Uses

As a MAO inhibitor, harmine inhibits the breakdown of monoamines by enzymes called monoamine oxidases. Monoamines include neurotransmitters (serotonin, dopamine), hormones (melatonin) and drugs, including many hallucinogens (psilocybin, dimethyltryptamine (DMT), mescaline). By slowing the breakdown of neurotransmitters, MAOIs can help to replenish the body's supply of these chemicals, and many MAOIs are used as antidepressants. Harmine has not been the subject of much clinical research in the treatment of depression, which could be due in part to its restricted legal status in many countries, as well as the existence of synthetic MAOIs with fewer side effects.

P. harmala and B. caapi are both traditionally used for their psychoactive effects. B. caapi has a tradition of use in conjunction with plants containing the drug DMT. Traditionally, B. caapi is consumed as a drink, with or without the DMT-bearing plants (see Ayahuasca). Ordinarily, DMT is not active when taken orally, but users report very different effects when DMT is present in such beverages. Harmine and substances containing it have been used in conjunction with many other drugs by modern experimenters. Many hallucinogens appear to exhibit increased potency when used in this way.

Harmine is also a useful fluorescent pH indicator. As the pH of its local environment increases, the fluorescence emission of harmine decreases.

With the radioisotope carbon-11 harmine is used in positron emission tomography neuroimaging to examine its binding to MAO-A.

Harmine found in root secretions of Oxalis tuberosa has been found to have insecticidal properties.

Anticancer

"Harmine showed cytotoxicity against HL60 and K562 cell lines. This could explain the cytotoxic effect of P. harmala on these cells.

Adverse effects

It is important to note that unlike synthetic pharmaceutical MAOIs such as phenelzine, harmine is reversible and selective meaning it does not have nearly as high a risk for the "cheese syndrome" caused by consuming tyramine-containing foods, which is a risk associated with pharmaceutical MAOIs sometimes (mistakenly) applied to all MAO inhibitors. Harmine, and plants containing significant amounts of harmine and other harmala alkaloids are generally not considered safe treatments for depression within the medical community.

Natural sources

Harmine is found in a wide variety of different organisms, most of which are plants. Shulgins list about thirty different species known to contain harmine, including seven species of butterfly in the Nymphalidae family. The harmine-containing plants listed include tobacco, two species of passion flower/passion fruit, and numerous others.

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.

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