The MAOI (Monoamine oxidase inhibitor) alkaloids found in seeds of Peganum harmala (also known as Harmal or Syrian Rue)- harmine, harmaline, and tetrahydroharmine- are collectively known as harmala alkaloids.
The harmala alkaloids are of great interest for their complicated relation to phyto-indole entheogens used in Amazonian shamanism.
The harmala alkaloid harmine - once known as Telepathine and Banisterine - is a naturally occurring beta-carboline alkaloid that is structurally related to harmaline. The Shulgins suggest harmaline is a breakdown product of harmine
Harmine and harmaline are reversible MAOIs. They can stimulate the central nervous system by inhibiting the metabolism of monoamine compounds such as serotonin.
The harmala alkaloids occur in harmal in concentrations of roughly 3%, though tests have documented anywhere from 2-7%, as natural sources tend to vary widely in chemical makeup. Harmala alkaloids are also found in the Banisteriopsis caapi vine, the key plant ingredient in the sacramental beverage Ayahuasca, in concentrations that range between 0.31-8.43% for harmine, 0.03-0.83% for harmaline and 0.05-2.94% for tetrahydroharmine [THH]. Many other psychoactive plants are often added to Ayahuasca to achieve visionary consciousness, including leaves from "Psychotria viridis", a source of DMT, The harmala alkaloids serve to potentiate these brewed compounds by preventing their breakdown in the digestive tract. The harmala alkaloids are also psychoactive on their own if the dosage is sufficient, perhaps due to endogenous sources of DMT in the human brain.
Harmala alkaloids are also found in many other plants, such as tobacco and passion flower.
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 monoamine oxidase A inhibitors, but not monoamine oxidase B inhibitors.
Harmine is a reversible inhibitor of MAO-A (RIMA).
Harmaline is a reversible inhibitor of MAO-A (RIMA).