Harmala alkaloid
The  MAOI (MonAmine 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 monoamines 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 .  
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.

# Telepathine
Telepathine was originally thought to be the active chemical constituent of Banisteriopsis caapi, a key plant ingredient in the preparation of Ayahuasca; a sacremental beverage from the Amazon. This isolated chemical was so named because of the reported effects of Ayahuasca among the indigenous users, including: collective contact with and/or visions of jaguars, snakes, and jeweled birds, and ancestral spirits; the ability to see future events; and as the name suggests, telepathic communication among tribal members.  It was assumed to be a newly discovered chemical at the time, however, it was soon realized that Telepathine was already more widely known as Harmine from its previous discovery in Syrian Rue (Peganum harmala).

# Uses
As mentioned above, some harmala alkaloids can be used as an MAOI (MonoAmine Oxidase Inhibitor) to facilitate the oral ingestion of DMT and other tryptamines; while not generally used as a hallucinogen alone, there are reports of such use.  In high doses, it acts a purgative.  Harmala alkaloids from Banisteriopsis caapi have been used to treat Parkinson's disease.
Additionally, Harmaline is used as a model for Essential Tremor when injected to animals. Rats being treated with Harmaline exhibit severe tremors after 5-7 minutes.
It is important to note that unlike synthetic pharmaceitical 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. Individuals should not attempt to self-medicate themselves for depression using harmine.

# Chemical Forms
- Harmine: C13H12N2O
- Harmaline: C13H14N2O
Harmaline is a "reversible inhibitor of MAO-A (RIMA)."
- Tetrahydroharmine: C13H16N2O
- Harman: C12H10N2
- Harmine acid: methylester:
- Harmilinic acid:
- Harmanamide:
- Acethylnorharnine: