Monoamine oxidase A in the context of Pharmacology of selegiline

Harmala alkaloids are several alkaloids that act as monoamine oxidase inhibitors (MAOIs). These alkaloids are found in the seeds of Peganum harmala (also known as harmal or Syrian rue), as well as Banisteriopsis caapi (ayahuasca), leaves of tobacco and coffee beans.

The alkaloids include harmine, harmaline, harmalol, and their derivatives, which have similar chemical structures, hence the name "harmala alkaloids". These alkaloids are of interest for their use in Amazonian shamanism, where they are derived from other plants. Harmine, once known as telepathine and banisterine, is a naturally occurring β-carboline alkaloid that is structurally related to harmaline, and also found in the vine Banisteriopsis caapi. Tetrahydroharmine is also found in B. caapi and P. harmala. Dr. Alexander Shulgin has suggested that harmine may be a breakdown product of harmaline. Harmine and harmaline are reversible inhibitors of monoamine oxidase A (RIMAs). They can stimulate the central nervous system by inhibiting the metabolism of monoamine compounds such as serotonin and norepinephrine.

Monoamine oxidase inhibitors (MAOIs) are a class of drug that inhibit the activity of one or both monoamine oxidase enzymes: monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B). MAOIs are effective antidepressants due to their specialized function of the inhibition of the enzyme that is responsible for neurotransmitter degradation in the synaptic cleft. This is especially true for treatment-resistant depression, which is a type of depression that is resistant to common treatments of typical depression, such as selective-serotonin reuptake inhibitors (SSRIs) or serotonin-norepinephrine reuptake inhibitors (SNRIs).

MAOIs are also utilized to treat panic disorder, social anxiety disorder, Parkinson's disease, and several other disorders.