Harmine

Harmine, also known as banisterine or telepathine among other synonyms, is a β-carboline and a harmala alkaloid. It occurs in a number of different plants, most notably Peganum harmala and Banisteriopsis caapi. Harmine reversibly inhibits monoamine oxidase A (MAO-A), an enzyme which breaks down monoamines, making it a reversible inhibitor of monoamine oxidase A (RIMA). Harmine does not inhibit MAO-B.

The biosynthesis of harmine likely begins with L-tryptophan, which is decarboxylated to tryptamine—an intermediate also used in serotonin synthesis—before undergoing a series of reactions to form harmine, with feeding experiments supporting tryptamine’s role as an intermediate rather than a primary precursor. It is essential for enabling the oral activity of DMT in ayahuasca and is also used as a fluorescent pH indicator and in PET imaging to study MAO-A-related brain disorders.

Pharmaceutical-grade harmine hydrochloride is safe and well-tolerated at oral doses below 2.7 mg/kg in healthy adults, with higher doses causing mild to moderate gastrointestinal and neurological side effects and limited psychoactive effects. It is found in various plants—including tobacco, Passiflora species, lemon balm, and several Banisteriopsis species—as well as in some butterflies of the Nymphalidae family. Harmine was first isolated and named by in 1848 from Peganum harmala seeds, later identified in Banisteriopsis caapi under various names, with its structure determined in 1927. Recent patents focus on creating harmine derivatives with reduced toxicity.