Harmine drug molecule. Molecular model of Harmine, a hallucinogenic alkaloid found in the seed coats of a plant (Peganum harmala) of the Mediterranean region and the Middle East. It is also found in a South American vine (Banisteriopsis caapi) from which natives of the Andes Mountains prepared a drug for religious and medicinal use. Harmine is a reversibe monoamine oxidase inhibitor (MAOI), meaning it inhibits the breakdown of monoamines such as serotonin, dopamine, melatonin and many hallucinogens (such as DMT). It is also a useful fluorescent pH indicator. Atoms are colour-coded: carbon (grey), hydrogen (white), nitrogen (purple) and oxygen (red).