Beta-carboline alkaloids harmine, harmaline, and tetrahydroharmine can stimulate the central nervous system by inhibiting the metabolism of amine neurotransmitters, or by direct interaction with specific receptors; they are found in numerous plants, including Peganum harmala, Passiflora incarnata and Banisteriopsis caapi, and in the entheogen preparation Ayahuasca, which is traditionally brewed...