Banisteriopsis caapi, also known as, caapi, soul vine, or yagé (yage), is a South American liana of the family Malpighiaceae. It is commonly used as an ingredient of ayahuasca, a decoction with a long history of its entheogenic use and its status as a "plant teacher" among the Indigenous peoples of the Amazon rainforest.

Harmala alkaloids are several alkaloids that act as monoamine oxidase inhibitors (MAOIs). These alkaloids are found in the seeds of Peganum harmala, 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 beta-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.