Ayahuasca is a psychoactive drug that is found in northern South America. It is made from the Banisteriopsis caapi vine and other ingredients. The vine of Banisteriopsis caapi contains monoamine oxidase inhibitors (MAOIs) (hyperlink?) which are alkaloids that are best known for their usage as antidepressants.
Ayahuasca cannot be made from just Banisteriopsis caapi alone - it is combined with other plants that produce dimethyltryptamine (DMT). Plants that contain DMT that are used with Banisteriopsis caapi to make ayahuasca include Psychotria viridis (known as chacruna) or Diplopterys cabrerana (known as chaliponga).
Ayahuasca has traditionally been used for religious and shamanic purposes by indigenous peoples in the Amazon and Peru. Ayahuasca causes individuals to have hallucinations which can be profound and wonderful or frightening depending on the circumstances. Advocates for ayahuasca usage outside of religious ceremonies claim it can have healing and anti-depressant effects if used in a responsible manner.