Ayahuasca is a South American psychoactive and entheogenic brewed drink traditionally used both socially and as a ceremonial or shamanic spiritual medicine among the indigenous peoples of the Amazon basin, and more recently in North America and Europe. The tea causes altered states of consciousness often known as "psychedelic experiences" which include visual hallucinations and altered perceptions of reality.

Ayahuasca is commonly made from the Banisteriopsis caapi vine, the Psychotria viridis shrub or a substitute, and other ingredients including Justicia pectoralis, one of the Brugmansia (especially Brugmansia insignis and Brugmansia versicolor, or a hybrid breed) or Datura species, and mapacho (Nicotiana rustica).

A chemically similar preparation, sometimes called "pharmahuasca", can be prepared using N,N-Dimethyltryptamine (DMT) and a pharmaceutical monoamine oxidase inhibitor (MAOI), such as moclobemide or isocarboxazid.

Internationally, the Convention on Psychotropic Substances lists the active ingredient DMT as a schedule 1 drug, but does not control the cultivation of plants from which it can be derived, similarly to the "legal grey area" position of psychedelic plants like peyote and other mescaline-containing cacti.