Ayahuasca is a plant concoction from South America ritually used by Amazonian shamans during various rituals and ceremonies. It is prepared by cooking leafs from the Psychotria viridis bush mixed with the liana Banisteriopsis caapi. Nowadays the word is more often associated with a type of spiritual retreat where participants ingest the concoction to improve their mental clarity and well-being. They often reported intense alterations in perception and sensory integration and the induction of a highly altered state of consciousness.
However these studies were not conducted with placebo controls and can be dismissed for the possibility of expectation bias. To more accurately ascertain if the components in ayahuasca produced the reported effects, scientists conducted experiments that measured alkaloid concentrations and interviewed subjects from various age groups along with control groups who were given bogus dosages.
The results were published in Psychopharmacology and be found here: