Ayahuasca (yage) is a brew made of Banisteriopsis caapi vine (vine of the soul), often in combination with various other plants. It is a natural spiritual medicine used by indigenous people from the Amazonian Peru. Many people who have consumed ayahuasca have spiritual awakenings regarding their purpose on earth, the true nature of the universe and insights into how they can tap into their infinite potential by accessing other dimensions and existences in space-time.
There is an enzyme in your stomach that is in charge of breaking down compounds such as histamine, adrenaline, dopamine, serotonin, melatonin, etc. called the monoamine oxidase enzyme which also breaks down dimethyltryptamine (DMT), when taken orally. Auahuasca is the name of the brew but also that of the vine. There are many different types of brews called ayahuasca simply because it is the fundamental ingredient in all of them. The vine alone, is a strong purgative and has been said to produce visionary states. It contains a family of chemicals called the harmala alkaloids, which are the source of the purge but are also an inhibitor of the monoamine oxidase enzyme, or MAOI.
There are a number of other plants that could potentially be added to the brew from here. Commonly, Chacruna or Wambesa are added as helper plants that contain DMT and increase the intensity of the visions. Mapacho is commonly added. It contains nicotine and harmala alkaloids. Many other plants can be added to the mix, not all being for chemically obvious medicinal purposes. Specific plants can be added by the shaman to treat certain conditions.