Di-Methyl-Tryptamine, commonly referred to as "DMT" is one of the most powerful psychoactive substances known to mankind. Interestingly, this substance is endogenously produced by the human body (and endogenously produced by many other forms of plant and animal life). This characteristic (biosynthesis by humans) is exceptional because it is not shared by any other psychedelic substance.
DMT is also the active hallucinogenic compound in ayahuasca, a tea brewed from the Psychotria viridis shrub and the Banisteriopsis Caapi root. Ayahuasca has used for ritual purposes by indigenous cultures across southern and Central America for hundreds, if not thousands of years.
While Ayahuasca is the oldest known method of DMT consumption, it is now more common for DMT to be consumed in crystal form, by smoking in a pipe, bong, or vaporizer pen. This form of ingestion produces a powerful but short-lasting hallucinogenic state, considered to be one of the most intense psychedelic experiences in existence.
The reason why smoking DMT results in a short experience, while drinking Ayahuasca results in a 12+ hour experience is because of a compound called Monoamine Oxidase (MAO). The human body naturally produces Monoamine Oxidase, and this compound effectively serves to nullify any psychoactive effects that perhaps would be felt due to the bodies naturally produced DMT.
MAO's role in the body is to "clean" neuroreceptors by breaking the bonds that several different monoamine neurotransmitters ( like serotonin, dopamine, and norepinephrine) form with neuroreceptors. N- N, Di-methyl-tryptamine is also a monoamine compound, so therefore endogenously produced DMT is broken down by MAO before it has the chance to bond with neuroreceptors.
When exogenous DMT (not produced by the body) is introduced in large enough amounts (by smoking or vaporizing DMT) it is able to overcome the inhibitory action of MAO and elicit a short but very intense psychedelic experience. The Ayahuasca brew on the other hand contains naturally occurring Monoamine Oxidase Inhibitors (MAOI's), which stop the body from producing MAO. This results in psychoactive effects being felt for a longer period of website time, until the effects of the Monoamine Oxidase Inhibitor wears off.