When taken orally, DMT is normally rapidly broken down by the enzyme…

When taken orally, DMT is normally rapidly broken down by the enzyme monoamine oxidase (MAO). This is why traditional ayahuasca brew contains components from two separate plants, one containing DMT, and the other containing MAO inhibitors called harmalas (harmine/harmaline/tetrahydroharmine).

The harmalas are mildly psychoactive on their own, and are as yet unscheduled in the US. In addition to inhibiting the MAO enzyme, they're thought to boost mood, increase calm, and make the DMT trip more likely to be a positive one.

This video explains how and why to use harmalas with DMT.