Two plants, one drink
Ayahuasca combines two plants: the bark of the vine and the leaf of chacruna. Taken by mouth, the DMT in the leaf does nothing on its own, because the MAO enzyme in digestion breaks it down. The harmine and harmaline in the vine block this enzyme for a time. In 1984 McKenna and colleagues studied this mechanism in eight samples from Peru. This is why ayahuasca can interact dangerously with some medicines.
Source: Dennis J. McKenna, G.H.N. Towers, F. Abbott, “Monoamine oxidase inhibitors in South American hallucinogenic plants: tryptamine and β-carboline constituents of ayahuasca”, Journal of Ethnopharmacology 10, 1984 (McKenna et al., J Ethnopharmacol, 1984). This is a folk record, not a treatment recommendation.
Flour sprinkled on wounds: yarrow