After Spruce’s identification in the 19th century, it was Richard Evans Schultes who did much of the excellent taxonomic detective work in the 1940s and early 1950s. Schultes established that, in addition to Banisteriopsis caapi, ayahuasca tea contained admixture plants. Two of those identified by Schultes, Psychotria viridis (Chacruna) and Diplopterys cabrerana (Chaliponga), were found to contain a potent short-acting hallucinogen: N,N-Dimethyltryptamine, or DMT. As the active alkaloids in the ayahuasca vine—the beta-carbolines harmine, tetrahydroharmine, and harmaline—were known to be only mildly psychoactive on their own, Schultes and his students speculated that ayahuasca’s dramatic effects were the result of a synergistic interaction between the alkaloids in the vine and the DMT in admixture plants. This would prove to be the case.
The beta-carboline alkaloids in ayahuasca were found to be powerful reversible inhibitors of monoamine oxidase, or MAO, an enzyme that normally deactivates DMT. MAO’s being inhibited by beta-carbolines allows DMT to pass the gut, enter the circulatory system, and ultimately cross the blood-brain barrier, where it produces the visions associated with ayahuasca. Unlike his great Victorian predecessor Spruce, Schultes tried ayahuasca many times, though he never allowed such visions as he experienced to carry him to any hyperbolic height. When William Burroughs, a fellow Harvard man, described his ayahuasca visions in florid, apocalyptic terms, Schultes famously replied, “That’s funny, Bill, all I saw was colors.”