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McKenna would know: He has drunk ayahuasca several hundred times since 1981. An ethnobotanist and ethnopharmacologist by trade, he first tangled with psychedelics as a teen coming of age in the '60s. He tried everything from LSD to jimson weed but never ayahuasca: There was none.
"It was this rare, legendary thing," McKenna remembers.
The first record of ayahuasca arrived in the West in 1908, thanks to the British botanist Richard Spruce, who mostly described lots of vomiting. Harvard ethnobotanist Richard Evan Schultes followed up half a century later with the first academic account. Around the same time, Beat author Burroughs wrote letters depicting his quest for the tea to Ginsberg; those letters were collected in 1963 as The Yage Letters. But in the Western literature, there wasn't much more than that.
Seeking to change that, McKenna embarked on his first trip to South America at age 20. A decade later, he went back, this time to research his dissertation. After months in the jungle, he brought plant samples back to his lab, where he demonstrated for the first time how ayahuasca works.
To make the brew, shamans boil together two Amazonian plants for many hours, sometimes days. As they simmer, the DMT (dimethyltryptamine) contained in one of the plants mixes with the Banisteriopsis vine and its key ingredient: monoamine oxidase inhibitors, or MAOIs. Normally when people ingest DMT — a not-uncommon compound in nature — the monoamine oxidase in our gut knocks it out. But the Banisteriopsis allows the hallucinogen to reach the brain.
By the middle of the 20th century, several Brazilian churches had splintered off from the shamans, taking ayahuasca into a formal setting. In 1991, one of these, União do Vegetal (literally, the Union of the Plants), invited McKenna to one of its twice-monthly ceremonies, during which the tea is administered as a sacrament. (A New Mexico–based branch of the church won a 2006 Supreme Court case allowing it to use ayahuasca in its ceremonies.)
In a room with 500 other people, McKenna drank first one cup, then a second, and was plunged into one of the most vivid ayahuasca visions of his life: a molecule's-eye view of photosynthesis, or, as he explains it, "the force on which life depends."
When McKenna returned to his body, he writes in his new book, The Brotherhood of the Screaming Abyss, "I knew that I had been given an inestimable gift."
McKenna began devising a study to look at the biomedical effects of ayahuasca, and within two years, he was back in Brazil. On this trip, he brought along a team that included Dr. Charles Grob, a psychiatrist and director of the Division of Pediatric and Adolescent Psychiatry at Harbor-UCLA Medical Center.
"Nowadays, the word is out," Grob says. "But when we did this, I'd say, 'We're doing an ayahuasca study,' and people would say, 'aya-what-sca?' "
For about a month in the summer of 1993, the team of the Hoasca Project ran tests on 15 randomly selected members of the União do Vegetal church, all of them men who had been using ayahuasca regularly for at least 10 years. The scientists ran the same tests on their peers who had never been exposed to ayahuasca.
The researchers measured every biological metric they could think of — blood pressure, heart rate, pupil dilation, body temperature — and used structured psychiatric interviews to get where their instruments couldn't: inside the participants' minds.
Many of the men had struggled with alcoholism and depression prior to joining the church, Grob learned. They credited ayahuasca with transforming their outlook. "In some cases," Grob says, "they felt like it had saved their lives."
When the researchers left Brazil and started processing their data, the blood work came back with one of the project's most startling discoveries: The long-term ayahuasca users showed higher levels of the transporters of serotonin, the brain chemical that regulates mood.
Deficits in serotonin transporters are connected with alcoholism and depression — the same problems that the 15 subjects said the ayahuasca had helped cure.
"Here we have a medicine that apparently reverses these deficits, something no other medicine is known to do," McKenna explains. "And there's also a correlation to behavioral change. You can't say it caused it, but there's definitely a correlation."
Today, 20 years after the study, McKenna is preparing to revisit the findings. Within a year, he aims to raise enough money to fund a new study, this time in Peru, to look at the effects of ayahuasca on people with PTSD.
He hopes that additional research will help him reach his ultimate goal: establishing a destination medical clinic in Peru.
"If we can bring together the best of shamanism and the best of psychotherapy, I think we can offer a new paradigm for healing," McKenna says. "What we're really trying to do here is revolutionize psychiatry."