The day after Apollo 14 landed on the moon, Dennis and Terence McKenna began a trek through the Amazon with four friends who considered themselves, as Terence wrote in his book “True Hallucinations,” “refugees from a society that we thought was poisoned by its own self-hatred and inner contradictions.” They had come to South America, the land of yagé, also known as ayahuasca: an intensely hallucinogenic potion made from boiling woody Banisteriopsis caapi vines with the glossy leaves of the chacruna bush. The brothers, then in their early twenties, were grieving the recent death of their mother, and they were hungry for answers about the mysteries of the cosmos: “We had sorted through the ideological options, and we had decided to put all of our chips on the psychedelic experience.” They started hiking near the border of Peru. As Dennis wrote, in his memoir “The Brotherhood of the Screaming Abyss,” they arrived four days later in La Chorrera, Colombia, “in our long hair, beards, bells, and beads,” accompanied by a “menagerie of sickly dogs, cats, monkeys, and birds” accumulated along the way. (The local Witoto people were cautiously amused.) There, on the banks of the Igara Paraná River, the travellers found themselves in a psychedelic paradise. There were cattle pastures dotted with Psilocybe cubensis—magic mushrooms—sprouting on dung piles; there were hammocks to lounge in while you tripped; there were Banisteriopsis caapi vines growing in the jungle. Taken together, the drugs produced hallucinations that the brothers called “vegetable television.” When they watched it, they felt they were receiving important information directly from the plants of the Amazon. The McKennas were sure they were on to something revelatory, something that would change the course of human history. “I and my companions have been selected to understand and trigger the gestalt wave of understanding that will be the hyperspacial zeitgeist,” Dennis wrote in his journal. Their work was not always easy. During one session, the brothers experienced a flash of mutual telepathy, but then Dennis hurled his glasses and all his clothes into the jungle and, for several days, lost touch with “consensus reality.” It was a small price to pay. The “plant teachers” seemed to have given them “access to a vast database,” Dennis wrote, “the mystical library of all human and cosmic knowledge.” If these sound like the joys and hazards of a bygone era, then you don’t know any ayahuasca users—yet. In the decades since the McKennas’ odyssey, the drug—or “medicine,” as many devotees insist that it be called—has become increasingly popular in the United States, to the point where it’s a “trendy thing right now,” as Marc Maron said recently to Susan Sarandon, on his “WTF” podcast, before they discussed what she’d learned from her latest ayahuasca experience. (“I kind of got, You should just keep your heart open all the time,” she said. “Because the whole point is to be open to the divine in every person in the world.”) The self-help guru Tim Ferriss told me that the drug is everywhere in San Francisco, where he lives. “Ayahuasca is like having a cup of coffee here,” he said. “I have to avoid people at parties because I don’t want to listen to their latest three-hour saga of kaleidoscopic colors.” Leanna Standish, a researcher at the University of Washington School of Medicine, estimated that “on any given night in Manhattan, there are a hundred ayahuasca ‘circles’ going on.” The main psychoactive substance in ayahuasca has been illegal since it was listed in the 1970 Controlled Substances Act, but Standish, who is the medical director of the Bastyr Integrative Oncology Research Center, recently applied for permission from the F.D.A. to do a Phase I clinical trial of the drug—which she believes could be used in treatments for cancer and Parkinson’s disease. “I am very interested in bringing this ancient medicine from the Amazon Basin into the light of science,” Standish said. She is convinced that “it’s going to change the face of Western medicine.” For now, though, she describes ayahuasca use as a “vast, unregulated global experiment.” Most people who take ayahuasca in the United States do so in small “ceremonies,” led by an individual who may call himself a shaman, an ayahuasquero, a curandero, a vegetalista, or just a healer. This person may have come from generations of Shipibo or Quechua shamans in Peru, or he may just be someone with access to ayahuasca. (Under-qualified shamans are referred to as “yogahuascas.”) Ayahuasca was used for centuries by indigenous Amazonians, who believed that it enabled their holy men to treat physical and mental ailments and to receive messages from ancestors and gods. Jesse Jarnow, the author of “Heads: A Biography of Psychedelic America,” told me, “It’s a bit less of a to-do in many of its traditional uses—more about healing specific maladies and illnesses than about addressing spiritual crises.” Now, though, ayahuasca is used as a sacrament in syncretic churches like the Santo Daime and the União do Vegetal (“union of the plant”), both of which have developed a presence in the United States. The entire flock partakes, and the group trip is a kind of congregational service. The first American to study ayahuasca was the Harvard biologist Richard Evans Schultes, who pioneered the field of ethnobotany (and co-authored “Plants of the Gods,” with Albert Hofmann, the Swiss scientist who discovered LSD). In 1976, a graduate student of Schultes’s brought a collection of the plants back from his field research to a greenhouse at the University of Hawaii—where Dennis McKenna happened to be pursuing a master’s degree. Thanks to McKenna, some B. caapi cuttings “escaped captivity,” he told me. “I took them over to the Big Island, where my brother and his wife had purchased some land. They planted it in the forest, and it happened to like the forest—a lot. So now it’s all over the place.” Terence McKenna died in 2000, after becoming a psychedelic folk hero for popularizing magic mushrooms in books, lectures, and instructional cassette tapes. Dennis McKenna went on to get a doctorate in botany and is now a professor at the University of Minnesota. When we spoke, he was on a book tour in Hawaii. He had been hearing about ayahuasca use in a town on the Big Island called Puna, where people call themselves “punatics.” “Everybody is making ayahuasca, taking ayahuasca,” he said. “It’s like the Wild West.”

If cocaine expressed and amplified the speedy, greedy ethos of the nineteen-eighties, ayahuasca reflects our present moment—what we might call the Age of Kale. It is a time characterized by wellness cravings, when many Americans are eager for things like mindfulness, detoxification, and organic produce, and we are willing to suffer for our soulfulness. Ayahuasca, like kale, is no joy ride. The majority of users vomit—or, as they prefer to say, “purge.” And that’s the easy part. “Ayahuasca takes you to the swampland of your soul,” my friend Tony, a photographer in his late fifties, told me. Then he said that he wanted to do it again. “I came home reeking of vomit and sage and looking like I’d come from hell,” Vaughn Bergen, a twenty-seven-year-old who works at an art gallery in Chelsea, said of one ayahuasca trip. “Everyone was trying to talk me out of doing it again. My girlfriend at the time was, like, ‘Is this some kind of sick game?’ I was, like, ‘No. I’m growing.’ ” His next experience was blissful: “I got transported to a higher dimension, where I lived the whole ceremony as my higher self. Anything I thought came to be.” Bergen allows that, of the nine ceremonies he’s attended, eight have been “unpleasant experiences.” But he intends to continue using ayahuasca for the rest of his life. He believes that it will heal not only him but civilization at large. The process of making ayahuasca is beyond artisanal: it is nearly Druidical. “We pick the chacruna leaf at sunrise in this very specific way: you say a prayer and just pick the lower ones from each tree,” a lithe ayahuasquera in her early forties—British accent, long blond hair, a background in Reiki—told me about her harvests, in Hawaii. “You clean the vine with wooden spoons, meticulously, all the mulch away from the roots—they look so beautiful, like a human heart—and you pound these beautiful pieces of vine with wooden mallets until it’s fibre,” she said. “Then it’s this amazing, sophisticated process of one pot here and one pot there, and you’re stirring and you’re singing songs.” She and her boyfriend serve the ayahuasca—“divine consciousness in liquid form”—at ceremonies in New York, Cape Town, Las Vegas, Bali. They showed me pictures of themselves harvesting plants in a verdant Hawaiian jungle, looking radiantly happy. I asked if they made a living this way. “We manifest abundance wherever we go,” she told me. Her boyfriend added, “Consciousness is its own economy.” Like juicing—another Kale Age method of expedient renewal—ayahuasca is appreciated for its efficiency. Enthusiasts often say that each trip is like ten years of therapy or meditation. Ferriss, the author of such “life-hacking” manuals as “The 4-Hour Workweek” and “The 4-Hour Body,” told me, “It’s mind-boggling how much it can do in one or two nights.” He uses ayahuasca regularly, despite a harrowing early trip that he described as “the most painful experience I’ve ever had by a factor of a thousand. I felt like I was being torn apart and killed a thousand times a second for two hours.” This was followed by hours of grand-mal seizures; Ferriss had rug burns on his face the next day. “I thought I had completely fried my motherboard,” he continued. “I remember saying, ‘I will never do this again.’ ” But in the next few months he realized that something astounding had happened to him. “Ninety per cent of the anger I had held on to for decades, since I was a kid, was just gone. Absent.” “Don’t you think it’s time we gave her the back-to-school talk?” Ayahuasca enthusiasts frequently use the language of technology, which may have entered the plant-medicine lexicon because so many people in Silicon Valley are devotees. “Indigenous prophesies point to an imminent polar reversal that will wipe our hard drives clean,” Daniel Pinchbeck wrote in his exploration of ayahuasca, technology, and Mayan millennialism, “2012: The Return of Quetzalcoatl.” In an industry devoted to synthetic products, people are drawn to this natural drug, with its ancient lineage and ritualized use: traditionally, shamans purify the setting by smoking tobacco, playing ceremonial instruments, and chanting icaros—songs that they say come to them from the plants, the way Pentecostals are moved by the Holy Spirit to speak in tongues. “In Silicon Valley, where everyone suffers from neo-mania,” Ferriss continued, “having interactions with songs and rituals that have remained, in some cases, unchanged for hundreds or thousands of years is very appealing.” Ayahuasca isn’t the only time-honored method of ritual self-mortification, of course; pilgrims seeking an encounter with the divine have a long history of fasting, hair shirts, and flagellation. But in the United States most ayahuasca users are seeking a post-religious kind of spiritualism—or, perhaps, pre-religious, a pagan worship of nature. The Scottish writer and ayahuasca devotee Graham Hancock told me that people from all over the world report similar encounters with the “spirit of the plant”: “She sometimes appears as a jungle cat, sometimes as a huge serpent.” Many speak about ayahuasca as though it were an actual female being: Grandmother. “Grandmother may not always give you what you want, but she’ll give you what you need,” an ayahuasquera who calls herself Little Owl said, a few months ago, at an informational meeting in a loft in Chinatown. Two dozen people of diverse ages and ethnicities sat on yoga mats eating a potluck vegetarian meal and watching a blurry documentary about ayahuasca. On the screen, a young man recounted a miserable stomach ailment that no Western doctor could heal. After years of torment, he took ayahuasca during a trip to Peru and visualized himself journeying into his own body and removing a terrifying squid from his intestines. The next day, his pain was gone, and it never came back. After the movie, Little Owl, a fifty-two-year-old of Taiwanese descent with black bangs nearly to her eyebrows, answered questions. “Do your conscious and subconscious work on different frequencies?” a young woman in a tank top wanted to know. “And, if so, which one will Grandmother tap in to?” Little Owl said that Grandmother would address your entire being. A friend of hers, a young African-American man in a knit orange cap who said that he taught mindfulness for a living, was standing by, and Little Owl asked if he had anything to add. “The medicine is like shining a light on whatever conflict needs to be resolved,” he said. A Caucasian guy in his late twenties asked if there was anyone who shouldn’t take the medicine; he was deciding which friends he should bring to the next ceremony. Little Owl, who has a background in acupuncture, replied that every participant would fill out a detailed health form, and that people who have such conditions as high blood pressure or who are on antidepressants should not take ayahuasca. An older man with silver hair and a booming voice spoke next: “Do you have doctors or anyone on hand who understands what’s happening on a pharmacological level if something goes wrong?” There was a tense silence, and then Little Owl replied, “We are healing on a vibrational level.”

A plant is constantly interacting with its ecosystem: attracting insects it needs for pollination, discouraging hungry herbivores, warning other plants that it competes with for nutrients in the soil. It communicates using “messenger molecules,” which allow for semiosis (signalling) and symbiosis (interspecies coöperation), helping the species to improve its circumstances as the process of evolution unfolds. Some of the most important messenger molecules in the plant kingdom are called amines, and are typically derived from amino acids. The human brain, too, is a kind of complex ecosystem, coördinated by messenger molecules of its own: neurotransmitters, which govern everything from the simple mechanism of pupils dilating in dim light to the unfathomable complexity of consciousness. The neurotransmitters that mediate emotion, awareness, and the creation of meaning are amines—such as serotonin, dopamine, and norepinephrine—which evolved from the same molecular antecedents as many plant-messenger molecules. The main psychoactive substance in ayahuasca—N, N-dimethyltryptamine, or DMT—is an amine found in chacruna leaves. Ingested on its own, it has no effect on humans, because it is rapidly degraded by an enzyme in the gut, monoamine oxidase. B. caapi vines, however, happen to contain potent monoamine-oxidase inhibitors (MAOI). Some ayahuasca enthusiasts maintain that the synergy was discovered thousands of years ago, when the spirit of the plants led indigenous people to brew the two together; others think that one day someone happened to drop a chacruna leaf into his B. caapi tea, a psychedelic version of “There’s chocolate in my peanut butter.” However the combination came about, it allows DMT access to the human brain: when a person drinks ayahuasca, a plant-messenger molecule targets the neurons that mediate consciousness, facilitating what devotees describe as a kind of interspecies communication. If the plant really is talking to the person, many people hear the same thing: we are all one. Some believe that the plants delivering this message are serving their own interests, because if humans think we are one with everything we might be less prone to trash the natural world. In this interpretation, B. caapi and chacruna are the spokesplants for the entire vegetable kingdom. But this sensation of harmony and interconnection with the universe—what Freud described as the “oceanic feeling”—is also a desirable high, as well as a goal of many spiritual practices. Since 2014, Draulio de Araujo, a researcher at the Brain Institute, in Natal, Brazil, has been investigating the effects of ayahuasca on a group of eighty people, half of whom suffer from severe depression. “If one word comes up, it is ‘tranquillity,’ ” he said. “A lot of our individuals, whether they are depressed or not, have a sense of peace after the experience.” Having studied fMRIs and EEGs of subjects on ayahuasca, Araujo thinks that the brain’s “default-mode network”—the system that burbles with thought, mulling the past and the future, while your mind isn’t focussed on a task—is temporarily relieved of its duties. Meanwhile, the thalamus, which is involved in awareness, is activated. The change in the brain, he notes, is similar to the one that results from years of meditation. Dennis McKenna told me, “In shamanism, the classic theme is death and rebirth—you are reborn in a new configuration. The neuroscientific interpretation is exactly the same: the default-mode network is disrupted, and maybe things that were mucking up the works are left behind when everything comes back together.” In the early nineties, McKenna, Charles Grob, a professor of psychiatry and pediatrics at Harbor-U.C.L.A. Medical Center, and James Callaway, a pharmaceutical chemist, conducted a study in Manaus, Brazil, that investigated the effects of ayahuasca on long-term users. Fifteen men who had taken part in bimonthly ceremonies for at least a decade were compared with a control group of people with similar backgrounds. The researchers drew blood from the subjects and assessed the white blood cells, which are powerful indicators of the condition of the central nervous system. (McKenna told me, “In psychopharmacology, we say, ‘If it’s going on in the platelets, it’s probably going on in the brain.’ ”) They found that the serotonin reuptake transporters—the targets that many contemporary antidepressants work on—were elevated among habitual ayahuasca drinkers. “We thought, What does this mean?” McKenna said. They couldn’t find any research on people with abnormally high levels of the transporters, but there was an extensive body of literature on low levels: the condition is common among those with intractable depression, and in people who suffer from Type 2 alcoholism, which is associated with bouts of violent behavior. “We thought, Holy shit! Is it possible that the ayahuasca actually reverses these deficits over the long term?” McKenna pointed out that no other known drug has this effect. “There’s only one other instance of a factor that affects this upregulation—and that’s aging.” He wondered if ayahuasca is imparting something to its drinkers that we associate with maturity: wisdom. Charles Grob told me, “Some of these guys were leading disreputable lives and they became radically transformed—responsible pillars of their community.” But, he noted, the men were taking ayahuasca as part of a religious ceremony: their church, União do Vegetal, is centered on integrating the ayahuasca experience into everyday life. Grob cautioned, “You have to take it with a facilitator who has some knowledge, experience, and ethics.” In unregulated ceremonies, several women have been molested, and at times people have turned violent. Last year, during a ceremony at an ayahuasca center in Iquitos, Peru, a young British man started brandishing a kitchen knife and yelling; a Canadian man who was also on ayahuasca wrestled it from him and stabbed him to death. Grob speculated that the shaman in that case had spiked the ayahuasca. Often, when things go wrong, it is after a plant called datura is added to the pharmacological mix. “Maybe facilitators think, Oh, Americans will get more bang for their buck,” Grob said. He also wondered if the knife-wielding British man had been suffering a psychotic break: like many hallucinogens, ayahuasca is thought to have the potential to trigger initial episodes in people who are predisposed to them. Problems can also arise if someone takes ayahuasca—with its potent MAOI—on top of selective serotonin reuptake inhibitors, a common class of antidepressants. The simultaneous blocking of serotonin uptake and serotonin degradation encourages enormous amounts of the neurotransmitter to flood the synapses. The outcome can be disastrous: a condition called serotonin syndrome, which starts with shivering, diarrhea, hyperthermia, and palpitations and can progress to muscular rigidity, convulsions, and even death. “I get calls from family members or friends of people who seem to be in a persistent state of confusion,” Grob said. He had just received a desperate e-mail from the mother of a young woman who had become disoriented in the midst of a ceremony. “She ran off from where she was, and when she was found she was having breathing difficulties and is now having what appears to be a P.T.S.D. reaction.” These cases are rare, but profoundly upsetting trips are common. People on ayahuasca regularly report experiencing their own death; one man told Araujo that he had a terrifying visualization of being trapped in a coffin. “There are some people who are getting damaged from it because they’re not using it the right way,” Dennis McKenna warned. “It’s a psychotherapeutic process: if they don’t integrate the stuff that comes up, it can be very traumatic. That’s the whole thing with ayahuasca—or any psychedelic, really. Set and setting is all-important: they’ve been telling us this since Leary! It’s not to be treated lightly.” “I’ll see your two and raise you three.”