In the fall of 1972, a psychiatrist named Salvador Roquet travelled from his home in Mexico City to the Maryland Psychiatric Research Center, an institution largely funded by the United States government, to give a presentation on an ongoing experiment. For several years, Roquet had been running a series of group-therapy sessions: over the course of eight or nine hours, his staff would administer psilocybin mushrooms, morning-glory seeds, peyote cacti, and the herb datura to small groups of patients. He would then orchestrate what he called a “sensory overload show,” with lights, sounds, and images from violent or erotic movies. The idea was to push the patients through an extreme experience to a psycho-spiritual rebirth. One of the participants, an American psychology professor, described the session as a “descent into hell.” But Roquet wanted to give his patients smooth landings, and so, eventually, he added a common hospital anesthetic called ketamine hydrochloride. He found that, given as the other drugs were wearing off, it alleviated the anxiety brought on by these punishing ordeals.

Clinicians at the Maryland Psychiatric Research Center had been studying LSD and other psychedelics since the early nineteen-fifties, beginning at a related institution, the Spring Grove Hospital Center. But ketamine was new: it was first synthesized in 1962, by a researcher named Calvin Stevens, who did consulting work for the pharmaceutical company Parke-Davis. (Stevens had been looking for a less volatile alternative to phencyclidine, better known as PCP.) Two years later, a doctor named Edward Domino conducted the first human trials of ketamine, with men incarcerated at Jackson State Prison, in Michigan, serving as his subjects. At higher doses, Domino noticed, ketamine knocked people out, but at lower ones it produced odd psychoactive effects on otherwise lucid patients. Parke-Davis wanted to avoid characterizing the drug as psychedelic, and Domino’s wife suggested the term “dissociative anesthetic” to describe the way it seemed to separate the mind from the body even as the mind retained consciousness. The F.D.A. approved ketamine as an anesthetic in 1970, and Parke-Davis began marketing it under the brand name Ketalar. It was widely used by the U.S. military during the Vietnam War, and remains a standard anesthetic in emergency rooms around the world.

Roquet found other uses for it. After his lecture in Maryland, he offered experiential training to the clinicians there. “I was introduced to the strangest psychoactive substance I have ever experienced in the 50 years of my consciousness research,” the psychiatrist Stanislav Grof recalls in “The Ketamine Papers,” a book edited by the psychiatrist Phil Wolfson and the researcher Glenn Hartelius. Grof subsequently experimented with ketamine personally, and found himself inhabiting the perspectives of a wet towel hanging on a railing overlooking the ocean, petroleum filling the cavities of the earth, and the prisms of a diamond. “In one of my ketamine sessions, I became a tadpole undergoing a metamorphosis into a frog, and in another one, a giant silverback gorilla claiming his territory,” Grof writes.

When the training took place, psychedelic research was already coming under legal threat. In 1968, the U.S. government outlawed possession of LSD; Richard Nixon announced a war on drugs three years later. In 1974, Roquet was jailed for several months in Mexico, and subsequently cut back on his group sessions. (He died in 1995.) The Maryland Psychiatric Research Center ended its psychedelic research in the mid-seventies, amid broader upheaval at the center.

But ketamine remained medically legal, and countercultural psychiatrists continued to experiment with it. In the eighties, the drug’s best-known enthusiast was John C. Lilly, a doctor and psychoanalyst perhaps most famous for using sensory-deprivation tanks and dabbling in human-dolphin communication. Lilly became addicted to ketamine: a researcher who crossed paths with him at the Esalen Institute, a retreat in Northern California, recalled Lilly spending most of his time in his Volkswagen minibus, where he was evidently injecting himself multiple times a day. (Lilly said that he stopped using the drug in his early sixties, on the orders of extraterrestrials, but he resumed taking it later in life. He died in 2001, at eighty-six.) During these years, ketamine also became a popular dance-floor drug. Partyers generally snorted it, at lower doses, for a less drastic and more interactive high, experiencing distortions of perception that have been described as “scenery slicing” and “environmental cubism.” Among clubgoers, taking so much that you became unaware of your surroundings—experiencing a “K-hole”—was typically considered a scary mistake. The drug became especially fashionable among ravers in the nineties, and, at the end of that decade, the U.S. government made ketamine a Schedule III substance, putting it on the same regulatory footing as steroids and Tylenol with codeine.

Meanwhile, clinicians at Yale, who were using the drug to mimic the symptoms of schizophrenia, noticed that ketamine improved people’s moods. Researchers began studying it as a treatment for depression, and, in 2006, the National Institute of Mental Health concluded that a single intravenous dose of ketamine had rapid antidepressant effects. Around three hundred clinical trials have since been held; the broad consensus is that ketamine relieves symptoms of depression for a period that can last days or weeks, during which time talk therapy often proves more effective than normal. Ketamine is what’s called a “dirty drug,” meaning that it acts on different parts of the brain at once, and there are several theories about how it works against depression, but most focus on its effects on certain receptors in the brain, and on the neurotransmitter glutamate. (One theory holds that ketamine modulates levels of a protein that can generate new neurons.) By 2010, doctors were recommending its off-label use to acutely suicidal patients, and ketamine clinics began opening around the country. These days, the research and debate surrounding ketamine are less concerned with whether it can treat depression than with how it works, which delivery method makes it most effective, and how drug companies and health-care providers might best profit off a substance whose patent expired in the nineteen-eighties.

One of the first clinics, New York Ketamine Infusions, was opened by Glen Brooks, a Harvard-trained anesthesiologist, in 2012. Brooks sometimes wears a white lab coat, and practices in an ordinary-looking doctor’s office, where he keeps jars of FireBall candies on his desk. (He used to sublet space from a podiatrist.) He’d been a physician for more than thirty years when a relative’s drug problems prompted him to pursue addiction medicine. After just a few months, he concluded that the field was hopeless when it came to addressing the childhood traumas that lead people to self-medicate. He read the early research on ketamine as a treatment for mood disorders and saw not only reason for optimism but a business opportunity.

Brooks administers ketamine by I.V., at subanesthetic doses, and only some of his patients have dissociative experiences. “There’s nothing therapeutic going on when they’re here,” he told me, when I visited him at his clinic on a rainy Sunday this past spring. Patients hooked up to I.V. drips were undergoing treatment in dimly lit rooms. “We’re growing dendrites and synapses,” he said. Brooks encourages his patients to bring a friend or listen to a podcast to distract themselves from ketamine’s psychoactive effects. He said that what patients happen to think about during their sessions doesn’t really matter.

This approach, which is typical of the early ketamine clinics, contrasts with the countercultural attitude that prevailed among the drug’s advocates in the seventies and in a new tide of startups. Beginning roughly with the publication of “How to Change Your Mind,” a best-selling book by Michael Pollan, in 2018, psychedelic treatments for mental health have gone mainstream. Publicly traded companies, such as Compass Pathways and MindMed, have begun patenting variations on psychedelic treatments. Last fall, Peter Thiel was among the investors in a hundred-and-twenty-five-million-dollar round of funding for the biotech company atai Life Sciences, which principally focusses on the use of psychedelics in the treatment of mental illness; in June, the company went public, and was valued at more than three billion dollars.

In recent years, I have watched many people in my life quit antidepressants and start microdosing LSD and mushrooms, informed by exuberant news reports and the encouraging but not yet conclusive data documented in Pollan’s book and elsewhere. Most of these people are skeptical of the pharmaceutical industry and desperate to find more pleasure in life; for some, coding substance use as an antidepressant routine, and ingesting very tiny doses, seems to suit a sense of middle-class propriety and upwardly mobile productivity. (The doctors I spoke with by and large agreed that ketamine—which a number of outlets have proclaimed the “It Drug” of personal use during the pandemic—does not have the same clinically proven antidepressant effects when snorted.)

To view this video please enable JavaScript, and consider upgrading to a web browser that supports HTML5 video

It is also, unlike LSD and mushrooms, legal for medical use throughout the U.S., and so provides the only avenue for American medical providers to generate revenue with psychedelic substances. (In 2019, the F.D.A. approved Spravato, from Johnson & Johnson, which contains one of the two molecules in the original ketamine formulation, and which will allow the company to sell a more profitable, if not necessarily more effective, version of the drug.) Today, a self-referring depressive with several hundred dollars on hand who is not in the throes of active mania or psychosis can seek out a wide array of clinical treatments with the drug: a titrated dose given intravenously by an anesthesiologist at a retail clinic, a shot in the arm from a psychiatrist in private practice, an oral lozenge sent in the mail by a startup taking advantage of pandemic-era changes to the regulation of remote prescriptions. If you can get to the right city, and have sufficient funds, you can easily secure a legal, therapist-guided, mind-expanding trip at a clinic that advertises on Facebook and is funded by venture capital.

The New York office of Field Trip Health, which opened in August, 2020, is situated in the Kips Bay neighborhood of Manhattan. It occupies the entire eleventh floor of a building next to Baruch College, and has big windows and a wraparound terrace. The decorative touches are spa-like: white rugs, fiddle-leaf figs, electric candles inside glass-paned lanterns. The aesthetic seems based on the assumption that, when a company hopes to take a formerly taboo practice mainstream, a West Elm interior can go a long way.

When I visited, this past spring, Matt Emmer, Field Trip’s vice president of health-care practice, showed me around—he was wearing a floral button-down of the sort that I associate with tech-company business casual. Field Trip was founded, in April, 2019, by five Canadian entrepreneurs, four of whom previously founded a chain of cannabis-dispensing medical clinics. The company now operates ten ketamine clinics in Canada and the U.S., with plans to open several more in the near future. (Field Trip recently opened a clinic in Amsterdam that offers patients guided-therapy sessions with magic mushrooms.) The company has a research and development wing, Field Trip Discovery, which is devoted to the cultivation of psilocybin mushrooms and the development of psychedelic-inspired medicines; this work is being done at a laboratory at the University of the West Indies, in Mona, Jamaica, where the drug laws are relatively forgiving. Field Trip recently filed a patent for a molecule called FT-104, which, according to preclinical experiments, targets the same serotonin receptor as psilocybin, but has much briefer effects. A drug trip that lasts two hours offers a far more viable business model than one that lasts five or six.

Emmer walked me down a hallway where the sound of water burbled from a white-noise machine, and he told me that he took interior-design cues from nature (“something that’s universal”). In the reception area, I saw copies of “How to Change Your Mind” for sale alongside “Be Here Now,” by the psychedelic guru Ram Dass. But, for the most part, signs of the counterculture were muted. Emmer led me into a windowless room. On one wall was a mural of spider monkeys peeking through palm fronds. In a corner, there was a large, white leather, zero-gravity chair. I sat down, and, at Emmer’s invitation, pressed a button on a remote. The chair made a soothing hum and slowly tipped backward, ready to carry me across the threshold of consciousness in its arms. “It makes you feel as weightless as possible without going into space,” Emmer said. This was one of the treatment rooms.

Sitting where the therapist normally would, Emmer explained the process. A patient arrives and selects from a menu of guided meditations and light therapy as a way of easing in before her trip. Ketamine is then administered with one or two intramuscular shots—the mind-altering equivalent of a rocket launch. The patient puts on noise-cancelling headphones, a weighted blanket, and an eye mask, and turns inward, listening to a soundtrack of nonverbal music. (One playlist is mostly classical and another is electronic; the music is intentionally obscure, to avoid provoking personal associations.)

I pressed another button on the remote, and Emmer waited as my chair slowly returned to its upright position. After the ketamine subsides, he explained, the patient sits for a session of talk therapy. The entire round of treatment lasts between two and three hours. A lounge stocked with mandala coloring books and watercolors offers a restful place to come back to earth before going home. Like most ketamine clinics, Field Trip encourages an initial set of four to six infusions spaced out across two to four weeks, with boosters available on an as-needed basis thereafter. The first session costs seven hundred and fifty dollars and subsequent treatments cost a thousand. The patient is paying for the therapy more than the drug, which costs as little as seven dollars a dose.

Earlier this year, a thirty-five-year-old filmmaker I know signed up for ketamine-assisted therapy at Field Trip. She had been reading about psychedelics during the pandemic. She read the Pollan book and a memoir called “The Wild Kindness: A Psilocybin Odyssey.” She listened to a lot of podcasts. She had tried LSD and mushrooms before. On those trips, she felt expansive and connected to the cosmos; she looked at the clouds, which seemed to be moving backward, and at the moon, which appeared more three-dimensional than usual. She wanted to undergo other shifts in her perspective. She was experiencing a degree of anxiety and obsessive thinking—she takes antidepressants and has more than a decade of therapy in her past—but she did not believe that she had any urgent mental-health issues. “I’m actually in a good place in my life right now,” she told me, “and it’s more about wanting to take it to the next level.” She contacted an underground therapist about a supervised mushroom trip, but the waitlist was two years long. “This was the path of least resistance,” she explained to me, of Field Trip. “I literally typed something into Google.” She underwent two screenings with the clinic, the first of which focussed on what ketamine is and what it can offer, and the second of which, she told me, was “about making sure you’re not crazy or you’re not going to kill yourself afterward.”

Her first session was scheduled for June. I spoke to her later that week. The experience had been more intense than what she was expecting. Her intake sessions were conducted virtually, so the day of her trip was her first visit to the office. An employee showed her a chair with a kind of helmet that descends upon the sitter’s head and provides a choice of colored lights to set the mood for meditation. She saw a glass table with a tray underneath it, in which a self-propelled metal ball traced patterns in sand. “I felt like I was already tripping when I went in there,” she told me. She found the burbling water sounds from the white-noise machine unnerving.