“When I started it, they all just called it that crap. Like, ‘Oh, they’re over there doing that crap.’ ” This nurse, whom I’ll call Jamie, was on the line from a Veterans Affairs medical center in the Northeast. She’d been struggling for a few minutes between the impulse to tout the program she’d piloted, which offers Reiki to vets as part of their medical care, and the impulse to “tread lightly,” because some of the doctors, nurses, and administrators she works with still think that Reiki is quackery or—you know.

Reiki, a healing practice codified in the early 20th century in Japan, was until recently an unexpected offering for a VA medical center. In Japanese, rei roughly translates to “spiritual”; ki is commonly translated as “vital energy.” A session often looks more like mysticism than medicine: Healers silently place their hands on or over a person’s body to evoke a “universal life force.” A Reiki treatment can even, practitioners believe, be conducted from miles away.

Reiki’s growing popularity in the U.S.—and its acceptance at some of the most respected American hospitals—has placed it at the nexus of large, uneasy shifts in American attitudes toward our own health care. Various non-Western practices have become popular complements to conventional medicine in the past few decades, chief among them yoga, meditation, and acupuncture, all of which have been the subject of rigorous scientific studies that have established and explained their effectiveness. Reiki is the latest entrant into the suite of common additional treatments. Its presence is particularly vexing to naysayers because Reiki delivers demonstrable salutary effects without a proven cause.

Over the past two decades, a number of studies have shown that Reiki treatments help diminish the negative side effects of chemotherapy, improve surgical outcomes, regulate the autonomic nervous system, and dramatically alter people’s experience of physical and emotional pain associated with illness. But no conclusive, peer-reviewed study has explained its mechanisms, much less confirmed the existence of a healing energy that passes between bodies on command. Nevertheless, Reiki treatment, training, and education are now available at many esteemed hospitals in the United States, including Memorial Sloan Kettering, Cleveland Clinic, New York Presbyterian, the Yale Cancer Center, the Mayo Clinic, and Brigham and Women’s Hospital.

When Jamie introduced Reiki at the VA center 10 years ago, she overrode the objections of some colleagues who thought it was pseudoscience and out of step with the general culture of the VA, where people are inclined to be suspicious of anything that might be described as “woo woo.” But she insisted that the VA—which also offers yoga, acupuncture, massage, clinical hypnosis, and tai chi—should explore any supplementary treatment for chronic pain and PTSD that doesn’t involve pharmaceuticals, especially narcotics. The veterans started coming, slowly, and the ones who came started coming back. Jamie didn’t promise anything other than that it might help them feel calm or help them with pain. The Reiki practitioner she hired was a local woman, somewhat hard-nosed, not inclined to offer anyone crystals. Soon after the program began, Jamie was getting calls from doctors and nurses: “Hey, is the lady here? Someone wants that crap.”

The effects were startling, Jamie told me. Veterans who complained that their body had “forgotten how to sleep” came in for Reiki and were asleep on the table within minutes. Others reported that their pain declined from a 4 to a 2, or that they felt more peaceful. One patient, a man with a personality disorder who suffers from cancer and severe pain, tended to stop his normal routine of screaming and yelling at the staff when he came in for his Reiki sessions.

Popular though her program has become, Jamie still hears from colleagues who dismiss the results of Reiki as either incomprehensible or attributable to the placebo effect. As we talked, a little noise of frustration came through the phone line. We take people seriously when they say they’re in terrible pain, even though we can’t measure that, she said. “Why do we have a problem accepting when somebody says, ‘I feel better; that helped’?”

I first learned of Reiki six or seven years ago from a slim memoir by the writer Amy Fusselman. In 8: All True, Unbelievable, she describes receiving Reiki after years of psychotherapy and visits to doctors failed to ease what ailed her. “Doctors, in my experience, touch you with the desire to examine you, and then they use their brains to figure out what to do,” Fusselman writes.

This is fine, but right then it wasn’t what I wanted. What I wanted was to lie there and not use my brain, and believe someone was trying to help me, also not with his or her brain. I understand how this sounds. But you have to remember that I had been trying to use my brain on my problems for twenty years … I was over my brain. I was over everybody’s brain.

Reading this, I felt a prick of interest. I, too, was over my brain, which has always been as much the cause of my problems as the solution. What would it be like to admit the possibility of being made better by something that wasn’t pharmacological or physiotherapeutic or any of the many polysyllabic options readily available at my doctors’ offices? I believe, I suppose, in the spirit; and if I believe that people have a spirit as well as a body, then I might be willing to believe that feeling better or being well isn’t only a matter of adjusting the body.

This notion felt mildly outré in 2013, though the idea had long anchored Western medicine, until it parted ways in the 19th century with the holistic approach of Chinese medicine and the Hindu system of Ayurveda. Roberta Bivins points out in her history of alternative medicine that for most of Western history, medical wisdom held that physical health relied on the balance of the four humors (blood, black bile, yellow bile, and phlegm). Those in turn were affected by emotions, weather, the position of the stars, and faith just as much as by diet, age, activity, and environment. Reiki’s healing touch also has precedent. In the fourth or fifth century b.c., a Greek physician, possibly Hippocrates, included the following observation in some notes on his profession:

It is believed by experienced doctors that the heat which oozes out of the hand, on being applied to the sick, is highly salutary … It has often appeared, while I have been soothing my patients, as if there was a singular property in my hands to pull and draw away from the affected parts aches and diverse impurities … Thus it is known to some of the learned that health may be implanted in the sick by certain gestures, and by contact, as some diseases may be communicated from one to another.

This passage is now part of what’s called the Hippocratic Corpus, a series of texts written by or closely linked to Hippocrates, commonly known as the father of Western medicine. The precepts laid down there form the foundations of the medical philosophies that shape our health care today.

The Hippocratic Corpus also contains one of the earliest articulations of causal determinism, or the idea that all phenomena have a preexisting material cause. In the section titled “On the Sacred Disease,” the author insists that the illness we now recognize as epilepsy wasn’t a divine affliction at all, as it was believed to be at the time, but a physical ailment like any other, only with as-yet-mysterious causes. “Under a close examination spontaneity disappears,” the author writes, “for everything that occurs will be found to do so through something.”

The text doesn’t explicitly juxtapose these two notions—healing energy and causal determinism—or attempt to resolve any friction that may exist between them. Instead, it suggests that both are true at once: Everything that happens has a natural cause, and some people have a radiating heat in their hands that has curative power.

Even in the early and mid-19th century, physicians were still using humoral theory and competing with homeopaths and botanists for patients; surgeons were a crude last resort. This changed with the ascendancy of germ theory later in the century, when physicians—now focused on professionalizing their field—advanced a new, scientific medicine that they said was beyond dogma. It stood superior to its competitors because it was experimental and rational, requiring no faith—medicine as anti-mysticism.

Since then, the Yale historian of medicine Naomi Rogers told me, what is often called orthodox medicine has staked out “quackery” as its enemy. People continued to go to homeopaths and other extramedical practitioners with their health problems, of course. But after the 19th century, those who put stock in health care that wasn’t based in hard science were deemed ignorant. Physicians are still frustrated by such resistance today, Rogers said, but now when patients insist on a course of action other than what the doctor recommends, they’re called noncompliant.

The ranks of such patients have steadily grown, Bivins notes. Disillusionment with established medicine has been mounting for decades, fueled by the rising costs and more depersonalized care that have gone hand in hand with stunning technological advances and treatment breakthroughs. Eastern medicine and holistic healing models provided attractive alternatives to what critics in the late 1960s called the “medical industrial complex,” and by the new millennium extramedical “wellness” had become big business.

By the time I signed up last May to learn Reiki at a wellness center in Brooklyn, where I live, a $4.2 trillion global wellness industry had already harnessed the collective American obsession with optimizing the experience of having a body. We were putting adaptogens in our coffee, collagen in our smoothies, jade eggs in our vaginas. We were microdosing, supplementing, biohacking, juicing, cleansing, and generally trying to make ourselves immaculate from the inside out. I also noticed that the yoga studios and “healing spaces” in Brooklyn had begun to incorporate new kinds of offerings: breath work, energy healing, and especially Reiki.

The popularity of Reiki made sense as part of a backlash to the wellness explosion, which had lately come in for its share of debunking: It was a new form of consumption, critics argued, one that was more bound up with class, gender, anxiety, and late-stage capitalism than with actual health. Reiki takes only an hour or less; it entails no gear, no subscription, no purchases (other than the healer’s fee, which is often on a sliding scale according to income), no list of dietary strictures or dubious supplements. The practice could hardly be better pitched for the political and cultural mood: an anticonsumerist, egalitarian rite, available to everyone through mere breath and hands.

Reiki looked like the culmination of a broader trend that Rogers told me had been on the rise over the past 40 years, a development she calls a “black box” attitude toward healing. We submit to a treatment, it works on us mysteriously (as if in a black box), and we feel better. Rogers noted that we are most comfortable relinquishing ourselves to methods we don’t understand when the authority figure recommending them seems to care about us. What’s more, we have been acclimated to this form of trust by orthodox medicine.

Precision genetic medicine is inscrutable to laypeople, Rogers pointed out. Much of psychiatry resembles the black-box model too. So little is known, even by prescribing psychiatrists, about how and why psychotropic medications work in the brain. Yet the number of Americans who take SSRIs has been steadily rising over the past 30 years, despite a scientific consensus that the “serotonin imbalance” theory of depression is flawed—and despite a well-publicized controversy about whether the drugs are any more effective than placebos for most patients. Reiki is the perfect enactment of the black box, the healing gesture stripped to its essentials: a virtuous person sitting with you, intending your well-being in real time.

I signed up for instruction in two of Reiki’s three training levels. The first enables you to do hands-on practice on yourself as well as friends and family (and pets); the second introduces the mental technique for practicing at a distance. (Master training equips you to teach and “initiate” others.) The studio was a warehouse space, with whitewashed brick walls and plywood floors, exposed piping, and brightly colored garlands hanging along the windows. The windowsills were strewn with crystals, shells, and small bottles of oil diffusing into the air.

Once everyone had settled on seat cushions arranged in a large circle on the floor, the two women leading the training introduced the core belief: Reiki energy exists throughout the universe, and when the body is attuned to Reiki, it can act as a sort of lightning rod through which others can receive that energy. They told us to picture Reiki energy entering through the top of our head and exiting through our hands, suffusing us and whomever we touch with the intention to heal. The healer’s job is not to control the Reiki or to make decisions about healing. “We’re just the channel,” one of the masters said. “The healing is a contract between the person who needs to be healed and the higher power.” Reiki, they stressed, can never harm anyone. It should also be used only as a complement to conventional medicine, never as a replacement. “We are not doctors,” they said several times. “We cannot diagnose anyone with anything.”

You can do Reiki on animals, they told us. “Cats are extra attuned to Reiki—cats almost do Reiki on their own. They can heal you.” No one questioned this. The same goes for plants, the masters suggested. Get two roses and give Reiki to one; that rose will live longer. A student raised her hand. “But you told us never to give Reiki without consent. How can you get consent from a flower or a tree?”

“You can talk to a tree!” one of the masters said. “You should always ask the tree’s permission. Maybe it will tell you to Reiki the next tree.” I glanced around the room for raised eyebrows, but there were only more eager questions: Can you Reiki someone who has transitioned to the afterlife? Yes. Can you Reiki your food to make it healing? Yes, and you should.

We were told that once the masters attuned us, our bodies and spirits would vibrate at a higher frequency than before, and we would stay on that higher frequency for the rest of our life. This would constitute a permanent transition in our physical and spiritual states. I was silently indignant: I do not believe in permanently alterable personal vibrations, whatever that means, and anyway I wanted mine left alone.

The masters warned us that once they had opened us to Reiki energy, we should expect to feel a little emotionally drained and perhaps light-headed. They also suggested that many people experience drastic life changes after their first attunement. Major emotional issues come to the surface and require resolution; people suddenly lose their tolerance for alcohol or other drugs; friends, able to sense vibrations “on a different frequency,” distance themselves.

And then, the moment for attunement having arrived, we were led in small groups to a narrow, darkened room. Before we passed through the doorway, one of the masters traced Reiki symbols in the air over each of us. “You guys,” said the other, making what I hoped was a joke, “we’re going to visit some other planets.” I can’t describe what happened next, because our eyes were closed while the masters performed silent rituals that aren’t explained to nonmasters.

A few weeks later, I met with Pamela Miles, an international Reiki master and the leading expert on incorporating Reiki into medical care. Miles has been practicing Reiki since 1986. She has introduced programs into prestigious hospitals and taught Reiki at academic medical centers such as Harvard, Yale, and the National Institutes of Health. Miles has the soft voice, long hair, loose clothing, slow gestures, and easy smile characteristic of someone involved in healing arts. She also has the sharpness one sometimes observes in people who have devoted their life to a discipline—an exactitude and authority. When I told Miles about my training, she looked incredulous. “When they said you were going to have energy shooting through your head from the universe, were you scared?” This afternoon, she was patiently attempting to reeducate me.

Miles falls on the conservative end of Reiki evangelists in that she’s careful not to make claims about its mechanisms or efficacy that can’t be supported in a scientific context. She does not, for example, subscribe to the belief that Reiki energy is a substance that can be given, received, or measured. No evidence of this has been confirmed, she pointed out. “Reiki is a spiritual practice,” she said. “That’s what it was to the founder, Mikao Usui. And all spiritual practices have healing by-products because spiritual practice restores balance, bringing us back to our center, and enhancing our awareness of our core selves.” When I asked her to explain what that meant practically, she chose her words carefully. “Through an unknown mechanism, when a Reiki practitioner places their hands—mindfully and with detachment—it evokes the healing response from deep within the system,” she said. “We really don’t know why this happens.”

This agnosticism is not shared by all of Reiki’s powerful advocates in the United States. The array of psychologists, physicists, and physiologists on the boards of various national Reiki organizations I spoke with—many of whom are eager to develop a standardized method of training and accreditation—champion different forms of energy measurement. In conversations, I heard quantum physics invoked, as well as biophotons, sodium channels, and “magnetic stuckness,” and tools like EEGs and gamma-ray detectors. Ann Baldwin, a physiology professor at the University of Arizona and the editor in chief at the Center for Reiki Research, suggested that people who claim to have measured Reiki using energy-sensing machinery are instead measuring something else, such as heat—but she holds out hope that someday we may be able to measure Reiki.

Research this for too long, and you start to sound vaguely stoned. Is Reiki real? Does it matter whether Reiki is real? And whose definition of real are we working with: Is it real according to the presiding scientific and medical framework, which tells us that phenomena need to be measurable to be taken seriously, or is it real in the looser, unquantifiable way of spiritual practice?

There are those who will tell you that Reiki is absolutely real because people experience it to be real. It is real because we feel it, and feelings are produced in the body. Skeptics are quick to point to the placebo effect: The body’s capacity to heal itself after receiving only the simulated experience of medication or therapy is well documented. But precisely because that capacity is so well documented, reflexive dismissal of the placebo effect as “fake medicine” demands scrutiny—and is now receiving it. In late 2018, The New York Times Magazine reported on a group of scientists whose research suggests that responsiveness to placebos, rather than a mere trick of the mind, can be traced to a complex series of measurable physiological reactions in the body; certain genetic makeups in patients even correlate with greater placebo response. Ted Kaptchuk, a Harvard Medical School professor and one of the lead researchers, theorizes that the placebo effect is, in the words of the Times article, “a biological response to an act of caring; that somehow the encounter itself calls forth healing and that the more intense and focused it is, the more healing it evokes.”

To note that touch-based healing therapies, including Reiki, simulate the most archetypal care gestures is hardly a revelation. Several scientists I interviewed about their work on Reiki mentioned the way their mother would lay a hand on their head when they had a fever or kiss a scraped knee and make the pain go away. It is not hard to imagine that a hospital patient awaiting surgery or chemotherapy might feel relieved, in that hectic and stressful setting, to have someone place a hand gently and unhurriedly where the hurt or fear is with the intention of alleviating any suffering. That this increased calm might translate into lowered blood pressure or abated pain, anxiety, or bleeding—as has been observed in hospital patients who undergo Reiki—seems logical, too.

The ailments that Reiki seems to treat most effectively are those that orthodox medicine struggles to manage: pain, anxiety, chronic disease, and the fear or discomfort of facing not only the suffering of illness but also the suffering of treatment. “What conventional medicine is excellent at is acute care. We can fix broken bones, we can unclog arteries, we can help somebody survive a significant trauma, and there are medicines for all sorts of symptoms,” Yufang Lin, an integrative-medicine specialist at Cleveland Clinic, told me. But medicine, she said, is less successful at recognizing the way that emotion, trauma, and subjective experience can drive physical health—and the way that they can affect recovery from acute medical care.

Lifesaving surgery is miraculous but requires drugging the body, cutting it open, altering it, stitching it back together, and then asking it to heal. Chemotherapy causes the body to fall to pieces; it can damage the brain, wreck internal organs, and destroy nerve endings, sometimes permanently. Medicine is necessary, but it can also be brutal. Lin, like several of the physicians I spoke with, emphasized that healing is something that happens within the body, enabled rather than imposed by medicine. When we are traumatized, survival is the priority and our healing mechanisms are on lockdown, Miles observed. “We have to pull out of that stress state and get into a parasympathetic-dominant state before the body is able to self-heal and actively partner with conventional medicine.”

Many physicians and scientists still believe that allowing Reiki to share space with medicine is at best silly and at worst dangerous. In 2014, David Gorski, a surgical oncologist, and Steven Novella, a neurologist, co-wrote an article calling for an end to clinical trials of Reiki and other forms of energy medicine. To assess approaches rooted in “prescientific thinking” with tools designed to evaluate “well-supported science- and evidence-based” treatments, they argued, degrades “the scientific basis of medicine.” It saps resources from research into valid therapies, and misleads patients.

Other doctors and researchers have accepted the line of argument that Miles and many other Reiki advocates have put forward: The practice has no known negative side effects, and has been shown by various studies that pass evidentiary muster to help patients in a variety of ways when used as a complementary practice. Unlike the many FDA-approved medications that barely beat a placebo in studies and carry negative side effects, Reiki is cheap and safe to implement. Does its exact mechanism need to be understood for it to be accepted as a useful therapeutic option? For decades, experts weren’t precisely sure how acetaminophen (Tylenol) eases pain, but Americans still took billions of doses every year. Many medical treatments are adopted for their efficacy long before their mechanisms are known or understood. Why should this be different?

In the Reiki training I attended, the moment came when we began to practice on one another for the first time. Taking turns, students would hop up on the table, and four or five others would cluster around. The masters told us to breathe deeply, gather our intention, and begin. After one or two minutes of uncertain silence, a woman a few tables away from me spoke up. “What are we supposed to be thinking?”

I was relieved someone had asked. My entire reason for being in the class was to learn what a person is doing when practicing Reiki. But our teachers hadn’t said what, precisely, was supposed to transform the act of hovering our hands over one another into Reiki.

“You don’t have to be thinking anything,” one master said. “You are just there to love them.”

I thought to myself, more or less simultaneously, Oh brother and Of course. That we were simply there to be loving one another sounded like the worst stereotype of pseudo-spiritual babble. At the same time, this recalled the most cutting-edge, Harvard-stamped science I’d read in my research: Ted Kaptchuk’s finding that the placebo effect is a real, measurable, biological healing response to “an act of caring.” The question of what Reiki is introduces—or highlights—an elision between the spiritual and the scientific that has, as yet, no resolution.

In 2002, two professors at the University of Texas Health Science Center, in Houston, gathered a group of people in order to document and study the qualitative experience of receiving a Reiki treatment. The study participants didn’t have any shared belief in Reiki or its possible results, or any particular need for healing; they simply received a session and then described what they felt.

After treatment, the subjects spoke more slowly. They described their experience in the language of paradoxes. “In the normal state of awareness, especially in Western traditions, people tend to see disparate phenomena as distinct, discrete, and contradictory,” the authors of the study later wrote. “Most people resolve that disparity by denying or suppressing the existence of one of the poles.” But through Reiki, the subjects entered a liminal state, in which their thoughts seemed both like their own and not; time moved both very fast and very slowly; their bodies seemed no longer separate from the practitioner’s body, though they also remembered that their bodies were their own.

At the end of my training, I did not feel invested with any new power, but I did feel raw and buzzy. Though plenty of things in my training had seemed flatly impossible to believe, I had spent lots of time on a table as a practice body for my classmates. I’d felt more relaxed and calm afterward, but did I feel healed? Healed of what? Healed by what? I’d spent even more time breathing deeply and placing hands on a stranger’s solar plexus, or the crown of her head, or the arch of her foot. In that time, I had sometimes felt nothing other than the comfort of human touch. Other times I had felt odd things: the sensation of magnetic attraction or repulsion between my hand and a rib cage, a burning heat that came and went suddenly. When I gently cupped my hands around a woman’s jaw, the tips of my right fingers buzzed as if from an electrical current, tickling me.

I had spent two days in and out of the liminal state the UT study described, and I felt more sensitive to the world. I had also spent some meaningful time being touched kindly by strangers and touching them kindly, and thinking about what it might be like to feel well, to stop reporting to the doctor every year the same minor ailments: a tweaked shoulder, a tight jaw, general nervousness, scattered attention, my idiosyncratic imbalances and deficiencies. I didn’t personally “believe” in Reiki as a universal energy channeled through the hands, available to cats and plants and the dead. But I believed Yufang Lin and other physicians who attest that the body—helped by medicine and nutrition and all sorts of things—does the work of healing, and I believed Miles when she said that Reiki practice, through some unknown mechanism, may help the body to do it.

Every once in a while, friends will hear that I’m Reiki-trained and ask whether I’ll “do it” on them. They usually ask whether it’s real, and I say I don’t know, but that at a minimum, I’ll have spent some time quietly and gently focusing on the idea of them being well. They usually answer that this sounds good.

Jordan Kisner is a writer in New York City.