Psilocybin may be useful in treating anxiety, addiction, and depression, and in studying the neurobiology of mystical experience. Illustration by Stephen Doyle

On an April Monday in 2010, Patrick Mettes, a fifty-four-year-old television news director being treated for a cancer of the bile ducts, read an article on the front page of the Times that would change his death. His diagnosis had come three years earlier, shortly after his wife, Lisa, noticed that the whites of his eyes had turned yellow. By 2010, the cancer had spread to Patrick’s lungs and he was buckling under the weight of a debilitating chemotherapy regimen and the growing fear that he might not survive. The article, headlined “Hallucinogens Have Doctors Tuning in Again,” mentioned clinical trials at several universities, including N.Y.U., in which psilocybin—the active ingredient in so-called magic mushrooms—was being administered to cancer patients in an effort to relieve their anxiety and “existential distress.” One of the researchers was quoted as saying that, under the influence of the hallucinogen, “individuals transcend their primary identification with their bodies and experience ego-free states . . . and return with a new perspective and profound acceptance.” Patrick had never taken a psychedelic drug, but he immediately wanted to volunteer. Lisa was against the idea. “I didn’t want there to be an easy way out,” she recently told me. “I wanted him to fight.”

Patrick made the call anyway and, after filling out some forms and answering a long list of questions, was accepted into the trial. Since hallucinogens can sometimes bring to the surface latent psychological problems, researchers try to weed out volunteers at high risk by asking questions about drug use and whether there is a family history of schizophrenia or bipolar disorder. After the screening, Mettes was assigned to a therapist named Anthony Bossis, a bearded, bearish psychologist in his mid-fifties, with a specialty in palliative care. Bossis is a co-principal investigator for the N.Y.U. trial.

After four meetings with Bossis, Mettes was scheduled for two dosings—one of them an “active” placebo (in this case, a high dose of niacin, which can produce a tingling sensation), and the other a pill containing the psilocybin. Both sessions, Mettes was told, would take place in a room decorated to look more like a living room than like a medical office, with a comfortable couch, landscape paintings on the wall, and, on the shelves, books of art and mythology, along with various aboriginal and spiritual tchotchkes, including a Buddha and a glazed ceramic mushroom. During each session, which would last the better part of a day, Mettes would lie on the couch wearing an eye mask and listening through headphones to a carefully curated playlist—Brian Eno, Philip Glass, Pat Metheny, Ravi Shankar. Bossis and a second therapist would be there throughout, saying little but being available to help should he run into any trouble.

I met Bossis last year in the N.Y.U. treatment room, along with his colleague Stephen Ross, an associate professor of psychiatry at N.Y.U.’s medical school, who directs the ongoing psilocybin trials. Ross, who is in his forties, was dressed in a suit and could pass for a banker. He is also the director of the substance-abuse division at Bellevue, and he told me that he had known little about psychedelics—drugs that produce radical changes in consciousness, including hallucinations—until a colleague happened to mention that, in the nineteen-sixties, LSD had been used successfully to treat alcoholics. Ross did some research and was astounded at what he found.

“I felt a little like an archeologist unearthing a completely buried body of knowledge,” he said. Beginning in the nineteen-fifties, psychedelics had been used to treat a wide variety of conditions, including alcoholism and end-of-life anxiety. The American Psychiatric Association held meetings centered on LSD. “Some of the best minds in psychiatry had seriously studied these compounds in therapeutic models, with government funding,” Ross said.

Between 1953 and 1973, the federal government spent four million dollars to fund a hundred and sixteen studies of LSD, involving more than seventeen hundred subjects. (These figures don’t include classified research.) Through the mid-nineteen-sixties, psilocybin and LSD were legal and remarkably easy to obtain. Sandoz, the Swiss chemical company where, in 1938, Albert Hofmann first synthesized LSD, gave away large quantities of Delysid—LSD—to any researcher who requested it, in the hope that someone would discover a marketable application. Psychedelics were tested on alcoholics, people struggling with obsessive-compulsive disorder, depressives, autistic children, schizophrenics, terminal cancer patients, and convicts, as well as on perfectly healthy artists and scientists (to study creativity) and divinity students (to study spirituality). The results reported were frequently positive. But many of the studies were, by modern standards, poorly designed and seldom well controlled, if at all. When there were controls, it was difficult to blind the researchers—that is, hide from them which volunteers had taken the actual drug. (This remains a problem.)

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By the mid-nineteen-sixties, LSD had escaped from the laboratory and swept through the counterculture. In 1970, Richard Nixon signed the Controlled Substances Act and put most psychedelics on Schedule 1, prohibiting their use for any purpose. Research soon came to a halt, and what had been learned was all but erased from the field of psychiatry. “By the time I got to medical school, no one even talked about it,” Ross said.

The clinical trials at N.Y.U.—a second one, using psilocybin to treat alcohol addiction, is now getting under way—are part of a renaissance of psychedelic research taking place at several universities in the United States, including Johns Hopkins, the Harbor-U.C.L.A. Medical Center, and the University of New Mexico, as well as at Imperial College, in London, and the University of Zurich. As the drug war subsides, scientists are eager to reconsider the therapeutic potential of these drugs, beginning with psilocybin. (Last month The Lancet, the United Kingdom’s most prominent medical journal, published a guest editorial in support of such research.) The effects of psilocybin resemble those of LSD, but, as one researcher explained, “it carries none of the political and cultural baggage of those three letters.” LSD is also stronger and longer-lasting in its effects, and is considered more likely to produce adverse reactions. Researchers are using or planning to use psilocybin not only to treat anxiety, addiction (to smoking and alcohol), and depression but also to study the neurobiology of mystical experience, which the drug, at high doses, can reliably occasion. Forty years after the Nixon Administration effectively shut down most psychedelic research, the government is gingerly allowing a small number of scientists to resume working with these powerful and still somewhat mysterious molecules.

As I chatted with Tony Bossis and Stephen Ross in the treatment room at N.Y.U., their excitement about the results was evident. According to Ross, cancer patients receiving just a single dose of psilocybin experienced immediate and dramatic reductions in anxiety and depression, improvements that were sustained for at least six months. The data are still being analyzed and have not yet been submitted to a journal for peer review, but the researchers expect to publish later this year.

“I thought the first ten or twenty people were plants—that they must be faking it,” Ross told me. “They were saying things like ‘I understand love is the most powerful force on the planet,’ or ‘I had an encounter with my cancer, this black cloud of smoke.’ People who had been palpably scared of death—they lost their fear. The fact that a drug given once can have such an effect for so long is an unprecedented finding. We have never had anything like it in the psychiatric field.”

I was surprised to hear such unguarded enthusiasm from a scientist, and a substance-abuse specialist, about a street drug that, since 1970, has been classified by the government as having no accepted medical use and a high potential for abuse. But the support for renewed research on psychedelics is widespread among medical experts. “I’m personally biased in favor of these type of studies,” Thomas R. Insel, the director of the National Institute of Mental Health (N.I.M.H.) and a neuroscientist, told me. “If it proves useful to people who are really suffering, we should look at it. Just because it is a psychedelic doesn’t disqualify it in our eyes.” Nora Volkow, the director of the National Institute on Drug Abuse (nida), emphasized that “it is important to remind people that experimenting with drugs of abuse outside a research setting can produce serious harms.”