Despite the fact that psychedelic drugs have been used for millennia as medicine in ritualistic ceremonies, there remain many questions in the scientific community about the relationship between their spiritual qualities and healing potential. Researchers at Johns Hopkins and New York Universities are giving psilocybin, the active ingredient in magic mushrooms, to ordained ministers in the hopes that they can help provide some answers.

So far, they have enrolled thirteen religious leaders including an Orthodox Jewish rabbi, a Zen Buddhist roshi, an Episcopalian, a Greek Orthodox priest, and a Reform Christian for their FDA-approved clinical trial. (They’re also seeking Catholic priests, Imams, and Hindu priests to join the study.)

The researchers, who are dividing the psilocybin sessions between their two universities, plan to see if these ministers can use their spiritual practice and the vocabulary of religious study to provide insight into those sacred psychedelic moments that so often seem to transcend words. They’re also hoping to gain insight into the broader benefits of mystical experiences—and it turns out, there may not be much of a difference between ones that are drug-induced and those that arise organically.

Using a survey widely administered by religious scholars, the researchers have found consistent overlap between mystical experiences that occur naturally and those that are caused by psilocybin. “All we’re doing is finding conditions that increase the likelihood of these mystical experiences, and we still don’t know their ultimate cause,” says Roland Griffiths, a principal investigator across multiple Johns Hopkins psilocybin trials.

Researchers have found consistent overlap between mystical experiences that occur naturally and those that are caused by psilocybin.

Scientists are no closer today to agreeing on the purpose of profound religious experiences than they were when William James, often called the father of American psychology, published the first systematic investigation of them in 1902. In his seminal text The Varieties of Religious Experience, James called on his colleagues to abandon their over-reliance on “medical materialism”—the reduction of psychology to processes in the body—and acknowledge the therapeutic value of spiritual encounters, even if their origins remained elusive. James’s descriptions of the ways in which people find long-lasting happiness and increased selflessness following mystical experiences share remarkable similarities with the reported effects of psilocybin sessions.

But since modern psychology was founded in the late 1800s, there have been limitations to studying spiritual encounters. Namely: They’re rare. And while stories across generations provide evidence that practices such as meditation, fasting, and prayer can help induce spiritual reveries, they’re also largely unpredictable. But a growing body of evidence is finding that psychedelic drugs might play a key role in understanding these moments which have eluded scientists for so long.

In a widely reported trial published in December 2016, the degree to which cancer patients saw a decrease in anxiety, depression, and a fear of death directly correlated with the intensity of their mystical experience on psilocybin. Similarly, in a six-month follow-up with cigarette smokers who underwent psilocybin sessions, the greater their mystical experience, the less they reported cravings to smoke afterward.

Johns Hopkins has also studied the effects of psilocybin in healthy volunteers. In these three trials—as in the research with the cancer patients and cigarette smokers—the data shows that mystical experiences give rise to positive changes in mood, altruism, forgiveness, and interpersonal closeness, among other qualities. Two-thirds or more of the participants rate one of their sessions among the top five most meaningful experiences of their life alongside events such as the birth of a first child. As the researchers point out, psilocybin only lasts about eight hours, but the effects of it persist for years. This means it’s likely not the drug itself, but the memory of the experience on the drug that is increasing people’s well-being.

Mystical experiences give rise to positive changes in mood, altruism, forgiveness, and interpersonal closeness.

According to cognitive scientist and religion scholar Justin Lane, the relationship between religiosity and well-being has been “well-established.” A 2016 study from the Pew Research Center found 40% of highly religious Americans described themselves as “very happy,” relative to 29% of people who are less religious. Additionally, 65% of highly religious people had donated money, time, or goods to help the poor in the past week, relative to 41% who are less religious.

Lane pointed out that it’s unclear whether these effects are inspired by mystical experiences or an external factor such as being a part of a religious community that promotes charity. But, he said, spiritual practices that are done in solitude seem to have positive outcomes, which suggests that the mystical state, not just the culture surrounding religious institutions, promotes selflessness and happiness. (There have been hundreds of studies (paywall), albeit many poorly designed, that have found connections between long-term meditation and beneficial structural changes in the brain, too.)

At NYU and Johns Hopkins, the researchers are hoping the religious leaders will help compare and contrast naturally occurring and psilocybin-induced mystical experiences in ways current neuroscience cannot. Thus far, researchers have identified a feeling of “unity” or oneness of all things as the most prominent feature of both kinds of mystical experiences across varying groups of people. And Griffiths says there’s a connection between this sense of “unity” and an increase in selflessness: “If I’m not different than you, then I need to take care of you the way I would take care of me,” he says.

Anthony Bossis, the investigator leading the religious leaders trial at the NYU site, said it’s no coincidence that this sense of unity can also be found in the teachings of the world’s six principal religions (Christianity, Islam, Judaism, Daoism, Hinduism, and Buddhism). Bossis says the religious leaders in the trial are extraordinarily giving people, but that like most professionals in mental health or health care, they become emotionally taxed and experience what’s called “clergy burnout.” The researchers hypothesized that if the ministers reconnected to whatever god, or mystical experience, initially inspired them to embark on their life’s work, they would have a renewed energy to support their congregants. And thus far, their hypothesis seems correct. “They have increased passion for the scripture, for giving sermons, for helping people,” says Bossis. “If that’s sustained it will be remarkable.”

Cancer patients who had mystical experiences on the psychedelic DPT received the most relief from depression, anxiety, and a fear of death.

The religious leaders trial, as well as the rest of the psilocybin research, builds off medical studies done in the 1960s that were halted amid concerns about psychedelics’ rising recreational popularity. Bill Richards, an investigator on the religious leaders trial at the Johns Hopkins site, conducted some of the earliest and most influential psychedelic research at that time. In one study published in 1977, he found that cancer patients who had mystical experiences on the psychedelic DPT received the most relief from depression, anxiety, and a fear of death.

Bossis and Richards say their current priority is making psilocybin available for end-of-life distress. Much like Albert Hofmann, the inventor of LSD, once envisioned, they hope to see nationwide treatment centers where people with end-of-life distresses can take psychedelics in a safe, supportive setting. Stephen Ross, chief of addiction psychiatry at NYU, recently said at the Horizons Conference that they also hope to study psilocybin’s impact on eating disorders, criminal recidivism, and conflict resolution, among many other timely issues.

This is all a part of what’s now being called the “psychedelic renaissance” with MDMA (often confused with its recreational version ecstasy) on track to be administered by psychotherapists for post-traumatic stress disorder (PTSD) by 2021; the growing legalization of cannabis nationwide; and a positive response among the public to the psilocybin trials for cancer patients.

With all the progress, there’s a palpable optimism among psychedelic researchers that they may finally be moving past the stigma that has halted their research for a generation. Yet they remain careful about how they frame what they’re doing. Part of this includes explaining mystical encounters in a scientific context.

William James, aware of the bias against spirituality more than a century ago, took special care to do this too. That’s why, as a respected psychologist from Harvard University, he chose to spend the first chunk of his investigation into religious experiences simply justifying his project. He argued that the disputed purpose of mystical states bares no relevance on the reality that these experiences shift people’s outlook on life. That, in and of itself, makes them worthy of scientific inquiry.