After Steve Witte was laid off from his job at Pfizer last year, he decided to pursue a radically different approach to medicine. Swapping his New York apartment for a thatch hut near Iquitos, Peru, Witte, 44, set aside his squash hobby to become an apprentice under the master shaman Alfredo Cairuna.

Like many of the traditional healers in this part of the Amazon, Cairuna—who is of the indigenous Shipibo people—serves as an intermediary between the physical and spiritual worlds, with the help of a hallucinogen known as ayahuasca, a plant-based concoction that has been used for centuries to treat a range of physical and spiritual maladies. Tourists, equally convinced that ayahuasca can alleviate everything from chronic pain to depression, have more recently turned its distribution into a thriving local industry. People “go back to work more calm and accepting—or they make huge decisions they weren’t able to before,” Witte says of those who come to visit Cairuna’s ayahuasca lodge. “People say it changes their lives.”

Slideshow: At an Amazonian healing ceremony, participants try to bridge the physical and spiritual worlds.

Served as a drink by Cairuna during an elaborate cere­mony that lasts for hours, ayahuasca is made mainly of the local ayahuasca and chacruna plants. It is thick and muddy and the color of clay. Drinking it usually occasions some intense vomiting, but that’s hardly the most extreme side effect. “It can be painful, and you can suffer, but it can also be intensely beautiful and enlightening beyond words. It can be a cleansing of your body in every way. I’ve seen people get really scared,” says Witte. “I just try to keep a calm mind, even if strange things happen.”

That advice is useful the night I first drink ayahuasca. It’s just after dusk, and the air is growing heavy with the calls of cicadas, frogs, and monkeys. I’m seated on a mat in a big room, joined by Cairuna, his wife, and two adult nieces, along with Witte and his translator. As the shaman-in-training, Witte begins the ceremony by reciting some prayers. He wears a white Shipibo gown painted with black tessellations, and finishes each blessing with a swig from a bottle of perfumed alcohol that he spits into the air in a spray that occasionally lands on our heads.

Before long, Cairuna calls each of us to kneel in front of him and offers a small bowl of ayahuasca. The concoction tastes something like decaying tree bark and dirt. “We’re going to be calm and present, and we’re going to listen to what the ayahuasca has to tell us. We’re all going to be fine,” Cairuna says reassuringly. Then he starts to sing icaros, ceremonial songs he’s told me to focus on as the ayahuasca takes hold—they’ll act as a reference point should the experience turn overwhelming.

I fidget uncertainly. After 20 minutes, I wonder if we got a bad batch. And then I realize that I’m seeing Cairuna’s songs: an indigo line quivers in front of me in sync with the pace and pitch of his singing. I watch, fascinated, and fixate on what I see and hear. Another 20 minutes later, I can’t open my mouth to speak, nor can I stand. I close my eyes to dull the panic and see fragments of memories as if on old film reels, which I watch for nearly an hour. Most of them involve events I haven’t thought of in years. When I open my eyes, I see a bear walk into the room on its hind legs and sit next to me. I know there is no bear, yet I perceive the heat radiating off its body. Focusing on Cairuna’s singing, I try to relax. The bear leaves and I feel somewhat victorious, though I don’t know why.

While ayahuasca can ravage a person physically—my skull and stomach feel like they’re filled with wet sand—it has the opposite effect on consciousness. After the ceremony, the mind feels light. My thoughts are oddly lucid and I find myself calmer than I’ve been in months. I can see why aya­huasca appears so effective in treating mood disorders like anxiety and depression, illnesses in which one’s flaws, trials, and disillusions often seem magnified and cripplingly heavy.

Lately, mainstream scientists have been inching toward a similar conclusion—by taking a closer look at the therapeutic potential of hallucinogenic drugs, they are discovering what shamans like Cairuna have known for generations. Though research of this kind was largely discontinued in the wake of Timothy Leary’s LSD experiments at Harvard in the 1960s, several major universities are now trying to unravel the mysteries of hallucinogens. Roland Griffiths, a professor in the departments of psychiatry and neuroscience at Johns Hopkins University—and one of the first to resume work on these drugs—published a study five years ago that demonstrated how effective they are at improving how a person feels. “That first study blew me away,” he says. “Nearly all the participants reported significant positive changes in attitude and behavior, and those changes were also observed by the participants’ friends, family, and colleagues. It was remarkable.”

Griffiths adds that while scientists have a long way to go toward understanding exactly how these compounds affect brain chemistry, they’ve come to agree that hallucinogenic experiences are about more than merely ingesting a drug. “There was one thing they got right in the 1960s: set and setting are extraordinarily important,” Griffiths says. “Look at cultures that use these compounds ritualistically—they do so in conditions that provide that crucial set and setting.”

In other words, Alfredo Cairuna, in his airy Amazonian lodge, has little reason to fear that Big Pharma might put him out of business with an aya­huasca pill anytime soon. Instead, he’s guessing that plenty more Americans will, like Steve Witte, seek him out, eager to learn the shaman’s craft.

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