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.”