Dr. Dan Engle, a psychiatrist in Boulder, Colo., warns that another risk for people in their 70s and 80s is the number of pharmaceutical drugs that are contraindicated for ayahuasca, including the most common form of anti-depressants, Selective Serontonin Reuptake Inhibitors (S.S.R.I.s). “But all of that said, ayahuasca is a visionary medicine and it can heal core psychological wounds,” Dr. Engle said. “At that stage in their life, in their 70s and 80s, ayahuasca can help people become present and have more acceptance.”

None of the medical caveats deterred James Kilkenny, 70. Mr. Kilkenny, a construction manager who lives in Manhattan’s West Village, began experimenting with ayahuasca over the last few years, after hearing about it from a friend who teaches yoga. He said that at this point, he’s done about 25 ayahuasca ceremonies.

He’s certainly not in it for pleasure-seeking. “Ayahuasca journeys for me are not fun,” he said. “They’re painful as hell. They can give you diarrhea and vomiting, sometimes one, sometimes the other, sometimes both at the same time.” Beyond the physical, there’s the unpredictable emotions: At times he has felt trapped, fearful and isolated. “And you can’t think your way out of it.”

Yet Mr. Kilkenny said he has gained extraordinary insight. During one ceremony in Peru, he said he was transported back to the earliest sense he had as a kid. “I knew that my childhood, while it wasn’t abusive, was very very cold. It had very little approval or affection in it. What I saw that night was: picture an upside-down pyramid. That point of the pyramid was the first thought. The first thought was loneliness and need for affection and approval. And the pyramid going up from that was my whole life. So my whole life was based on that one moment, seeking affection and approval.”

For Mr. Kilkenny, what the ayahuasca journeys have provided him with is profound “information.” Now, in the moments when he recognizes his own need for validation , he is less inclined to act on it. This has meant that certain relationships have become untenable, like a longstanding romantic involvement that had a lot to do with “neediness.” The relationship’s dissolution made him sad, but did not crush him.

“My life is a lot quieter and it’s a lot more peaceful,” he said. “Less seeking, less grasping, less needing. Less fear.”