On a recent Friday night, a dozen seekers in loosefitting attire, most in their 20s and 30s, climbed a flight of steps of a mixed-used community space in Bushwick, Brooklyn. After arranging yoga mats and blankets on the floor, they each paid $150, listened to a Colombian shaman and his assistant welcome them in Spanish and English, signed a disclaimer, and accepted large plastic takeout-style containers for vomiting.

Then, one at a time, each got up to receive a cup of thick brownish liquid with a muddy herbal taste. It was ayahuasca (eye-uh-WAH-skuh) tea, a hallucinogenic brew from the Amazon that they hoped would open them to personal insights through optic and auditory hallucinations.

Once they drank and had settled into their spots, they waited in the darkness with just one candle flickering. The shaman played traditional stringed and wind instruments while chanting ritualistic melodies, some sweet, some guttural.

A participant who asked that her name not be used because it might jeopardize her teaching positions at several graduate programs in Manhattan settled in for the all-night journey. She had abstained for several days from alcohol, red meat, spicy foods, aged cheese and television, as prescribed by email. She had not had sex and she was not on antidepressants.