Allan Finney, the executive director of Ayahuasca Canada, a loosely organized group that provides safety and legal advice, said he first attended a ceremony in Peru when he was 59 years old.

Ayahuasca brew is made from boiling the vines of the Ayahuasca plant with the leaves of the chacruna plant. It can be brewed in anything from a cauldron to a slow cooker, although the ingredients ...