A 29-year-old Canadian is being held in Peru for allegedly stabbing to death a British tourist after the two drank a hallucinogenic brew at a spiritual retreat in the Amazon.

Local authorities say the incident happened Wednesday night at a spiritual retreat near the town of Iquitos. The motive isn't clear, but local police chief Normando Marquez says a knife was pulled after a fight broke out.

The hallucinogenic drink ayahuasca has been venerated for centuries by indigenous tribes in the Amazon as a cure for all sorts of ailments. But it's also increasingly consumed by Westerners looking for mind-altering experiences.

The two men were guests at Phoenix Ayahuasca, which describes itself on its website as a "shamanic healing retreat." Phoenix didn't return emails and phone calls requesting comment.