How it is measured

The Challenging Experience Questionnaire, built in 2016 from surveys of people who had taken psilocybin mushrooms, scores seven dimensions: grief, fear, death, insanity, isolation, physical distress and paranoia. Older altered-states questionnaires measure a related dimension called dread of ego dissolution.

How often it happens

Screening and preparation reduce the risk but do not remove it: in a dose-finding study at Johns Hopkins, 7 of 18 volunteers had extreme fear or anxiety when given one of the two highest doses. In a nationally representative US sample, 59 percent of 613 people who had used a classic psychedelic had never had a challenging experience, while 8.9 percent reported impaired functioning lasting more than a day. Serious harm is rarer: in a global survey of 9,233 people who had used magic mushrooms in the past year, 0.2 percent sought emergency treatment, about once in 1,800 uses, and all but one were back to normal within 24 hours. For a minority the difficulties last: among 608 people who reported extended difficulties, roughly one in three still had problems after a year.

What shapes the risk

In the same US sample, a negative mindset, no preparation, no psychological support, a dose that felt too large, a major life event beforehand and use of lithium or other mood stabilizers were linked to harder experiences. Among 1,993 people describing their worst psilocybin experience, only a quarter had a sitter present, yet 84 percent said they had benefited from it. Our checklist for choosing a psychedelic retreat includes questions about how a provider handles a difficult session.

Related terms

Set and Setting: expectations, mood and surroundings that color any session.

Psychedelic Integration: making sense of a hard session afterward.

Psychedelic Harm Reduction: practical ways to reduce harm when people use psychedelics on their own.