This study looked at quantitative and qualitative data from 608 participants who reported extended difficulties following psychedelic experiences.

The most common forms of extended difficulty were feelings of anxiety and fear, existential struggle, social disconnection, depersonalization and derealization.

For approximately one-third of the participants, problems persisted for over a year, and for a sixth, they endured for more than three years.

It was found that a shorter duration of difficulties was predicted by knowledge of dose, drug type and lower levels of difficulty reported during the psychoactive experience, while a narrower range of difficulties was predicted by taking the drug in a guided setting.