Background/rationale: In recent decades, we have witnessed the publication and promotion of promising research results regarding the therapeutic potential of psychedelic drugs, particularly in treating mental illness. Psychedelics are, however, much more used outside of research settings. Controversies have arisen regarding claims of uncritical positive regard surrounding psychedelics, with study designs/reporting styles biasing positive outcomes. 

Research-questions/hypothesis: Motivated by a desire to address this alleged bias and a dearth of research into lasting `negative` psychological responses, this exploratory study focused exclusively on such experiences, lasting for >72hrs after use of classic psychedelics/MDMA. We sought insight into why such responses may occur, aiming to inform on risk mitigation. 

Methods/analysis: A two-phased approach was used featuring 1) an onboarding questionnaire (completed by n=32) designed to collect quantitative descriptive data and screen for 2) a subsequent interview phase (n=15). The latter yielded richer qualitative data and constitutes the core of this study. 

Main findings: Thematic analysis was used to identify potential causal factors: unsafe/complex environments during/surrounding the experience, unpleasant acute experiences (classic psychedelics), prior psychological vulnerabilities, high/unknown drug quantities, young age. 

Conclusions: These exploratory findings corroborate mental health iatrogenesis via psychedelic-use, inferring a common, multifaceted, causal mechanism: combining of a pro-plasticity drug (often `over-dosed`) with adverse contextual conditions and/or psychological vulnerability.

We hope this small, proof-of-principle study will inspire others to advance on our methods to deepen our data pool of such important cases so that their occurrence can be better understood, and likelihood, minimised.