On Perception and Consciousness in HPPD: A Systematic Review

Hallucinogen-persisting perception disorder (HPPD) involves perceptual symptoms and flashbacks after psychedelic use, but its phenomenology is poorly understood. A systematic review of 66 case reports and series covering 97 people identified 64 unique symptoms. Of these, 76% were characteristic of Alice in Wonderland syndrome, over 50% were non-visual, and 38% were not clearly linked to prior intoxication, contrasting with DSM-5 criteria. Fewer than half of patients had a protracted course over a year, and a third achieved remission. Co-occurring depression with or without anxiety was associated with longer symptom persistence and more negative treatment outcomes. HPPD involves changes in the content of consciousness and an attentional shift from external to internal phenomena, rather than the altered states seen in acute intoxication. The authors recommend expanding diagnostic criteria.

Study at a glance

Abstract

Hallucinogen-persisting perception disorder (HPPD) features as a diagnostic category in the DSM-5, ICD-11, and other major classifications, but our knowledge of the phenomenology of the perceptual symptoms involved and the changes in consciousness during the characteristic “flashbacks” is limited. We systematically evaluated original case reports and case series on HPPD to define its phenomenology, associated (psycho)pathology, and course. Our search of PubMed and Embase yielded 66 relevant publications that described 97 people who, together, experienced 64 unique symptoms of HPPD. Of these, 76% concerned symptoms characteristic of Alice in Wonderland syndrome, over 50% non-visual symptoms, and 38% perceptual symptoms not clearly linked to prior intoxication states. This is in contrast with the DSM-5 diagnostic criteria for HPPD. Even though less than half of the patients showed a protracted disease course of over a year, a third achieved remission. However, in patients with co-occurring depression (with or without anxiety) HPPD symptoms persisted longer and treatment outcomes were more often negative. Thus, unlike the acute stages of psychedelic drug intoxication, which may be accompanied by altered states of consciousness, HPPD is rather characterized by changes in the content of consciousness and an attentional shift from exogenous to endogenous phenomena. Since HPPD is a more encompassing nosological entity than suggested in the DSM-5, we recommend expanding its diagnostic criteria. In addition, we make recommendations for clinical practice and future research.