Hallucinogen persisting perceptual disorder: a scoping review covering frequency, risk factors, prevention and treatment

Introduction

Doyle and colleagues situate Hallucinogen Persisting Perception Disorder (HPPD) as a recognised but incompletely characterised consequence of prior hallucinogen intoxication, defined by recurrent perceptual disturbances (for example visual trails, halos, light intensification and visual snow) that persist after acute drug effects have ceased. The introduction distinguishes two subtypes: a common, transient ‘‘flashback’’ form (HPPD type I) reported in an estimated 5-50% of hallucinogen users, and a less common, more disabling and persistent form (HPPD type II) estimated at roughly 4.2% of users; diagnostic criteria used are those in DSM-5. The authors note renewed interest in serotonergic hallucinogens such as psilocybin for psychiatric treatment, and position HPPD as a safety concern warranting synthesis of the clinical literature. The stated aims of the scoping review were to summarise what is known about HPPD to inform clinicians: specifically, (1) which drugs are most frequently associated with HPPD onset, (2) what treatments have been used and their apparent success, (3) potential risk factors for HPPD, and (4) whether HPPD should be a concern in the context of potential therapeutic use of hallucinogens. The authors framed the work as a scoping review intended to map the heterogenous evidence rather than to produce pooled effect estimates.