Abnormal visual experiences in individuals with histories of hallucinogen use: A web-based questionnaire

Introduction

Hallucinogen use is common, especially among young adults, and a minority of users report prolonged or recurring perceptual changes. The DSM-IV-TR recognises a syndrome termed Hallucinogen Persisting Perception Disorder (HPPD), but the literature on its prevalence, phenomenology, and risk factors is limited and sometimes conflicting. Prior reports emphasise visual disturbances—geometric imagery, motion-perception abnormalities, halos, afterimages, and colour flashes—but many studies are case series or small samples, and some apparent cases may overlap with other conditions such as psychosis, migraine aura, seizures, or stroke. Whether persisting visual changes represent a rare complication of specific drugs (notably LSD) or a more widespread, drug-triggered vulnerability remains uncertain. Baggott and colleagues therefore conducted an exploratory web-based questionnaire study to document the frequency and characteristics of drug-free visual phenomena among people with histories of hallucinogen use, and to examine relationships between these experiences and past exposure to specific psychoactive substances. The investigators chose an online approach to access a large, difficult-to-reach population and to gather initial descriptive data that might guide more objective follow-up research.