Abnormal visual experiences in individuals with histories of hallucinogen use: a Web-based questionnaire.

Despite longstanding reports of prolonged or reoccurring perceptual changes in a subset of hallucinogen users, very little is known about Hallucinogen Persisting Perception Disorder and related visual abnormalities in hallucinogen users. We used an online questionnaire to document the symptoms and relationship to drug use of unusual visual phenomena in hallucinogen users. 16,192 individuals viewed the information sheet and 2679 were included in the study. Of these, 224 reported having unrelated diagnoses associated with unusual visual experiences and were excluded from main analyses. Most (60.6%) of the remaining 2455 participants reported having experienced drug-free visual experiences that resembled hallucinogen effects. Probability of experiencing constant or near-constant symptoms was predicted by greater past exposure to specific hallucinogens, including lysergic acid diethylamide (LSD). Although symptoms were common, few (104, or 4.2% of the sample) found them distressing or impairing enough to consider seeking treatment. Visual changes in hallucinogen users may be more common than previously suspected and are worthy of further study.