BY SCOTT ALEXANDER: For More Info, Go Here…

Hallucinogen persisting perceptual disorder is a condition where people who take psychedelics continue hallucinating indefinitely. Estimates of prevalence range from about 4% of users (Baggott) to “nobody, the condition does not exist” (Krebs and Johansen). To explore this discrepancy, I asked about it on the 2019 SSC survey. The specific question was:

Hallucinogen Persisting Perceptual Disorder is a condition marked by visual or other perceptual disturbances typical of psychedelic use that continue for weeks and months after coming off the psychedelic, in some cases permanently. Have you ever had this condition?

2,234 readers admitted to having used psychedelics. Of those, 285 (= 12.8%) stated that they had some hallucinations that persisted afterwards. 219 (9.8%) said they’d had them for a while and then they had gone away. 66 (= 3%) stated that they still had the hallucinations (one limit of the study: I don’t know how long it has been since those people took the psychedelics).

But most of these people reported very mild experiences; on a scale from 1-10, the median severity was 2. The most commonly reported changes were more “visual snow” (ie “static” in the visual field), slight haloes around objects, and visual trails. Many people reported that if they stared at a textured area like a carpet long enough, illusory geometric patterns would start to form. Only a few people noticed anything weirder than this. Here are some sample responses:

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