Hallucinogen-persisting perceptual disorder (HPPD) has not been observed in thousands of participants in psychedelic studies.

“There is a phenomenon that appears real, that's called hallucinogen-persisting perceptual disorder. It's in the DSM. A certain number of people, a very small number of people percentage-wise who have used psychedelics, will have these persisting perceptual disorders, like they'll see halos around things. They'll see some trails, like the after image is following an object in motion. They'll see distortions in color. And it'll be like anything else that's a disorder in the DSM. It has to be clinically distressing, and it has to be persisting over some number of months.”