A study of adults who used psychedelics found that about 33% experienced visual effects resembling hallucinogen persisting perception disorder (HPPD) 4 weeks afterward, but less than 1% found them distressing. Delusional thoughts reduced significantly, especially in those who had only used psychedelics a few times prior. Younger participants, women, and those with psychiatric conditions were more likely to report HPPD symptoms. Most participants were young adults with a mean age of 28.9 years.

Source: PNAS Nexus