Hallucinogen persisting perception disorder

Hallucinogen persisting perception disorder (HPPD) is a non-psychotic disorder in which a person experiences apparent lasting or persistent visual hallucinations or perceptual distortions after a previous use of drugs, including but not limited to psychedelics, dissociatives, entactogens, tetrahydrocannabinol (THC), and SSRIs. Despite being designated as a hallucinogen-specific disorder, the specific contributory role of psychedelic drugs is unknown. The hallucinations and perceptual changes consist of, but are not limited to, visual snow, trails and after images (palinopsia), light fractals on flat surfaces, intensified colors, altered motion perception, pareidolia, micropsia, and macropsia. People who have never previously taken drugs have also reported some symptoms associated with HPPD (such as floaters and visual snow). HPPD is a DSM-5 diagnosis with diagnostic code 292.89 (F16.983). For the diagnosis to be made, other psychological, psychiatric, or neurological conditions must be ruled out and it must cause distress in everyday life. In the ICD-10, the diagnosis code F16.7 corresponds most closely to the clinical picture. HPPD is rarely recognized amongst both hallucinogen users and psychiatrists, and is often misdiagnosed as a substance-induced psychosis. Newer research makes a distinction between HPPD I and HPPD II. The more drastic cases, as seen in HPPD II, are believed to be caused by the use of psychedelics as well as comorbid mental disorders. Some people who have this disorder report that they developed symptoms of HPPD after their first use of such drugs (most notably LSD). Because research regarding HPPD is currently lacking, there is little information on effective treatments, its aetiology and relationship to other disorders, and precise mechanism. In 1898, the English physician and intellectual Havelock Ellis reported a heightened sensitivity to what he described as "the more delicate phenomena of light and shade and color" for a prolonged period of time after he was exposed to the hallucinogenic drug mescaline.