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 using 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.

The mechanisms behind HPPD are still not well understood, and there is a lack of clear explanation regarding its causes. One of the current hypotheses suggests that anxiety may not only amplify existing visual disturbances but could also potentially trigger these visual phenomena. Many individuals with HPPD report that their visual distortions become more pronounced or even emerge during periods of heightened anxiety or stress. This indicates that anxiety may play a role in both the onset and intensification of these symptoms, making them more noticeable or cognitively magnifying the perception of such disturbances.