Hallucinogen persisting perception disorder

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Hallucinogen persisting perception disorder
HPPD noise simulation, often referred to as visual snow

Hallucinogen persisting perception disorder (HPPD) is a chronic and non-psychotic disorder in which a person experiences apparent lasting or persistent visual hallucinations or perceptual distortions after a previous hallucinogenic drug experience, usually lacking the same feelings of intoxication or mental alteration experienced while on the drug. The hallucinations and perceptual changes themselves are usually not intense or impairing and consist of visual snow, trails and after images (palinopsia), light fractals on flat surfaces, intensified colors, or other psychedelic visuals. People who have never previously taken drugs have also reported some visual anomalies associated with HPPD (such as floaters and visual snow).[1][2]

HPPD is a DSM-5 diagnosis with diagnostic code 292.89 (F16.983).[3] For the diagnosis to be made, other psychological, psychiatric, or neurological conditions must be ruled out and it must cause distress in everyday life.[3] For example, poor concentration or difficult reading. In the ICD-10 , the diagnosis code F16.7 corresponds most closely to the clinical picture. HPPD is little known among both hallucinogen users and psychiatrists and is often misdiagnosed as a substance-induced psychosis.


In 1898, the English writer and intellectual Havelock Ellis reported a heightened sensitivity to "the more delicate phenomena of light and shade and color" for a prolonged period of time after consuming the psychedelic drug mescaline. This may have been one of the first recorded cases of what would later be called "HPPD".[4] However, mild residual effects or "afterglows" from these types of drugs are not necessarily unusual nor indicative of what can be classified as a disorder like HPPD since distress to the individual is usually a requirement for diagnosis.[3]


"Halos" are a often described symptom of HPPD

Typical symptoms of the disorder include: halos or auras surrounding objects, trails following objects in motion, difficulty distinguishing between colors, apparent shifts in the hue of a given item, the illusion of movement in a static setting, visual snow, distortions in the dimensions of a perceived object, intensified hypnagogic & hypnopompic hallucinations, and a heightened awareness of floaters. The visual alterations experienced by those with HPPD are not homogeneous and there appear to be individual differences in both the number and intensity of symptoms.[citation needed]

Visual aberrations can occur periodically in healthy individuals – e.g. afterimages after staring at a light, noticing floaters inside the eye, or seeing specks of light in a darkened room. However, in people with HPPD, symptoms are typically persistent enough that the individual cannot ignore them.[citation needed]

There is some uncertainty about to what degree visual snow constitutes a true HPPD symptom. There are many individuals who have never used a drug which could have caused the onset, but yet experience the same grainy vision reported by HPPD sufferers. There are a few potential reasons for this, the most obvious of which being the theory that the drug usage may exaggerate the intensity of visual snow.

Visual Snow with additional geometric hallucinations

Another theory is that instead, there may be no change in the severity or magnitude of the visual snow, but perhaps the drug usage opens sensory pathways that result in the individual becoming more aware of any visual disturbances that may have simply not been noticed before the incidence of substance use. As for root cause of visual snow, some theories suggest that it is the result of thermal noise in the visual cortex or in the 'Optic Pathway' as eye tests for individuals who experience visual snow often reveal that physically, the eye is perfectly normal, and in many cases the individual still maintains 20/20 vision.[5]

HPPD usually has a visual manifestation. Drugs affecting the auditory sense, like diisopropyltryptamine (DiPT), may produce auditory disturbances, though there are few known cases. Some hallucinogenic substances can produce temporary tinnitus-like symptoms as a side effect.

According to a 2016 review, there are two theorized subtypes of the condition.[3] Type 1 HPPD is where people experience random, brief flashbacks.[3] Type 2 HPPD entails experiencing persistent changes to vision, which may vary in intensity.[3] This model has faced scrutiny however due to "flashbacks" often being considered a separate affliction and not always a perceptual one.[6]


HPPD is not related to psychosis due to the fact those affected by the disorder can easily distinguish their visual disturbances from reality.[7] A vast list of psychoactive substances has been identified and linked with the development of this condition, including lysergamides like LSD and LSA, tryptamines like psilocybin and DMT, phenethylamines like 2C-B, MDMA, MDA and mescaline.[8][9] Dissociatives such as ketamine and dextromethorphan as well as cannabis and synthetic cannabinoids, salvia divinorum, datura and iboga are also known to trigger HPPD.[9] LSD seems to be the substance with the most reported cases of HPPD, 81 of 95 studies found LSD to be the substance that caused HPPD[10]

It is, therefore, clear that HPPD is not strictly associated with psychedelic consumption, but a number of hallucinogen-inducing substances may be correlated with its arising.[9] The dosage and how frequent one uses these substances doesn't seem to matter in the development of this condition since there's several reports in the litterature were people have gotten it after a single use.[9] Which strongly indicate that there is a genetic predisposition to this condition. It also seems that combining rectreational or medical drugs that act on the 5HT2-a receptors, like SSRI's, drastically increases the risk of developing it because of the drug-drug interaction.[11]

The exact pathophysiologic mechanism underlying HPPD is poorly understood. The primary neurobiological hypothesis is that persistent hallucinations are the result of chronic disinhibition of visual processors and subsequent dysfunction in the central nervous system following consumption of hallucinogens.[12][13] Chronic disinhibition may occur from destruction and/or dysfunction of cortical serotonergic inhibitory interneurons involving the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA).[14][15][16][17] This ultimately can cause disruption of the normal neurological mechanisms that are responsible for filtration of unnecessary stimuli in the brain. On a macroscopic level, the lateral geniculate nucleus (LGN) of the thalamus, which is important in visual processing, has also been implicated in the pathophysiology of HPPD.[18]


As of January 2022 there is no officially recognized cure or therapy for HPPD. The rate of spontaneous remission is very high with up to 50% of cases within a few months.[19]

Those affected with HPPD are heavily advised to discontinue all recreational drug uses also including legal stimulants like caffeine, taurine and nicotine, as many of them are thought to increase symptoms in the short term.[citation needed]

Antipsychotics such as aripiprazole or risperidone intended to treat mental disorders like schizophrenia should only be taken in careful consultation with a psychiatrist experienced in HPPD. The success rate of antipsychotics as a treatment method for HPPD is still debated. Two young men with HPPD and schizophrenia as a comorbidity experienced a remission of visual perceptual disturbance during a 6-month follow-up observation under treatment with risperidone.[10] There has been been a case study in 2013 where oral risperidone was also successful for treating HPPD.[20]In other cases risperidone has shown no effect on HPPD[10] or where it had a paradoxical effect and lead to permanent symptom exacerbation.[21]

Reports exist that various drugs provide partial or even complete remission.

  • Lamotrigine an anticonvulsant is the most popular medication for HPPD treatment. In the case of a 36-year-old man who suffered from HPPD for 18-years, the complex visual perception disorders largely resolved within 12 months after initiation of treatment with lamotrigine. In an another case a 33-year-old woman developed HPPD after abusing LSD for a year long at the age of 18. She reported afterimages, perception of movement in her peripheral visual fields, blurring of small patterns, halo effects, and macro- and micropsia. Previous treatment with antidepressants and risperidone failed to ameliorate these symptoms. Upon commencing drug therapy with lamotrigine, these complex visual disturbances receded almost completely. Lamotrigine is considered a possible treatment option for HPPD. Lamotrigine is generally well tolerated with a relative lack of adverse effects.[19]
  • Clonidine an antihypertensive that a pilot study of eight patients suggested could help significantly alleviate "LSD-related flashbacks."[22]
  • In a case study of two subjects suffering from synthetic cannabis-induced HPPD the symptoms significant improvement with Clonazepam treatment.[23] In a 2003 study 16 people with LSD-induced HPPD reported a significant relief and the presence of only mild symptomatology during clonazepam administration.[24]

Current research[edit]

The Australian Macquarie University is currently researching how HPPD affects the brain using Magnetic Resonance Imaging (fMRI) and Magnetoencephalography (MEG) studies to precisely measure the spatial and temporal activities of the visual pathways, which will be used to compare with control participants who are free from visual hallucinations.[25] Australians affected by HPPD and interested in participating can apply as probands.[26]


Estimates in the 1960s and 1970s were around 1 in 20 for intermittent HPPD among regular users of hallucinogens. In a 2010 study of psychedelic users, 23.9% reported constant HPPD-like effects, however only 4.2% considered seeking treatment due to the severity.[27] It is not clear how common chronic HPPD may be, but one estimate in the 1990s was that 1 in 50,000 regular users might have chronic hallucinations.[3]

Society and culture[edit]

In the second episode of the first season of the 2014 series True Detective ("Seeing Things"), primary character Rustin Cohle (Matthew McConaughey) is depicted as having symptoms similar to HPPD such as light tracers as a result of "neurological damage" from substance use.[28]

American journalist Andrew Callaghan, former host of the internet series All Gas No Brakes and current host of Channel 5, revealed during a 2021 interview with Vice News that he has a HPPD diagnosis as a result of excessive psilocybin use at a young age. Describing his symptoms, he noted that he experiences persistent visual snow and palinopsia.[29]


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