Hallucinogen persisting perception disorder
Synonyms and keywords: HPPD

# Overview
Hallucinogen Persisting Perception Disorder or HPPD is a psychological disorder characterized by a continual presence of visual disturbances that are reminiscent of those generated by the ingestion of hallucinogenic substances.  Previous use of hallucinogens is a necessary, though not sufficient, cause for the disorder.  HPPD is distinct from flashbacks by reason of its relative permanence; whereas the latter is transient, the effects of HPPD occur for a prolonged or indefinite period.

# Symptoms
There are an array of perceptual changes that accompany HPPD.  Dr. Henry David Abraham
was the first to formally document the more quintessential features of the disorder.  These include the following visual abnormalities: halos 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, air assuming a grainy or textured quality (visual snow or static, by popular description), distortions in the dimensions of a perceived object, and a heightened awareness of floaters.  The visual alterations experienced by those with HPPD are not homogeneous; discrepancies may be evident in both the number of the preceding symptoms encountered and their respective intensity.
Although certain visual aberrations can occur periodically in healthy individuals  e.g. afterimages after staring at a light, noticing the floaters that lay atop the surface of the eye, or seeing specks of light in a darkened room  the difference is a matter of degree.  HPPD induces a hyper-sensitivity to ordinary visual phenomenon that would otherwise be negligible in their strength.  The disorder is thus capable of transforming mundane perceptual effects into a source of distress.  In this respect, HPPD can be considered a disinhibition of visual processing(Psychedelic Drugs, Abraham, et al, pg. 1548).  Yet it is important to emphasize that HPPD is chiefly responsible for creating new disturbances, rather than merely exacerbating those already in existence.  It also should be noted that the visuals do not constitute hallucinations in the clinical sense of the word; people with HPPD recognize the visuals to be illusory and thus demonstrate no inability to determine what is real (in contrast to Schizophrenia and other disorders that are known for serious changes in perception).
The visual problems of HPPD rarely exist in isolation; numerous mental ailments are often concomitant with the disorder.  Of these, the most prominent are anxiety, panic attacks, depersonalization disorder, and depression.  While it is difficult, if not impossible, to establish a clear relationship between the visual and mental symptoms, those with HPPD often testify that a connection indeed exists.  For example, anxiety can cause the visuals to become more prominent and vice-versa.  Anecdotal wisdom thus maintains that there is a synergistic link between the two.

# Differential Diagnosis
- Brain tumors
- Head trauma
- Infections
- Neurodegenerative disorders
- Schizophrenia
- Stroke

# Epidemiology and Demographics

## Prevalence
The prevalence of  is 4,200 per 100,000 (4.2%) of the overall population.

# Risk Factors
- Genetic predisposition

# Natural History, Complications and Prognosis

## Prognosis
Poor prognostic factors include:
- Alcohol use disorder
- Major depressive disorder
- Panic disorder

# Diagnostic Criteria

## DSM-V Diagnostic Criteria for Hallucinogen Persisting Perception Disorder

# Treatment
There is no universal course of HPPD development and recovery.  Regarding the former, HPPD typically emerges immediately after the conclusion of a hallucinogenic trip  as if the influence of the drug never completely dissipates.  However, a significant portion of the HPPD population suffer the visual change afterward, with the onset delay ranging from days to even months.  While it is probable that a victim will surmount many of the adverse psychological effects of HPPD (assuming they appeared at all), the visuals are known for their longevity.  As of yet, there is no cure available for HPPD.  The principal method of treatment is thus mitigation of both the visual and psychological aspects of the disorder.  Medications such as Valium and Xanax, and clonazepam/klonopin are prescribed with a fair amount of success.  Some medications have been contraindicated on the basis of their effects on HPPD or the concurrent mental issues.  The anti-psychotic drug risperidone is the most commonly cited member of this category, for it often renders the visuals uncomfortably powerful.  Convalescence can be facilitated by a psychological habituation to the visuals, which, in effect, reduces the victims inclination to react negatively to them.  The deleterious consequences of the visuals can therefore be abated even if the HPPD does not disappear.  Information pertaining to incidents of full recovery is tenuous.  The relatively small number of cases of HPPD which have been studied in any depth make it difficult to determine whether or not the visual symptoms of HPPD can disappear of their own accord, and if so, in what percentage of cases and under what conditions.  While there have been reports of HPPD victims being healed  that is, having normal perception totally return  it seems this is the exception rather than the rule.  Yet, as highlighted earlier, the quality of life will often return as a person adjusts.
Those with HPPD are advised to discontinue all illicit drug use and strictly limit their intake of alcohol and caffeine, both of which are known for bolstering visuals in the short-term.  And because HPPD frequently serves as a catalyst for various mental problems, it is imperative to refrain from abusing any type of drug, regardless of its legality.  Such behavior would be conducive to neither psychological nor physical health.  There are also less concrete factors that are generally detrimental to those with HPPD.  For example, sleep deprivation and stress are culpable of worsening both its visual and psychological complications.